Simulation Modeling of the Effects of
Chronic Pollutant Stress on Plant
Processes and Plant Community
Dynamics
Modeling Pollutant Uptake and Effects
on the Soil-Plant-Litter System
'
R. J. Luxmoore2
Abstract: Five coupled models of water, carbon, and chemical dynamics in a soil-pl a n t - l i t t e r system are outlined.
Algorithms defining gaseous and particulate pollutant
uptake are described along with functions for chemical
effects on plant growth and l i t t e r decomposition. Some
simulation results of a deciduous forest i l l u s t r a t e the
importance of diurnal and annual cycles of environmental
conditions on pollutant movement in vegetation.
This
modeling approach has provided (1) insights into plant
physiological processes and t h e i r interactions, ( 2 ) identif i cati on of plant properties important i n pollutant uptake,
( 3 ) a1ternati ve hypotheses about pollutant effects, and
( 4 ) a unified basis f o r assessment of diurnal and long-term
pollutant impacts on plant communities.
'and a l l the king's horses and a l l the king's
men coul dn I t p u t Humpty together again.''
from Humpty Dumpty, Anon.
The discouraging words of the nursery rhyme
suggest that the synthesis of bits of an egg t o
a whole will not happen at l e a s t while horses
and men are in charge! Our task of trying to
couple together b i t s and pieces of mechanistic
information about the physiology of trees and
responses to soil and atmospheric environments
Simulation
i s no less awesome a challenge.
modeling is a remarkable tool f o r meeting t h i s
challenge, since through mathematics coupled
relationships may be quantified. In t h i s paper,
presented a t the Symposium on Effects of Air
Pollutants on Mediterranean and Temperate Forest
Ecosystems, June 22-27, 1980, Riverside,
California, U.S.A.
research
staff
member,
Environmental
Sciences
Divisi on,
Oak
Ri dge
National
Laboratory,
Oak
Ridge,
Tennessee
37830.
Operated by Uni on Carbi de Corporati on under
contract W-7405-eng-26 with the U .S. Department
of Energy. Publication No. 1553, Environmental
Sciences Division, ORNL.
paper, an outline i s presented of five models
that link together and provide a framework f o r
study of pollutant uptake and effects in the
whole plant environment complex. Some appl ications are shown and the use of models in
analysis of experiments i s explored.
Lastly,
some specul ati ons are presented about pol 1utant
impacts on whole plants and t h e i r diurnal
metabolism.
MODELING THE SOIL-PLANT-LITTER SYSTEM
The development of a unified approach t o the
modeling of t e r r e s t r i a1 processes has been
undertaken a t Oak Ridge. Five component models
of water, carbon, and chemical dynamics in a
soil-pi ant-1 i t t e r system were constructed and
linked together (Baes e t a1. 1976). The models
(table 1) are deterministic. The flow processes
are dependent on gradient terms calculated by
the models t o provide the flow driving forces
and empirical inputs are used to represent pathway
resistances
or
conductivities.
Flow
directions are not predetermined and the models
can be applied t o a range of different soilplant systems (e.g.,
coniferous, deciduous
f o r e s t ) by changing the empirical properties in
the input data. The reader i s referred t o the
documentation reports (table 1) f o r further
details.
g
Tab1 e 1--Some attributes of coup1ed models
describing carbon, water, and chemi cal dynamics
in the soil -pi ant-li t t e r system.
CoMFONErn
NAME
WATER
SOIL EHCHANBE
PROSPER ITEHMI
M O T mLUTl UPTAKE
SCEHM
CERES
TIME STEP
1 6 0 8 60 mi".
I S OR 00 mi".
wm
ATTRIBUTES
EVAPOTRANsflRATIOt
BY COMBINATION
EOUATION.
USES EMPIRICAL
DISTRIBUTION
COEFFICIENT
IKdl FOR SOIL
OF INTEREST.
W2 DIFFUSION
SOIL WATER FLOW
BY DARCV FLOW
EOUATION.
SUBSTRATE GHADt:
ENT EOUATION FOR
lRANSLOCAT10N
USES EMPIRICAL
RELATIONSHIP
BETWEENSURFACE
RESISTANCE AND
SURFACE WATER
POTENTIAL.
MUFF fI,11977;
IS OR
w m;".
IMPLEMENTS MODEL
3F DIFFUSION AND
MASS FLOW OF
SOLUTES TO ROOTS
BY BALDWIN. NYE
AND TINKER 119731.
USES INPUT VALUES
FOR POTENTIAL
GROWTH OF LEAF.
STEM. BOOT, FRUIT
EMPIRICAL LITTER
DECOMPOSITION
RELATIONSHIPS.
EMPIRICAL DATA
FOR SOIL HYDRAULIC PROPERTIES.
REFERENCE
h
EOUATION FOR
NET PHOTOSYN.
THESIS.
DIFMAS
BEGOVICH AND
JACKSON 118751
i s gas density (Ug/ml)
ra i s boundary layer diffusion
resistance (seclcm)
rs i s stomata1 resistance (seclcm)
SOLUTES
DRYADS
rm i s mesophyll resistance (sec/cm)
I 6 OR 80 mi".
SOLUTEUPTAKEBY
ROOTS AND LEAVES.
Ug i s uptake (iig/cm* leaf/sec)
DIFFUSIVE GAS UPTAKE
BY LEAVES.
GRADIENT EOUATION
FOR PHLOEM TRANSLOCATION
TRANSPIRATION FLUX
USED FOR XYLEM
TRANSPORT.
P U N T DEMAND FUNCTION DETERMINED BY
POTENTIAL SOLUTE
CONCENTRATION INPUT
VALUES.
The value of gi i s made to vary between zero
and ge depending on the level of pollutant in
leaf storage (Ei) as follows,
OIXON rn i l 119781
The coupling between models (fig. 1) shows
that every model has informati on transfer with
at least two other models, and these take place
on either an hourly time step or every 15 minutes during storm events. Hourly values of stomatal resistance and plant water potential from
PROSPER are used in CERES to determine photosynthesis and growth respectively.
Leaf and
root growth in t u r n influence transpiration and
thus soil water flow. During rainfall, i n f i l tration and the movement of water between soil
layers (calculated in PROSPER) i s used in the
soil chemistry model (SCEHM) to calculate chemical f l uxes.
Chemi cal concentrati on and root
water uptake information are used in DIFMAS t o
calculate chemical uptake into root by diffusion
and mass flow. Chemicals within the plant are
moved up in the transpiration stream and down in
the phloem pathway.
Em i s the maximum allowable level of pollutant in leaf storage, an input parameter.
Operationally this i s the pollutant level at
which the leaf tissue becomes necrotic.
ORNL-DWG 75-15812R2
JroweRI
This set of models can be run for simulation
periods of several years and annual budgets for
water, carbon and chemicals can be evaluated as
well as detailed results for hourly periods of
interest. The algorithms defining gaseous and
parti cul ate pollutant uptake and effects on
plant growth and l i t t e r decomposition are outlined in the next two sections along with
example simulation results.
AIR POLLUTANT UPTAKE
The uptake of a i r pollutants by vegetation
may occur directly through leaves (gaseous and
parti cul ate) or indirectly through roots after
the pollutants have been incorporated into soil.
Gaseous uptake i s represented by a diffusion
equation (same form as the photosynthesis
equati on ) Thus
.
where g i s the external pollutant concentration
(ml/ml)
gi i s the internal pollutant concentration
(ml/ml)
PROSPER soi 1-pi ant-atmosphere water f l ow model
carbon dynamics of vegetation and l i t t e r
soil chemistry model
DIFMAS diffusion andmass flow of chemicals t o
roots
DRYADS chemi cal dynami cs of vegetation and
1i t t e r
CERES
SCEHM
Figure 1--Coupling of five process models that
describe hourly carbon, water, and solute
dynamics of the soil-plant-litter system.
Sulfur dioxide uptake by an oak-hickory
f o r e s t in the v i c i n i t y of a lead mining and
smelter complex in southeastern Missouri was
simulated and r e s u l t s i l l u s t r a t e the behavior of
the model. Cumulative s u l f u r levels in leaves
( f i g . 2) show a rapid increase on t h e 25th of
August, a day in which the atmospheric SO2
level was increased 10 f o l d above ambient. The
translocation of s u l f u r from leaf t o stem
( f i g . 2 ) c l e a r l y shows a diurnal pattern and a t
elevated r a t e s on the 25th of August. Some of
the s u l f u r material t h a t was transported t o t h e
roots, leaked i n t o the t r a n s p i r a t i o n stream and
returned from t h e roots t o the stem, a l b e i t in
t r a c e amounts. The phloem and xylem transport
pathways can a l l ow considerable mobi 1i t y of solutes between plant t i s s u e s according t o the
simulation. The cumulative s u l f u r l e v e l s in t h e
l e a f , stem and root components ( f i g . 3 ) show
t h a t t h e majority of s u l f u r remained in t h e
leaves.
The value of 8 x 105 p g ~ / m 2 i s
equivalent t o a 1eaf concentration of 180 ppm.
distributed and has one of two f a t e s . I t may be
transported t o other plant parts or be incorporated in the leaf in an immobile form. The cut i c u l ar uptake process i s considered r e v e r s i b l e
in the model.
Thus during r a i n f a l l , wash-off
occurs and i f Se becomes l e s s than S i , then
leaching of pollutant out of leaves will occur.
ORNL- DWG 7 6 - 13390R
'06
6
ORNL- DWG 80-11126 €
10'
22
-
21
Figure
uptake
phloem
days in
23
25
27
DAYS IN AUG
29
31 2--Simul ated cumulative s u l f u r dioxide
by vegetation ( g/m2) and leaf t o stem
translocation r a t e ( pg/m^/h) f o r 11
August.
The uptake of p o l l u t a n t s from p a r t i c u l a t e s
deposited on leaves (Ui ) i s represented by a
gradient equation using empirical input values
f o r t h e c u t i c u l a r conductivity ( k l ) and thickThus,
ness ( W ) .
where S i s t h e external p o l l u t a n t on leaf
surface (g/m2 land)
S i i s t h e i n t e r n a l p o l l u t a n t within
f o l i a g e (g/m2 land)
The amount of dissolved pollutant on leaf
surfaces i s calculated as the l e s s e r of e i t h e r
t h e product of sol ubi 1i t y and the water volume
on leaves ( i n t e r c e p t i o n ) or the current amount
of p o l l u t a n t on leaves. The soluble p o l l u t a n t
within leaves ( S i ) i s assumed t o be uniformly
,
176
23
24
25
26
DAYS O F AUGUST
27
28
29
Figure 3--Simul ated s u l f u r elemental accumul at i o n in l e a f , stem, and root t i s s u e (pg/m2)
r e s u l t i n g from gaseous uptake.
S e n s i t i v i t y analysis of the leaf c u t i c l e cond u c t i v i t y ( f i g s . 4a, b) shows t h a t g r e a t e r
conductivity i s associated with greater chemical
(zinc in t h e example) uptake by leaves and a
s l i g h t l y reduced uptake of zinc from t h e s o i l
solution (Begovich and Luxmoore 1979).
This
l a t t e r and more s u b t l e e f f e c t i s induced by the
higher zinc level in t h e plant with higher conducti vi t y which feeds back a reduced chemical
demand in t h e root uptake algorithm. I t i s poss i b l e t h a t s u b t l e e f f e c t s may become s i g n i f i c a n t
when integrated over long time periods. Cuticul a r conductivity and t h e equivalent property a t
t h e root-soil i n t e r f a c e ( r o o t conductivity, k c )
were shown t o be very s e n s i t i v e parameters in
t h e model, and yet these are perhaps t h e l e a s t
well characterized experimentally. Results from
a s e n s i t i v i t y analysis of root conductivity on
lead uptake ( t a b l e 2) show large increases in
uptake by roots and lead c o n c e n t r a t i o ~ i n t r e e
t i s s u e s with increase in kr from 10"
cm/sec
t o 10-6 cmlsec.
The simulations a l s o show
t h a t pollutants accumulate p r e f e r e n t i a l l y in t h e
leaf and root, the s i t e s of pollutant entry. A
modification has subsequently been added t o t h e
model t o allow chelation of chemical within t h e
plant (Luxmoore and Begovich 1979) which has the
effect of i ncreasing the mobi 1i t y of pollutant
within the plant. Thus, the s i t e of pollutant
entry may not be the s i t e of accumulation.
The monthly pattern of lead uptake by roots
and foliage simulated for an oak forest near a
mine-smelter complex during the f i r s t year of
operation shows that uptake corresponds with the
growing season (table 3). The major proportion
(88%) of root uptake occurred during the day
chiefly due to two compl ementary transportation
processes; the mass flow of pollutant t o roots
and mass flow of pollutant from roots to shoots.
The l a t t e r was the controlling process in the
simulations. Overall, leaf uptake was more than
double that simulated for roots for the f i r s t
year of smelter operati on.
ORNL-OWG 80- 11127 ESD
Tabl e 3--Simul ated root and leaf
uptake, (mg pb/m2 landlmonth) of
lead by oak vegetation in the
vicinity of a mine-smel t e r complex.
2.0
-
1.8
-
I-
a!?
2
'
2
1.6
1.4
I
- --- -..-....-. /
-lo-'
10-9
!o-~~
10-13
Month
YT
-
1
0
Night
*.---
.-.--*'
Jan.
Feb.
March
April
-
May
June
July
Aug
Sept.
Oct.
Nov.
Dec.
-
,
.
0
5
10
15
20
DAYS IN JULY
25
30
Figure 4--a.
Influence of leaf cuticle permea b i l i t y on zinc uptake by leaves.
b.
Influence of leaf cuticle pennea b i l i t y on zinc uptake by roots.
Total
Tabl e 2--Sensi t i vity of annual root lead uptake and tissue concentration (prior t o leaf
f a l l ) in an oak forest to change in the root solute conductivity parameter ( k r ) .
I
Annual
root uptake
( pg/cm2/year)
I
September tissue concentration (ppm)
I
Stem
Leaf
Sapwood
Heartwood
I
Root
Sapwood
Heartwood
Fruit
Pollutant Impacts
Simple ramp functions are used to determine
pollutant effects on the growth and decomposition of leaf, stem, root and f r u i t components.
Separate ramp functions for either growth effects ( f i g . 5) or control of decomposition in
the l i t t e r (same form as for growth effects)
represent
ranges
of
chemi cal
def i ciency,
sufficiency, and toxicity as the chemical concentrati on increases.
Hypotheses concerning
benefici a1 ( f e r t i l i z e r ) and toxic pollutant
effects can thus be examined. The product of
the growth coefficient and tissue growth r a t e
(from CERES) provides a modified growth rate due
to pol 1u tant effects.
Figure 5--The re1 ati onship between the growth
coefficient (Gc) and the amount of element in
tissue (Ei) used t o represent deficiency
( E l < Ei < E?),
(Ei < E1)m sufficiency
effects of
the
and toxicity (Ei > E 2 )
elements on tissue growth rate.
parameters. The work presented i s best viewed
as "equipment" ; the subrouti nes being component
parts which collectively form a package of
hypotheses, theories, or knowledge in mathematical form. We need t o thoroughly t e s t models
through applications t o experimental studies as
much as possible to, hopefully, invalidate parts
of the model structure. The deviations of model
predictions from experimental findings provide
the key to new insights - in t h i s way models
f a c i l i t a t e the analysis and synthesis of complex
interactions. Putting models to work in t h i s
way requires data from well-documented experiments. For example, the uptake and physiological effects of gaseous pollutants have been
documented for several t r e e species (Jensen and
Kozlowski 1975, Thompson e t a1. 1967, Roberts
1974, Lawhon 1973, Houston and S t a i r s 1973), and
these experimental data can be used in leaf
physiological models (Kercher 1977) or in the
models outlined in the e a r l i e r sections. A considerable body of experimental data has been
developed for a i r pollutant effects on plants,
and i t i s timely to apply modeling techniques in
the research analysis of impacts. An alternat i ve approach i s one of conceptual extrapol a t i on
of the model behavior.
Some speculations are
presented in the next section.
Pollutants and the Diurnal Cycle
.
Next Step
The modeling of water, carbon, and chemicals
as coupled components in soi 1-pl ant-1 i t t e r
systems has stimulated the development of a conceptual framework for the diurnal cycle in
plants ( f i g . 6) that can be used t o invent
hypotheses of pollutant effects on whole
plants.
In the diurnal cycle, plants change
between two relative states:
( a ) lowest
sucrose, metabolite, and solute reserves at maximum hydration (dawn s t a t e ) ; and ( b ) highest
sucrose, metabol i t e , and solute reserves a t minimum hydration (dusk s t a t e ) . These states are
relative and apply to a given day. Photosynthesis recharges the plant with sucrose and
increases starch storage (or equivalent) during
the day. A t the same time, the plant i s also
recharging with nutrients and undergoing dehydration. The loss of water can reduce the r a t e
of cell expansion processes during the day with
greater growth being favored with rehydrati on.
Thus plants may need t o solve a timing imbalance
between carbon gain and uti 1ization by changes
in internal storage. The higher internal carbon
status of leaves during the afternoon may reduce
the significance of pollutant impacts on leaves
during t h i s part of the day. Photosynthesis may
be already slowed by product accumulation, or
alternatively detoxification mechanisms using
readily avai 1able carbon metabolites and/or
energy may more easily cope with pollutant ins u l t than during early morning when internal
carbon status i s lower.
The previous sections outline one particular
s e t of models and show some simulation results
including s e n s i t i v i t y analysis of selected
The diurnal pattern of behavior (fig. 6) also
suggests that root exudation of carbon compounds
could be f a c i l i t a t e d during the day. In the
A six-year simulation of heavy metal deposition, transport, and uptake in an oak-hickory
forest in southeastern Missouri showed that the
lead accumulation was greatest in the l i t t e r
(Luxmoore et a1. 1978). Root uptake of lead
i ncreased through the six-year period, whereas
leaf uptake was a constant for the repetitive
Due to the
annual deposition of 25 g Pb/m
buildup of lead in the plant tissues, the mort a l i t y of pl ant parts returned increasingly
greater amounts of lead to the l i t t e r system
The l i t t e r dry weight increased through the sixyear period by 949 g/m2.
This compares
reasonably with a difference of 1130 g/m2
between the l i t t e r mass at a control s i t e and a
s i t e exposed to equivalent heavy metal deposition (Watson e t a1. 1976). The simulation
results pose an alternative hypothesis to the
experimental inference of reduced rates of l i t t e r decomposition at the elevated levels of
heavy metal accumul a t i on (Jackson and Watson
1977), by showing that the same effect could be
obtained with increased mortality of plant parts.
.
same way, the carb6n supply t o mycorrhizae and
root nodules may be f a c i l i t a t e d . Disruption of
these processes through the impact of a i r poll u t a n t s may be of great importance t o understanding who1 e pl ant responses.
Pollutant
s t r e s s t h a t causes reduced ,photosynthesis and/or
greater r e s p i r a t i on in f o r e s t ecosystems may
decrease t h e carbon 1eakage t o mycorrhizal assoc i a t i o n s with roots, p o t e n t i a l l y decreasing the
extent and e f f i c i e n c y of t h e fungi in supplying
n u t r i e n t s back t o the t r e e .
T h u s , i t may be
f u r t h e r hypothesized t h a t phytotoxic a i r pollutants may cause f o r e s t ecosystems t o be l e s s
e f f i c i e n t in nutrient r e t e n t i on ( i .e., become
more leaky, see also OINeill et a1. 1977) and
conversely beneficial a i r p o l l u t a n t s may increase n u t r i e n t r e t e n t i on of f o r e s t ecosystems.
Elevated atmospheric CO2 l e v e l s may be an example of t h e l a t t e r .
I PHOTOSYNTHESISRECHARGESPL.hT
WITH SUCROSE
2 'LOWER WAlEm POTEhTIAL REDUCES CELL EXPANStON IMINIMUM G R M H RATE1
3. +ACTIVE SOLUTE UPTAKE FROM MASSFLOW POOL
5. ROOT EXUDATION PROMOTED. LESS ROOT SLOUGHING
& FASTERPHLOEMTRANSLOCATIONOFSUCROSEFROMLEAVESTOSTEMSANDROOTS
7 FASTER XYLEM TRANSPORT OF SOLUTES AND METABOLLTES FROM ROOTS TO STEMS AND LEAVES
SUCROSE
-
STARCH
CYTOPLASM
,
I
/
I'
-
SUCROSEP
SUELL
SOLUTES IN -^----P
CYTOPLASM
STARCH
SHRINK
SOLUTES IN
VACUOLE
SUMMARY
Modeling of pollutant i n t e r a c t i o n s with whole
pl ant processes has provi ded :
1
Insights about t h e processes and t h e i r
i n t e r r e l a t i o n s h i p s , e.g.,
( a ) Transpiration may f aci 11i t a t e pol l u t a n t uptake by transporting chemical
from roots t o stem thus maintaining a
favorable chemical gradient f o r continuing uptake.
( b ) Phloem and xylem may provide ready
transport pathways f o r pollutant movement
between plant p a r t s ( f i g . 3 ) .
I d e n t i f i c a t i o n of plant properties important in pollutant uptake. In particu1a r , 1eaf and root chemical conductivity
have great influence on pollutant uptake
( f i g . 5, t a b l e 2 ) .
Alternative hypotheses, e.g.,
increased
f o r e s t 1i t t e r in areas polluted with
heavy metals could be due t o increased
mortality of plant p a r t s in addition t o
reduced decomposition r a t e .
A basis f o r short-term ( d i u r n a l ) and
long-term
speculation
or
pollutant
impacts, e.g.,
( a ) Hourly changes in water, carbon, and
nutrient s t a t u s of pl ants may inf 1uence
physiological s e n s i t i v i t y t o pollutant
insult.
( b ) Pollutant disruption of carbon a l l o cation t o be1 owground processes may have
long-term n u t r i e n t cycling impacts.
LITERATURE CITED
\,
\
\,
NIGHT CONDITION
-
4. METABOLITE CYTOPLASM
S. ROOT SLOUGHING PROMOTED. LESS EXUDATION
6. SLOWER PHLOEM TRANSLOCATION REDUCED SUCROSEGRADIENT
7. ,SLOWER XYLEMSOLUTE AND METABOLITE FLUX - REDUCEDTRANSPIRATION
-
.OOMINANT EhERGV UTIL#.?ATsONFOR T M E PERIOD
N D L C E D B Y ROOT RESISTANCE TO TRANSPIRATION
Figure 6--Diurnal pattern of carbon, water, and
solute dynamics showing re1 a t i ve tendencies and
r e l a t i v e s t a t e s i n vegetation.
Perhaps, l i k e Humpty Dumpty, these attempts
a t deriving whole system understanding from the
pieces involved shows many cracks and flaws.
Nevertheless, we give i t a go! The key t e s t i s
our answer t o the question "Did we learn something t h a t we d i d n ' t know before?"
Baes, C. F., C. L. Begovich, W. M. Culkowski,
K. R. Dixon, D. E. Fields, J. T. Holdeman,
D. D. Huff, D. R. Jackson, N. M. Larson,
R. J. Luxmoore, J. K. Munro, M. R. Patterson,
R. J. Raridon, M. Reeves, D. C. S t e i n ,
J. L. Stolzy, and T. C. Tucker.
1976. The unified transport model. In
Ecology and analysis of t r a c e contaminants
progress report October 1974-December 1975.
R. I. Van Hook and W. D. Shults, eds.,
pp. 13-62. ORNL/NSF/EATC-22. Oak Ridge
National Laboratory, Oak Ridge, Tennessee
37830. 200 pp.
Baldwin, J. P., P. B. Nye, and P. B. Tinker.
1973. Uptake of solutes by multiple root
systems from s o i l , 111. A model f o r calcul a t i n g the solute uptake by a randomly
dispersed root system developing in a f i n i t e
volume of s o i l . Plant Soil 38:621-635.
Begovich, C. L., and D. R. Jackson.
1975. Documentati on and appl i c a t i on of SCEHM.
A model of s o i l chemical exchange of heavy
metals. ORNL/NSF/EATC-16. Oak Ridge
National Laboratory, Oak Ridge, Tennessee.
67 PP.
Begovich, C. L., and R. J. Luxmoore.
1979. Some s e n s i t i v i t y studies of chemical
transport simulated in models of the s o i l plant- 1i t t e r system. ORNL/TM-6791. Oak
Ridge National Laboratory, Oak Ridge,
Tennessee.
97 pp.
Lawhon, W. T.
1973. Radial growth and wood density of white
pi ne in re1 a t i on t o coal -deri ved envi ronmental pollutants. Ph.D. d i s s e r t a t i o n .
Graduate program in ecology, University of
Tennessee, Knoxvi 11e , Tennessee. 110 pp.
Dixon, K. R., R. J . Luxmoore, and C. L. Begovich.
1978. CERES - A model of f o r e s t stand biomass
dynamics f o r predicting t r a c e contaminant,
nutrient and water e f f e c t s . I. Model
description, 11. Model documentation. Ecol.
Model. 5: 17-38. 93-114.
Luxmoore, R. J., and C. L. Begovich.
1979. Simulated heavy metal fluxes in t r e e
microcosms and a deciduous f o r e s t . Internal.
Soc. Ecology. Model1 ing. J. 1:48-60.
Houston, D. B., and G. R. S t a i r s .
1973. Genetic control of s u l f u r dioxide and
ozone tolerance i n eastern white pine. For.
Sci 19: 267-271.
.
Huff, D. D., R. J. Luxmoore, J . B. Mankin, and
C. L. Begovich.
1977. TEHM. A t e r r e s t r i a1 ecosystem
hydrology model. ORNL/NSF/EATC-27. Oak
Ridge National Laboratory, Oak Ridge,
Tennessee. 153 pp.
Jackson, D. R., and A. P. Watson.
1977. Description of n u t r i e n t pools and
transport of heavy metals i n a forested
watershed near a lead smelter. J. Environ.
Qual 6: 331-338.
.
Jensen, K. F., and T. T. Kozl owski.
1975. Absorption and trans1 oeati on of s u l f u r
dioxide by seedlings of f o u r f o r e s t t r e e
species. J. Environ. Qual. 4:379-382.
Kercher, J. R.
1977. GROW1: A crop growth model f o r
assessing impacts of gaseous p o l l u t a n t s f rom
geothermal techno1 ogi es. UCRL-52247.
Lawrence Li vermore Laboratory, Cal i f orni a.
Luxmoore, R. J., C. L. Begovich, and K. R. Dixon.
1978. Modeling solute uptake and
incorporation i n t o vegetation and l i t t e r .
Ecol. Model. 5:137-171.
O'Neill, R. V., B. S. Ausmus, D. R. Jackson,
R. I. Van Hook, P. Van Voris, C. Washburne, and
A. P. Watson.
1977. Monitoring t e r r e s t r i a1 ecosystems by
analysis of nutrient export. Water, Air,
and Soil Pollut. 8:271-277.
Roberts, B. R.
1974. Fol i ar sorption of atmospheric s u l f u r
dioxide by woody plants. Environ. Pollut.
7:133-140.
Thompson, C. R., D. C. Taylor, M. D. Thomas, and
J. 0. Ivie.
1967. Effects of a i r pollutants on apparent
photosynthesis and water use by c i t r u s
t r e e s . Environ. Sci. Technol. 1:664-650.
Watson, A. P., R. I. Van Hook, D. R. Jackson,
and D. E. Reichle.
1976. Impact of a lead mining-smelting
complex on the f o r e s t f l o o r l i t t e r arthropod
fauna in t h e New Lead Belt region of
southeast Missouri. ORNL/NSF/EATC-30. Oak
Ridge National Laboratory, Oak Ridge,
Tennessee. 163 pp.
Data-Based Ecological Modeling of
Ozone Air Pollution Effects in a Southern
California Mixed Conifer Ecosystem1
Ronald N. K i c k e r t and Barbara
emm mill^
A b s t r a c t : The purpose of t h i s r e s e a r c h was t o determine t h e
e f f e c t s of ozone a i r p o l l u t i o n on a mixed c o n i f e r f o r e s t
ecosystem i n t h e San Bernardino National F o r e s t , C a l i f o r n i a .
We used an e c o l o g i c a l systems modeling approach i n conc e r t w i t h v a r i o u s b i o l o g i o a l s p e c i a l i s t s . This r. q u i r e d
conceptual model development, computer programming, and
t h e a n a l y s i s of o r i g i n a l p r o j e c t d a t a f o r model c a l i b r a t i o n .
fie found t h a t t h i s p r o c e s s l e d t o t h e i n v e s t i g a t o r s cond u c t i n g new r e s e a r c h o f an i n t e g r a t i v e n a t u r e . A s t r u c t u r e
f o r complex i n t e r a c t i o n s of f o r e s t e f f e c t s was produced.
I n s i g h t s on changes i n ecosystem dynamics and a worst-case
s c e n a r i o of f u t u r e f o r e s t changes were d e r i v e d . ,
We conclude t h a t sudden q u a l i t a t i v e changes i n c o n i f e r
f o r e s t composition can occur under t h e i n f l u e n c e of ozone
a i r p o l l u t i o n and t h e e x c l u s i o n of n a t u r a l f i r e e v e n t s .
I f i t were known t h a t a i r p o l l u t a n t s d i d n o t
a f f e c t people and t h e i r environments, s o c i e t y
would be l i k e l y t o have l i t t l e i n t e r e s t i n t h o s e
p o l l u t a n t s . The c e n t r a l i s s u e i s "What a r e t h e
effects?".
INSTITUTIONAL SETTING
I n t h e United S t a t e s , N a t i o n a l Ambient A i r
Q u a l i t y S t a n d a r d s f o r ozone have been l e g a l l y e s t a b l i s h e d w i t h a view f o r e f f e c t s on humans, t h e
primary s t a n d a r d , and s e p a r a t e l y f o r t h e e f f e c t s
p r e s e n t e d a t t h e Symposium on E f f e c t s o f A i r
P o l l u t a n t s on Mediterranean and Temperate F o r e s t
Ecosystems, June 22-27, 1980, R i v e r s i d e ,
California, U.S.A.
s e n i o r Systems Analyst and A s s i s t a n t
S p e c i a l i s t , r e s p e c t i v e l y , D i v i s i o n of
B i o l o g i c a l C o n t r o l , U n i v e r s i t y of C a l i f o r n i a ,
Albany, C a l i f .
on The b i o l o g i c a l , e c o l o g i c a l , and p h y s i c a l e n v i ronment, t h e secondary s t a n d a r d . Recently, t h e
s t a n d a r d s were r a i s e d from 0.08 t o 0.12 ppm f o r one
hour p e r y e a r (u.s. Environmental P r o t e c t i o n Agency
1979). I n view of t h e f a c t t h a t knowledge o f p o l l u t a n t e f f e c t s c o n t i n u e s t o develop, t h e c r i t e r i a
f o r j u s t i f y i n g t h e l e g a l s t a n d a r d i s expected t o
be re-evaluated e v e r y few y e a r s .
THE PROBLEM
I n e v a l u a t i n g c r i t e r i a f o r d e c i d i n g upon t h e
secondary s t a n d a r d f o r ozone, i t has been recognized throughout t h e 1970's t h a t b i o l o g i c a l and
e c o l o g i c a l e f f e c t s i n f o r m a t i o n was b i a s e d toward
t h e more r e d u c t i o n i s t i c l e v e l s , i . e . , biochemist r y , p l a n t s c i e n c e , p l a n t physiology, and, because
of l o g i s t i c a l problems w i t h l a r g e r s p a t i a l and
time s c a l e s , biased a g a i n s t , o r a t l e a s t f a i l i n g
t o c o n s i d e r , e f f e c t s on " n a t u r a l " e c o l o g i c a l s y s tems i n t h e landscape. B i o l o g i c a l e f f e c t s c r i t e r i a
have been based on d a t a f o r i n d i v i d u a l organisms,
but t h e d i r e c t and i n d i r e c t e f f e c t s on p l a n t and
animal communities have been mostly s p e c u l a t i v e
(u.s. Environmental P r o t e c t i o n Agency 1978).
H i s t o r y of The Study
O b j e c t i v e s of t h e E n t i r e P r o j e c t
I n 1973, t h e EPA e s t a b l i s h e d a s e v e r a l - y e a r
s t u d y of o x i d a n t e f f e c t s on t h e mixed c o n i f e r ecosystem i n t h e San Bernardino National F o r e s t . The
i n t e r p r e t a t i o n s d e r i v e d t o d a t e from t h i g p r o j e c t
have c o n s t i t u t e d t h e major s o u r c e of i n f o r m a t i o n
f o r t h e ecosystem c h a p t e r on a i r q u a l i t y c r i t e r i a
published by t h e EPA; however, t h e m a j o r i t y of t h e
d a t a i n t e g r a t i o n remains t o be completed. A s a f u r t h e r f o c u s o f t h e p r o j e c t , two y e a r s a f t e r i t was
i n i t i a t e d , t h e s e n i o r a u t h o r was brought i n t o
i n t r o d u c e computer s i m u l a t i o n a s a t o o l i n g u i d i n g
t h e c o l l e c t i o n , i n t e g r a t i o n and i n t e r p r e t a t i o n of
d a t a on f o r e s t r e s p o n s e s t o o x i d a n t s t r e s s . The
p o t e n t i a l use of t h i s s t u d y i n f u t u r e policy-making
r e q u i r e d an emphasis i n t h e modeling e f f o r t p a r t i c u l a r l y on long-term e f f e c t s , p r o j e c t e d e f f e c t s a t
d i f f e r e n t t h e o r e t i c a l l e v e l s of o x i d a n t f l u x , and
e f f e c t s on t h e b e h a v i o r of t h e n a t u r a l community
a s opposed t o i n d i v i d u a l organisms.
The modeling methods and philosophy used i n t h e
p r o j e c t have been d e s c r i b e d i n p r e v i o u s p u b l i c a t i o n s
( ~ i c k e r t1977a, 1977b, 1980).
O b j e c t i v e s o f t h e Modeling A c t i v i t y
There a r e two ways i n which t h e t o t a l s t u d y was
improved. Model development a i d e d t h e p r o j e c t i n v e s t i g a t o r s i n viewing t h e i r own work a s a p a r t o f
a n i n t e g r a t e d conceptual s t r u c t u r e . Also, w i t h t h e
d e s i g n of a g r a p h i c model of v a r i o u s subsystems,
discussions with investigators led t o t h e i d e n t i f i c a t i o n of q u e s t i o n s s u b s e q u e n t l y t u r n e d i n t o r e s e a r c h which o t h e r w i s e would n o t have been done.
A mixed t r e e s p e c i e s p o p u l a t i o n dynamics approach
l e d t o s e e d l i n g e s t a b l i s h m e n t experiments, s t u d y
p l o t s e e d l i n g r e g e n e r a t i o n s u r v e y s , and a compreh e n s i v e p e s t damage i n v e n t o r y , t o determine m o r t a l i t y p a t t e r n s . Data needed f o r c a l i b r a t i n g a s t a n d
moisture model l e d t o a seismograph survey f o r p l o t
s o i l d e p t h s which i n d i c a t e d s o i l w a t e r m o n i t o r i n g
p r o f i l e s were t o o s h a l l o w on s e v e r a l p l o t s . I n f o r mation r e q u i r e d f o r r o o t d i s e a s e and b a r k b e e t l e dynamics l e d t o more c a u t i o u s u s e of t h e smog i n j u r y
s c o r i n g procedure, a s well a s t o t h e dendrochronol o g i c a l a n a l y s i s o f t r e e r a d i a l growth.
S t r u c t u r a l Simplification--The g o a l of t h e ecosystem modeling e f f o r t i s twofold, and e q u a l l y d i v e r s e i n each d i r e c t i o n . Due t o t h e n a t u r e of t h e
SBNF p r o j e c t , i t was r e q u i r e d t h a t t h e modeler beg i n w i t h a l o c a l i z e d , real-world s i t u a t i o n and
make e x t e n s i v e u s e o f t h e l a r g e data-base i n cons t r u c t i n g t h e model. The real world s i t u a t i o n ,
from which t h e d a t a a r e d e r i v e d i s extremely v a r i a b l e , c o n s i s t i n g of an east-west t r e n d i n g mount a i n range which i n c r e a s e s i n e l e v a t i o n and changes
i n s p e c i e s composition a l o n g t h e same g r a d i e n t of
o x i d a n t f l u x , such t h a t e s s e n t i a l l y no c o n t r o l a r e a s
a r e p o s s i b l e . Given such a complex system, The
f i r s t g o a l of t h e modeling a c t i v i t y was t o break
down t h i s system s t r u c t u r a l l y i n t o i t s s i m p l i f i e d ,
b a s i c components and d r i v i n g f a c t o r s .
Experiments and Model Behavior-- The o t h e r h a l f of
t h i s g o a l was t o p r o v i d e answers t o t h e q u e s t i o n :
how might one u s e a s i m u l a t i o n model f o r computer
experiments t o a s s e s s t h e t o t a l i t y of t h e s e e f f e c t s ,
a c t i n g a l o n e o r s y n e r g i s t i c a l l y , on ecosystem s t r u c t u r e and f u n c t i o n ? A l i s t of e f f e c t s does n o t h e l p
p o l i c y makers v e r y much when t h e y a r e i n t h e p o s i t i o n of making d e c i s i o n s i n t h e f a c e of u n c e r t a i n t y - even l e s s does i t inform b i o l o g i c a l l y knowl e d g e a b l e people who r i g h t f u l l y s u s p e c t t h a t i n t e r a c t i o n s o c c u r between i t e m s on t h e l i s t t h a t w i l l
a f f e c t f u t u r e outcomes a s much o r more t h a n a summary of s i m p l e e f f e c t s could e v e r e x p r e s s . Thus,
t h e modeling e f f o r t h a s been developed t o a d d r e s s
the following questions:
I
f u l l long-term ecosystem e f f e c t s ? Is t h e r e
p o t e n t i a l i n t h i s system f o r sudden jumps and
i r r e v e r s i b l e trends?
The EPA/SBNF P r o j e c t h a s attempted t o e s t a b l i s h e f f e c t s o f ozone a i r p o l l u t i o n on t r e e
stem growth, f o l i a r i n j u r y , t r e e m o r t a l i t y ,
r e g e n e r a t i o n , cone p r o d u c t i o n , n u t r i e n t c y c l i n g , and i n s e c t and d i s e a s e occurrence.
What i s t h e consequence of t h e s e e f f e c t s when
combined t o g e t h e r i n a s i m u l a t e d ecosystem?
What time s c a l e i s n e c e s s a r y t o u s e t o s e e t h e
RESULTS
Because t h e modeling a c t i v i t y i s s t i l l b e i n g
conducted, t h e r e s u l t s p r e s e n t e d h e r e a r e n o t based
on experiments performed on t h e computer u s i n g t h e
models. R a t h e r , t h e y a r e based on i n s i g h t s gained
d u r i n g t h e model development p r o c e s s , from concept u a l i z a t i o n , t o mathematical f o r m u l a t i o n , t o comput e r coding, and a n a l y s i s of o r i g i n a l d a t a toward t h e
g o a l of c a l i b r a t i n g t h e models f o r t r e e s p e c i e s and
s i t e s w i t h i n t h e SBNF and t h e n a p p l y i n g t h o s e mode l s i n experiments of a i r p o l l u t i o n e f f e c t s .
How t h e Systems Modeling P r o c e s s Aided t h e P r o j e c t
A S t r u c t u r e f o r Complex I n t e r a c t i o n s
The e f f e c t s o f a i r p o l l u t i o n i n t h e f o r e s t ecosystem a r e n o t o n l y t h e d i r e c t v i s i b l e e f f e c t s
t h a t a c a s u a l o b s e r v e r might n o t i c e by d i s c o l o r e d
f o l i a g e on t h e t r e e s , b u t a l s o l e s s a p p a r e n t , b u t
nonetheless r e a l , i n d i r e c t e f f e c t s t h a t a r e s u b t l y
t r a n s f e r r e d through t h e system. Such i n d i r e c t c h a i n
r e a c t i o n s can o c c u r a t t h e l e v e l of i n d i v i d u a l
t r e e s , a t t h e p o p u l a t i o n l e v e l of t r e e s of a c e r t a i n s p e c i e s , and because of changes i n t h e m i x t u r e s
o f t h e l a t t e r over t h e long-term, changes which
occur a t t h e whole community l e v e l . A s a map of how
such changes can be t r a n s f e r r e d throughout t h e s y s tem, f i g u r e 1 d i s p l a y s some s i g n i f i c a n t p o r t i o n s
of a f o r e s t ecosystem which must be c o n s i d e r e d . The
r e f e r e n c e numbers a s s o c i a t e d w i t h each component i n
t h i s diagram p e r t a i n t o v a r i o u s k i n d s of environmental c o n d i t i o n s and b i o l o g i c a l organisms import a n t t o understanding changes o c c u r r i n g i n a f o r e s t
ecosystem. These numbers a l s o r e f e r e n c e p a r t i c u l a r
OIHER L E M A L
DEAD r R E E S
Figure 1--Components of t h e f o r e s t ecosystem d i r e c t l y and i n d i r e c t l y
a f f e c t e d by photochemical a i r p o l l u t i o n .
r e s e a r c h t o p i c s which have been s t u d i e d between
1973 through 1980 i n t h e San Bernardino National
Forest.
The purpose of t h i s overview i s t o p r e s e n t a n
i n t e g r a t e d , s i m p l i f i e d frame of r e f e r e n c e w i t h i n
which t h e d i s c o v e r i e s , r e s u l t s , and c o n c l u s i o n s from
t h e p r o j e c t may be viewed a s a whole.
While a f o r e s t i s more t h a n simply a group of
t r e e s , t h e l a t t e r i s by d e f i n i t i o n t h e dominant
l i f e form of such a system. Reference w i l l be made
t o t h e numbers i n v a r i o u s p a r t s of f i g u r e 1 . To
view t h e e f f e c t of a i r p o l l u t i o n ( 1 ) on a community
of t r e e s , i t i s n e c e s s a r y t o c o n s i d e r s e v e r a l r e l a t i v e l y s t a t i c s i t e and s o i l p r o p e r t i e s ( 7 ) , a s w e l l
a s v e r y dynamic m e t e o r o l o g i c a l c o n d i t i o n s such a s
a i r temperature and p r e c i p i t a t i o n ( 3 ) . s i n c e a l l of
t h e s e may c o n t r i b u t e t o a s y n e r g i s t i c e f f e c t of a
long-term, c h r o n i c a i r p o l l u t i o n exposure i n terms
of t r e e response. Some of t h e p r e c i p i t a t i o n ( 3 ) ,
depending on s i t e and s o i l c h a r a c t e r i s t i c s ( 7 ) ,
e n t e r s t h e s o i l a s a v a i l a b l e s o i l water ( 2 ) f o r
t r e e growth ( 3 , 9 ) . F o r l a c k of b e t t e r d a t a , we env i s i o n a i r temperature ( 3 ) a s a rough index o f h e a t
a v a i l a b l e f o r e n a b l i n g a v a i l a b l e s o i l water t o be
d e p l e t e d through w a t e r l o s t from t r e e l e a v e s t o t h e
atmosphere through t r a n s p i r a t i o n .
Over time, and depending on s e n s i t i v i t y between
and w i t h i n v a r i o u s t r e e s p e c i e s , some of t h e g r e e n
f o l i a g e ( 4 , 5 ) on t r e e s becomes i n j u r e d , d i s c o l o r e d
f o l i a g e ( 4 , 5 ) , and some of t h a t i s dropped from t h e
t r e e s . T h i s , added t o normal amounts o f n e e d l e shed
a f f e c t e d by t h e a v a i l a b i l i t y of s o i l m o i s t u r e ( 2 ) ,
becomes a p a r t of ground l i t t e r ( 6 ) .
The r e l a t i v e amount o f f o l i a g e t h a t changes
from green t o i n j u r e d i s thought t o have a b e a r i n g
on t h e r a t e of stem wood growth ( 8 , g ) o f t r e e s .
These t h r e e responses a r e thought t o be a s s o c i a t e d
with t h e r a t e of production of cones and t h e r e f o r e
seeds (13) f o r r e g e n e r a t i o n of new t r e e s . A s p o l l u t a n t s l e a d t o a g r e a t e r degree o f f o l i a g e i n j u r y
f o r some t r e e s p e c i e s , and stem growth i s reduced,
otherwise mature i n d i v i d u a l s o f t h e s e s p e c i e s produce l e s s and l e s s cones, i f any.
It h a s been mentioned how a i r p o l l u t i o n can i n c r e a s e t h e ground l i t t e r depths ( 6 ) . This i s s i g n i f i c a n t because s e e d s (1 3) of some t r e e s p e c i e s
have a b i o l o g i c a l behavior which i s adapted t o l i t t l e o r no ground l i t t e r f o r s p r o u t i n g and s u r v i v i n g 3s s e e d l i n g s (14,15) d u r i n g d r y summers ( t h e
e f f e c t o f a v a i l a b l e s o i l water ( 2 ) once a g a i n ) .
Many cones, s e e d s , and small s e e d l i n a s a r e l o s t t o
w i l d l i f e of v a r i o u s forms under n a t u r a l c o n d i t i o n s .
Any f u r t h e r r e d u c t i o n i n t h i s r e p r o d u c t i o n c h a i n
because of a i r p o l l u t i o n e f f e c t s can make continued
replacement o f some t r e e s p e c i e s a v e r y p r e c a r i o u s
circumstance.
Those s e e d l i n g s t h a t do s u r v i v e t h e f i r s t few
y e a r s e v e n t u a l l y grow t o a l a r g e r s i z e o f t e n c a l l e d
s a p l i n g s (1 6) i n t h e p o p u l a t i o n s t r u c t u r e . The ext e n t t o which t h e e f f e c t o f a i r p o l l u t i o n r e t a r d s
stem growth (8.9) simply t e n d s t o keep t r e e s i n t h i s
s i z e range f o r a l o n g e r t i m e , s u b j e c t t o t h e many
causes o f d e a t h which can occur. E v e n t u a l l y , some
s a p l i n g s grow i n t o l a r g e r s i z e s which a r e mature
(16) and p o t e n t i a l l y capable of producing cones, a s
w e l l a s b e i n v a l u e d f o r e s t h e t i c purposes and a s
p o t e n t i a l l y merchantable timber.
Those mature t r e e s t h a t develop a s i g n i f i c a n t
degree of v i s i b l e f o l i a g e i n j u r y ( 4 , 5 ) a r e somet i m e s c u t down whether l e g a l l y o r by poaching. T h i s
produces stumps. I t h a s been discovered t h a t t h e
d e g r e e of f o l i a g e i n j u r y ( 4 , 5 ) , namely t h e younger
t h e age of t h e o l d e s t n e e d l e s , i s s i g n i f i c a n t l y
c o r r e l a t e d with t h e i n c i d e n c e of i n f e c t i o n and c o l o n i z a t i o n of such stumps by t h e r o o t r o t d i s e a s e
( 1 0 ) Fomes annosus, i f t h e f r e s h stumps a r e n o t
t r e a t e d e n t h e l i v e t r e e i s f i r s t c u t . One would
h a r d l y be concerned about t h i s i f i t were n o t f o r
t h e o b s e r v a t i o n t h a t such d i s e a s e s can spread from
dead stump r o o t systems i n t o a d j a c e n t l i v e t r e e r o o t
systems, from s e e d l i n g s , up t o l a r g e , mature, p o l l u t i o n - r e s i s t a n t t r e e s , depending on t h e s p a t i a l
d e n s i t y of t h e s t a n d . When t h i s does happen w i t h
t h e l a t t e r , and t h o s e t r e e s a l r e a d y have a c o n s i d e r a b l e d e g r e e of i n j u r e d f o l i a g e ( 4 , 5 ) , t h e n , especi a l l y on ponderosa p i n e , bark b e e t l e s (1 1 ) appear
b e t t e r a b l e t o s u c c e s s f u l l y a t t a c k and k i l l such
t r e e s . M o r t a l i t y s u r v e y s show numerous o t h e r p a t t e r n s o f d i s e a s e and i n s e c t combinations (1 2) a l s o
a c t t o k i l l t r e e s . Reduced growth cannot be s u s t a i n e d i n d e f i n i t e l y , and t h e l e n g t h of t i m e of r e duced growth p r i o r t o d e a t h a p p e a r s t o be agedependent.
Over t i m e , t h e complexion of t h e f o r e s t ecosystem w i l l change a c c o r d i n g t o which t r e e s p e c i e s a r e
b e s t a b l e t o r e s i s t t h e agents t h a t cause death
( 1 6 ) , whether n a t u r a l o r human-caused, and a r e a l s o
c a p a b l e of p r o v i d i n g new young s e e d l i n g s (1 4,15)
a b l e t o s u r v i v e t o m a t u r i t y . I n many c a s e s , t h e
evidence seems t o i n d i c a t e t h a t t h e b a l a n c e between
various t r e e species i s s h i f t i n g dramatically i n
t h e San Bernardino N a t i o n a l F o r e s t .
Given t h r e e d i r e c t e f f e c t s of a i r p o l l u t a n t s on
f o r e s t growth, namely f o l i a r i n j u r y and a c c e l e r a t e d
n e e d l e c a s t , woody growth r e d u c t i o n , and i n d i r e c t l y
i n c r e a s e d m o r t a l i t y , t h e s e e f f e c t s might be t i e d
t o g e t h e r i n t h e f o l l o w i n g s c e n a r i o s of ecosystemlevel effects.
Ecosystem Dynamics Under a S i n g l e S t r e s s
F o l i a r I n j u r y Consequences-- F o l i a r i n j u r y and premature shedding of p a s t y e a r ' s n e e d l e s w i l l slow
down t h e n a t u r a l development of canopy c l o s u r e i n a
s t a n d . It h a s been shown and r e p e a t e d l y confirmed
t h a t a s a s t a n d grows, l e a f a r e a expands u n t i l i t
r e a c h e s a p l a t e a u , a t which i t remains f o r t h e r e mainder o f t h e l i f e of t h e s t a n d ( ~ r i e rand o t h e r s
1978) ( f i g . 2 ) . Stand growth, developmental p a t t e r n s
and time t o m a t u r i t y a r e e n t i r e l y dependent
upon t h e r a t e o f canopy c l o s u r e . Net p r o d u c t i o n by
coniferous f o r e s t s is related t o l e a f area
( W h i t t a k e r and N i e r i n g l 9 7 5 ) , and a l l o t h e r t h i n g s
being equal, t h e g r e a t e r t h i s l e a f area, the g r e a t e r
i s t h e p r o d u c t i v i t y . Once maximal l e a f a r e a (canopy c l o s u r e ) i s o b t a i n e d , o t h e r ecosystem f u n c t i o n s
b e g i n t o make major q u a l i t a t i v e changes, a s d i s c u s s ed below. I f time t o canopy c l o s u r e i s i n c r e a s e d ,
n o t o n l y a r e p r o d u c t i v i t y r a t e s reduced, b u t a l s o
q u a l i t a t i v e e c o l o g i c a l changes may occur.
S i n c e f o r e s t f o l i a g e always t e n d s toward formi n g a c o n t i n u o u s , complete s u r f a c e a r e a , t h e degree
of completion r e p r e s e n t s t h e d e g r e e of occupancy of
t h e s i t e . A vigorous, healthy stand of t r e e s w i l l
STAND AGE- YEARS
Figure 2--Natural
f o r e s t s t a n d canopy c l o s u r e .
achieve occupancy o f a n open s i t e a t about 1 2 y e a r s
of age, e s t a b l i s h i n g dominance o v e r competing veget a t i o n , and w i l l m a i n t a i n occupancy u n t i l a t l e a s t
middle age ( s m i t h 1962). A given g e n e r a t i o n o f
t r e e s u l t i m a t e l y l o s e s command of t h e s i t e , g i v i n g
way t o younger members a n d / o r o t h e r s p e c i e s . A'fore s t canopy e x p e r i e n c i n g p o l l u t i o n - c a u s e d i n j u r y
might n o t be a b l e t o f u l l y e s t a b l i s h occupancy of
t h e s i t e . The amount o f accompanying v e g e t a t i o n ,
e s p e c i a l l y of an u n d e r s t o r y n a t u r e , might i n d i c a t e
t h e d e g r e e t o wh'ich t h e main s t a n d f a l l s s h o r t of
f u l l occupancy.
Growth Reduction Consequences-- Leaf a r e a i s d i r e c t l y r e l a t e d t o woody p r o d u c t i o n i n a f o r e s t s t a n d ,
a s mentioned. Impediments t o l e a f a r e a expansion
and canopy c l o s u r e might a f f e c t t h e o v e r a l l p a t t e r n
of woody growth i n a s t a n d . S t u d i e s have shown t h a t
second-year n e e d l e s a r e more i m p o r t a n t i n p r o v i d i n g
photosynthate f o r stem growth, while c u r r e n t y e a r
n e e d l e s c o n t r i b u t e p r i m a r i l y t o s h o o t and n e e d l e
e l o n g a t i o n (walker and o t h e r s 1972); t h e second
y e a r n e e d l e s a r e t h e most impacted by a i r p o l l u t i o n . Trees might c o n t i n u e t o p u t on h e i g h t growth
a t t h e expense of d i a m e t e r growth f o r a l o n g e r peri o d of time t h a n with a normally c l o s i n g canopy,
both because of a l a c k of p h o t o s y n t h a t e f o r stem
growth and because t h e open canopy f o s t e r s r a p i d
h e i g h t growth r a t e s . However, because growth and
p r o d u c t i v i t y i s s u p p r e s s e d , both h e i g h t and diamet e r growth r a t e s i n g e n e r a l would be much s l o w e r
t h a n normal.
I t i s a t e n e t o f s i l v i c u l t u r e t h a t changes i n
s t a n d d e n s i t y do n o t s i g n i f i c a n t l y a l t e r t h e t o t a l
amount of d r y m a t t e r o r stem wood produced by a
s t a n d . Thus, precommercial t h i n n i n g s do n o t markedl y change production r a t e s b u t r a t h e r add t h e same
amount of wood t o a l e s s e r number o f t r e e s ( s m i t h
1962). Mathematically, mean p l a n t s i z e m u l t i p l i e d
by d e n s i t y t e n d s toward a c o n s t a n t . T h i s r e l a t i o n s h i p h a s been confirmed t o hold t r u e f o r many veaet a t i o n t y p e s , i n c l u d i n g f o r e s t s t a n d s (cooper
1961). I n a p o l l u t i o n s t r e s s e d f o r e s t , however, one
might expect t h e r e l a t i o n s h i p e i t h e r t o be weak, o r
t o break down a l t o g e t h e r ( f i g . 3 ) . A t low d e n s i -
-unstressed forest
I
STAND DENSITY
-
TREES/ ACRE
Figure 3--Relation between stand d e n s i t y and average
t r e e s i z e with and without a i r p o l l u t i o n .
t i e s , mean p l a n t s i z e i s not remarkably l a r g e a s
t h e t r e e s a r e n o t i n good v i g o r ; a t high d e n s i t i e s ,
p l a n t s i z e i s suppressed even more than would be
expected due t o d e n s i t y e f f e c t s alone. I n e s p e c i a l l y damaged and open s t a n d s , t h e r e l a t i o n s h i p might
be expected t o break down. The functioning of t h e
r e l a t i o n s h i p i s dependent upon t r e e s e x e r t i n g an
i n f l u e n c e over each o t h e r . I f a l l t r e e s a r e genera l l y weakened i n competitive a b i l i t y , t h e i r growth
w i l l depend more on l i m i t a t i o n s imposed by t h e phys i c a l environment and l e s s on i n t e r - t r e e i n f l u e n c e s .
An open stand with highly v a r i a b l e t r e e s i z e s might
be t h e r e s u l t .
Tree M o r t a l i t y Consequences-- T y p i c a l l y , a stand of
t r e e s achieves a d e n s i t y i n balance with t h e physic a l environment by means of d e a t h of l e s s competit i v e t r e e s i n t h e s t a n d . Thus, t h e r e i s g e n e r a l l y
a continuous d e c l i n e i n stand d e n s i t y with i n c r e a s i n g stand development. I n a p o l l u t i o n - s t r e s s e d f o r e s t , one f i n d s t h e phenomenon of s e l e c t i v e m o r t a l i t y . However, t h e magnitude of t h e m o r t a l i t y can be
g r e a t e r and t h e cause i s o t h e r than simple competit i v e s t r e s s . A s young t r e e s prematurely age, t a p e r
o f f i n growth, and d i e , more openings a r e c r e a t e d
i n t h e canopy. While i n a h e a l t h y f o r e s t t h i s provides room f o r t h e dominant t r e e s t o expand, i n
p o l l u t i o n - s t r e s s e d f o r e s t s t h e open canopy i s opened f u r t h e r . Even i f t h e p o l l u t i o n should be removed
from t h e system, a lower stand d e n s i t y because of
increased m o r t a l i t y r a t e s r e q u i r e s a g r e a t e r time
t o develop a f u l l canopy than would a stand with a
more normal s t o c k i n g r a t e .
p r o t e c t n a t u r a l landscape ecosystems i f those changes a r e a s s o c i a t e d with human i n f l u e n c e s . E f f e c t s
of a i r p o l l u t i o n on f o r e s t s can have t h i s trend
s t a t e nature.
A Worst-case Scenario of Future Forest Change-I t could be i n s i g h t f u l t o i n t e g r a t e t h e present
s t a t e of e c o l o g i c a l understanding on combinations
of trend s t a t e changes i n an attempt t o s e e what a
p o s s i b l e worst-case scenario might be f o r v e g e t a t i o n
i n western coniferous f o r e s t s . The r e l a t i v e o r d e r
of s e n s i t i v i t y , conceived a s p r o b a b i l i t y of mortali t y a s s o c i a t e d with a p a r t i c u l a r environmental
s t r e s s , i s o f t e n d i f f e r e n t (even opposite) between
various s p e c i e s f o r one s t r e s s , compared t o another.
Ranking t r e e s p e c i e s of mature i n d i v i d u a l s i n terms
of l i k e l y m o r t a l i t y t o f i r e would place ponderosa
and lodgepole pine a s "low", while white f i r and
incense cedar would o f t e n be r a t e d "high". The l a t t e r would be k i l l e d by a moderate i n t e n s i t y s u r f a c e
f i r e ( n o t a prescibed burn n e c e s s a r i l y ) .
I n c o n t r a s t , research on ambient oxidant a i r
p o l l u t i o n s e n s i t i v i t y has shown ponderosa pine a s
very s e n s i t i v e , while white f i r and incense cedar
might have a low s e n s i t i v i t y t o t h i s s t r e s s . A i r
p o l l u t i o n weakens c e r t a i n t r e e s p e c i e s which a r e
subsequently h i t by b i o t i c d i s e a s e s and i n s e c t s ,
and produces a decreased competitive advantage,
compared t o l e s s s e n s i t i v e s p e c i e s . I n t h e communi t y , t h i s can lead t o decreased l o n g e v i t y of t h e
sensitive species.
A s a worst case condition, one could envision
t h a t our present western f o r e s t h e r i t a g e from p r i s t i n e decades ago under a n a t u r a l f i r e frequency
s h i f t e d t h e balance of t r e e s p e c i e s composition such
t h a t i t was h e a v i l y proportioned with what a r e now
a i r p o l l u t i o n s e n s i t i v e s p e c i e s . I f t h e a i r pollut i o n problem i n t e n s i f i e s over t h e y e a r s , t h e s e
s p e c i e s can be expected t o be decimated. The combined e f f e c t of both of t h e s e trend s t a t e changes,
each working on d i f f e r e n t t r e e s p e c i e s , micht make
it impossible t o preserve and p r o t e c t coniferous
f o r e s t s i n c e r t a i n l o c a t i o n s ( f i g . 4).
AIR 4
SENSITIVE,
FIRETOLERANT
SPECIES
ABUNDANCE
P o t e n t i a l Responses Under Multiple S t r e s s e s
Dolan and Hayden (1978) c l a s s i f i e d types of
changes i n n a t u r e r e s e r v e park ecosystems a s e i t h e r
steady s t a t e , eddy s t a t e , o r t r e n d s t a t e . Steady
s t a t e changes i n c l u d e d i u r n a l and seasonal environmental changes under which t h e system has evolved.
Eddy s t a t e changes a r e d i s c r e t e pulses of environmental d i s t u r b a n c e s . Trend s-cate changes a r e longterm changes t h a t a r e o f t e n t h e most s u b t l e t o det e c t , a s well a s t h e most d i f f i c u l t from which t o
0
v
A I R POLLUTION-TOLERANT.
FIRE- SENSITIVE SPECIES A B U N D A N C E
Figure 4--Possible f u t u r e course of f o r e s t s p e c i e s
composition under combined s t r e s s of a i r p o l l u t i o n
and n a t u r a l f i r e exclusion.
CONCLUSIONS
I n t h e c a s e of a i r p o l l u t i o n , t h e r e could be t h e
g r a d u a l e l i m i n a t i o n of many f i r e - t o l e r a n t t r e e spec i e s from f o r e s t s . Whenever a n a t u r a l f i r e does occ u r under such a f u t u r e s c e n a r i o , t h e p r o p o r t i o n
of f o r e s t s t a n d s p e c i e s i n t h e f i r e - s e n s i t i v e c a t e gory could be much h i g h e r t h a n normal, and sudden
q u a l i t a t i v e changes, o r ecosystem c a t a s t r o p h e s , i n
c o n i f e r f o r e s t s p e c i e s composition could be expected.
There i s a s t r o n g l i k e l i h o o d t h a t c o n i f e r s t a n d s
might change i n t o mixtures of deciduous t r e e and
shrub communities a t mid-elevations, and perhaps
s c r u b f i e l d ecosystems a t h i g h e r e l e v a t i o n s which
p r e s e n t l y c o n t a i n c o n i f e r f o r e s t s . This would repres e n t a q u a l i t a t i v e change from one s u c c e s s i o n a l p a t t e r n t o a n o t h e r , and i s a p o s s i b i l i t y which f o r e s t
management has a r e s p o n s i b i l i t y t o t r y t o e v a l u a t e .
Acknowledgments:
This s t u d y was funded i n p a r t with f e d e r a l funds
from t h e Environmental P r o t e c t i o n Agency under
Contract Numbers 68-03-0273, 68-03-2442, and
Grant Number R805410. The c o n t e n t of t h i s paper
i s not t o be construed a s r e p r e s e n t i n g views o r
p o l i c i e s of t h e EPA, n o r a s a concurrence of t h e
Agency with t h e r e s u l t s presented. Mention of
t r a d e names o r commercial products i n t h i s paper
does n o t c o n s t i t u t e e i t h e r an endorsement o r a
recommendation f o r t h e i r use. This paper does n o t
r e p r e s e n t EPA p o l i c y , p o s i t i o n , o r f i n d i n g s .
LITERATURE CITED
Cooper, C.F.
1961. Equations f o r t h e d e s c r i p t i o n of p a s t
growth i n even-aged s t a n d s of ponderosa pine.
For. Sci.:72-80.
Dolan, R. and B.P. Hayden.
1978. Environmental dynamics and r e s o u r c e
management i n t h e U.S. National Parks:Environ.
Manag. 2 ( 3 ) :249-258.
G r i e r , C.C., R.L. Edmonds, R.H. Waring and D.W.
Cole. 1978. F o r e s t management i m p l i c a t i o n s of
p r o d u c t i v i t y , n u t r i e n t c y c l i n g and water
r e l a t i o n s r e s e a r c h i n western c o n i f e r s . p.96106 I n : Proc., J n t Conv. of S.A.F. and Can.
I n s t . For., 1978.
K i c k e r t , R.N.
1977a. Toward f o r e c a s t i n g a l t e r n a t i v e f u t u r e
ecosystem responses: ecosystem modeling.
p.63-85 I n Photochemical A i r P o l l u t a n t E f f e c t s
on Mixed'Tonifer Ecosystems. Progress Report
1974-75. EPA-600/3-77-058.
U. S. Environmental
P r o t e c t i o n Agency,.Corvallis Environmental
Research Laboratory, C o r v a l l i s , Oregon.
K i c k e r t , R.N.
1977b. D e f i n i t i o n of t h e c o n i f e r f o r e s t ecosystem a s a group of coupled e c o l o g i c a l models.
p. 71 -1 05 I n Photochemical Oxidant A i r
P o l l u t i o n ' I T f f e c t s on a Mixed Conifer F o r e s t
Ecosystem--A Progress Report, 1976. Paul R.
M i l l e r and Michael J. Elderman, eds.
EPA-600/3-77-1 04. U. S. Environmental Protect i o n Agency, C o r v a l l i s Environmental Research
Laboratory, C o r v a l l i s , Oregon.
K i c k e r t , R.N.
1980. Ecosystem s i m u l a t i o n modeling. Chpt. 2
I n Photochemical Oxidant A i r P o l l u t i o n E f f e c t s
on a Mixed Conifer F o r e s t Ecosystem. O.C.
Taylor (ed. ) U.S. Environmental P r o t e c t i o n
Agency, Environmental Research Laboratory,
1 95 p
C o r v a l l i s , Oregon. EPA-600/3-80-002.
-
.
Smith, D.M.
1962. P r a c t i c e of S i l v i c u l t u r e . John Wiley and
Sons, New York. 578p.
U.S. Environmental P r o t e c t i o n Agency.
1978. A i r q u a l i t y c r i t e r i a f o r ozone and o t h e r
photochemical oxidants. EPA-600/8-78-004.
Volume 11. O f f i c e of Research and Development.
Washington, D.C. 341p.
U.S. Environmental P r o t e c t i o n Agency.
1979. EPA changes ozone s t a n d a r d t o 0.12 ppm.
Environmental News, January 26, O f f i c e of
P u b l i c Awareness, Washington, D.C. 3p.
S c o t t , D . J . S a l o and K.L. Reed.
Walker, R.B., D.R.M.
1972. T e r r e s t r i a l process s t u d i e s i n c o n i f e r s : a
review. pp.211-225 In: Proc., Res. on Coniferous
F o r e s t Ecosystems Symp., Bellingham, WA.
March 23-24, 1 972.
Whittaker, R.H. and W.A. Niering.
1975. Vegetation of t h e Santa Cruz Mountains,
Arizona. V. Biomass, production and d i v e r s i t y
along t h e e l e v a t i o n g r a d i e n t . Ecol. 56:771-790.
Response of Plant Communities to Air
Pollution1
R. Guderian and K. ~ u e ~ ~ e r s *
A b s t r a c t : Under t h e i n f l u e n c e of a i r p o l l u t i o n two
r e t r o g r e s s i v e p r o c e s s e s a r e s e t i n motion i n p l a n t comm u n i t i e s : By means of d i r e c t and i n d i r e c t e f f e c t s , changes occur i n s t r u c t u r e and f u n c t i o n of t h e community
l e a d i n g up t o t o t a l d e s t r u c t i o n . P a r a l l e l t o t h i s deg r a d a t i o n ( r e t r o g r e s s i o n ) i s a spontaneous o r man i n i t i a t e d process d u r i n g which t h e p r i g i n a l a d a p t i v e r e s i s t a n t members of t h e e x i s t i n g community a s w e l l a s
new a r r i v a l s undergo secondary succession. The causes
and mechanisms f o r a i r pollution-induced changes i n
p l a n t communities a r e demonstrated by means of l i t e r a t u r e a n a l y s i s and t h e i n t e r a c t i o n of dose response determining f a c t o r s a r e summarized. I n o r d e r t o emphas i z e t h e e x i s t i n g p o t e n t i a l danger and t o s e t remedial
procedures i n motion, r e s e a r c h themes a r e pointed o u t
t h a t must r e c e i v e immediate a t t e n t i o n .
Thus f a r r e s e a r c h on t h e e f f e c t s of a i r p o l l u t a n t s on p l a n t s has been c e n t e r e d on homotypi c a l p o p u l a t i o n s of economically important
s p e c i e s , With t h e development of long-term
l o a d i n g of e x t e n s i v e a r e a s e n t i r e ecosystems
a r e a l s o i n c r e a s i n g l y being i n f l u e n c e d by a i r
p o l l u t a n t s . From t h i s , t h e q u e s t i o n a r i s e s
a s t o t h e p o s s i b l e r e a c t i o n s of phytocoenoses
t o changed a i r q u a l i t y a s a new h a b i t a t f a c t o r .
c e r t a i n i n h e r e n t p a t t e r n s of t h e c o n f r o n t a t i o n
between p l a n t communities and a i r p o l l u t i o n
may be deduced.
For t h e following comparative s t u d y of t h e
i n f l u e n c e of v a r y i n g c o n c e n t r a t i o n s of a i r
p o l l u t a n t s on v e g e t a t i o n , a d i v i s i o n i n t o t h e
f o l l o w i n g l e v e l s , derived from Smith's c l a s s i f i c a t i o n (1974) seems p r a c t i c a l : h i g h , i n t e r m e d i a t e and low dosage e f f e c t s .
REACTIONS OF PLANT COMMUNITIES RELATED TO
AIR POLLUTANT CONCENTRATIONS
Single or repeated observations i n the v i c i n i t y of s i n g l e s o u r c e s a s w e l l a s w i t h i n and
o u t s i d e of extended r e g i o n s s u b j e c t e d t o a i r
p o l l u t i o n load can only provide momentary r e c o r d s o r sequences o f changes under t h e r e s p e c t i v e l o c a l c o n d i t i o n s . I n g e n e r a l , however,
~ r e s e n t e da t t h e Symposium on E f f e c t s of A i r
P o l l u t a n t s on Mediterranean and Temperate F o r e s t
Ecosystems, J u n e 22-27, 1980, R i v e r s i d e ,
C a l i f o r n i a , U.S.A.
2 ~ e s p e c t i v e l y ,Biowissenschaften, Universi-
t a t Essen, Gesamthochschule, 4300 Essen 1,
West Germany
High P o l l u t i o n Dosage
A c h a r a c t e r i s t i c of t h e r e l a t i o n s h i p between high dosage and t h e r e a c t i o n of a p l a n t
community is a breakdown of community s t r u c ture
more o r l e s s obvious depending on t h e
complexity of t h e ecosystem. The d e g r a d a t i o n
of t h e system is c h a r a c t e r i z e d by a r a p i d change
i n s t r u c t u r e , i n c l u d i n g composition. It is
accompanied and f i n a l l y r e p l a c e d by a seconda r y s u c c e s s i o n which can lead t o a new e q u i l ibrium under s u s t a i n e d load.
D i r e c t a c u t e and c h r o n i c i n j u r y appearing
e s p e c i a l l y on l e a v e s , b u t n o t always c o r r e l a t e d w i t h t h e i r p o l l u t a n t c o n t e n t , (Guderian,
1970; Linzon, 1979) w i l l f i r s t a f f e c t t h e most
s e n s i t i v e s p e c i e s of t h e t r e e s t r a t u m i n a
f o r e s t and can l e a d t o t h e t o t a l d e s t r u c t i o n of
t h e canopy. Without p r o t e c t i o n from t h e f r e e l y
--
e n t e r i n g a i r masses of p o l l u t e d a i r (Bennett and
H i l l , 1975) s h r u b , h e r b and moss o r l i c h e n l a y e r s a r e d e s t r o y e d one a f t e r a n o t h e r , u n t i l a
b a r r e n zone r e s u l t s (Gordon and Gorham, 1963;
Woodwell, 1970). As an example of such condit i o n s , t h e z o n a t i o n under t h e i n f l u e n c e of approximately 10 t o n s of SO2 per day from an i r o n
o r e r o a s t i n g f u r n a c e i n B i e r s d o r f (Germany) w i l l
be d e s c r i b e d b r i e f l y .
The denuded zone i n t h e immediate v i c i n i t y of
t h e emission s o u r c e i s surrounded by t h e t r a n s i t i o n zone w i t h i s o l a t e d c l u s t e r s of g r a s s (Deschampsia f l e x u o s a ) and r e s i s t a n t ground c o v e r
( E r i c a c i n e r e a , Galium mollugo, Veronica o f f i c i n alis, Rumex a c e t o s a , and C o n v a l l a r i a m a j a l i s )
Now and t h e n one a l s o e n c o u n t e r s t h e r e l a t i v e l y
r e s i s t a n t Sambucus racemosa and Rhamnus f r a n g u l a
i n t h i s zone. I n t h e g r a s s cover of v e g e t a t i o n
c o n s i s t i n g mostly of Deschampsia f l e x u o s a t h e
f i r s t s h o o t s of Quercus p e t r a i a a r e e s t a b l i s h e d
i n t h e s h e l t e r of t h e herbaceous v e g e t a t i o n .
The p o p u l a t i o n s of t h i s oak and Fagus s i l v a t i c a
which a d j o i n t h e s t u n t e d f o r e s t zone show
s i g n s of d i s i n t e g r a t i o n s t a r t i n g a t t h e p e r i phery. As SO2 l o a d i n g d e c r e a s e s t h e s p e c i e s
d i v e r s i t y increases, u n t i l f i n a l l y i t reaches
t h e combination t y p i c a l f o r t h e a c i d i c s o i l mixed f o r e s t (Fago-Quercetum).
A comparison w i t h o t h e r s t u d i e s (Treshow,
1968; Smith, 1974; M i l l e r and McBride, 1975;
and, Linzon, 1978) shows t h a t t h i s i s t h e typi c a l p i c t u r e of t h e break-down of a p l a n t community, t h a t i s , a change i n s p e c i e s composition
toward a s i m p l i f i c a t i o n of t h e system. I n
p r i n c i p l e i t does n o t d i f f e r from t h a t caused
by gamma r a d i a t i o n (Woodwell, 1963, 1970).
The secondary s u c c e s s i o n which s e t s i n a s soon
a s t h e o r i g i n a l v e g e t a t i o n b e g i n s t o change
l e a d s i n time under c o n s t a n t l o a d i n g t o t h e
f o r m a t i o n of new, l e s s complex s t a b l e s t r u c t u r e s .
Thus, i n an o l d manufacturing d i s t r i c t of Upper
S i l e s i a (Poland), i n l o c a t i o n s once stocked w i t h
n a t i v e c o n i f e r o u s o r mixed deciduous f o r e s t s ,
Wolak (1977 and 1979) d e s c r i b e d a s t a b l e zona t i o n i n r e l a t i o n t o d i f f e r e n t l o a d s of S02,
z i n c , and l e a d . Under heavy l o a d s an i n d u s t r i a l
w a s t e l a n d i s followed by a g r a s s zone w i t h
a s s o c i a t i o n s dominated by Deschampsia f l e x u o s a
on o l i g o t r o p h i c sand, by C a l a m a g r o s t i s e p i g e i o s
on mesotrophic s i t e s , and by C a l a m a g r o s t i s
l o s a on damp o r g a n i c s o i l . I n t h e a d j a c e n t
shrub zone one f i n d s b o t h c u l t i v a t e d and v o l u n t e e r s c r u b t r e e s p e c i e s . I t i s remarkable
t h a t P i n u s s i l v e s t r i s can t a k e on t h e shape of
a c r e e p i n g shrub o r of a t r e e w i t h b r a n c h e s
p r o j e c t i n g h o r i z o n t a l l y up t o 5 m from t h e
stem. These dwarf forms a r e no more than 2 m
h i g h a t an age of 30 t o 50 y e a r s . On low g r a d e
sands g r o u p s of t h e d e s c r i b e d P i n u s s i l v e s t r i s
forms and Solanum dulcamara were found which
were n o t found i n s i m i l a r l o c a t i o n s w i t h o u t
t h e s t r o n g i n f l u e n c e of a i r p o l l u t i o n . Those
p l a n t communities a r e c a l l e d i n d u s t r i o - c l i m a x
communities (Wolak, 1971). They r e p r e s e n t spontaneous a s s o c i a t i o n s w i t h r e l a t i v e l y c o n s t a n t
s p e c i e s composition which have developed gradu a l l y through i n d u s t r i o g e n o u s (secondary)
.
a-
s u c c e s s i o n , b o t h from s p e c i e s p r e s e n t b e f o r e
p o l l u t a n t l o a d i n g a s w e l l a s from new a r r i v a l s ,
under t h e combined i n f l u e n c e of t h e h a b i t a t
f a c t o r s ; c l i m a t e , s o i l , i n s e c t s and p a r a s i t e s - dominated by t h e f a c t o r a i r p o l l u t i o n .
I n t e r m e d i a t e P o l l u t i o n Dosage
I n t e r m e d i a t e a i r p o l l u t i o n dosage c o n d i t i o n s
a r e e c o l o g i c a l l y s i g n i f i c a n t because t h e i r subt l e , d i r e c t and i n d i r e c t e f f e c t s on t h e i n d i v i d u a l s p e c i e s can s e t t h e s t a g e f o r changes i n
t h e s t r u c t u r e of t h e community w i t h p o s s i b l y irr e v e r s i b l e consequences. I n p l a n t communities
e x p e r i e n c i n g i n t e r m e d i a t e p o l l u t i o n dosage, i n t e r r u p t i o n of growth and r e p r o d u c t i o n p r o c e s s e s
a s w e l l a s impairment of t h e v i t a l i t y o f i n d i v i d u a l p l a n t s , among o t h e r f a c t o r s through i n c r e a s e d v u l n e r a b i l i t y t o a b i o t i c and b i o t i c
s t r e s s , become p a r t i c u l a r l y important (Wentzel,
1965; Huttunen, 1979; and Laurence, 1980).
I n p i n e and s p r u c e p o p u l a t i o n s i n t h e Lower
Main Region (Germany), which indeed show an i n creased sulfur content i n the leaves, but did
n o t y e t d i s p l a y an abnormal l o s s o f i n d i v i d u a l s ,
morphological changes such a s t h i n crowns coupl e d w i t h s h o r t e r n e e d l e s were d e t e c t e d i n o l d e r
s t a n d s (Wentzel, 1979). Such changes occur slowl y and o n l y t h e accumulation of annual e f f e c t s
g r a d u a l l y l e a d s t o h i g h e r m o r b i d i t y (Wentzel,
1980). I n t h i s c o n t e x t t h e c a r r y - o v e r of accumulated t o x i c a n t s i n t h e new s h o o t s o f t h e
n e x t growing season should b e mentioned ( K e l l e r ,
1978; P r e s t o n , 1979). A s l i g h t change of t h e
h o r i z o n t a l s t r u c t u r e i n t h e canopy w i l l i n f l u ence such h a b i t a t f a c t o r s a s t h e s u p p l y of l i g h t
and p r e c i p i t a t i o n f o r t h e lower-lying v e g e t a t i o n .
F r e q u e n t l y , t h e i n t e r a c t i o n of changed s o i l r e action--pH--and t o x i c a n t c o n t e n t b r i n g s about
a r e s t r u c t u r i n g of t h e shrub and h e r b s t r a t a
o v e r extended a r e a s sometimes i n f l u e n c i n g nat u r a l r e p r o d u c t i o n of woody s p e c i e s (Lux, 1964;
Wentzel, 1971; Harward and Treshow, 1975)
Such changes i n t h e composition of p l a n t
communities were d e t e c t e d through v e g e t a t i o n
surveys caused by a complex of f a c t o r s . F o r
example, c e r t a i n s p e c i e s were found i n d e n s e
c l u s t e r s , w h i l e o t h e r s were e v e n l y d i s t r i b u t e d
and s t i l l o t h e r s were t o t a l l y a b s e n t , dependi n g on dosage (Borgsdorf, 1960; Gordon and
Gorham, 1963; N i k l f e l d , 1967; Ionescu, e t a l . ,
1971; Trautmann, e t a l . , 1971). Hajduck (1961)
t a l k s about p o s i t i v e o r n e g a t i v e p h y t o i n d i c a t o r s ,
w h i l e Anderson (1966, quoted i n Treshow 1968)
employs t h e terms " i n c r e a s e r " o r " d e c r e a s e r 'I
The concept of p h y t o i n d i c a t o r s i s e s s e n t i a l l y
t h e same a s b i o i n d i c a t i o n w i t h l i c h e n o r moss
s p e c i e s (Le Blanc and Rao, 1975; Taoda, 1977;
and P i l e g a a r d , 1978). K a l e t a (1972) was a b l e
t o demonstrate i n a d d i t i o n t h e dynamics of
change of whole p l a n t a s s o c i a t i o n s under t h e
i n f l u e n c e of magnesite.
Brandt and Rhoades (1972, 1973) took t r e e
s p e c i e s of s e v e r a l s t r a t a i n t o c o n s i d e r a t i o n
i n t h e i r s t u d y on t h e i n f l u e n c e of l i m e s t o n e
d u s t on a f o r e s t community. T h i s method made
.
i t p o s s i b l e t o a s s e s s t h e t r e n d of f u t u r e succ e s s i o n , e s p e c i a l l y through s h i f t s d e t e c t e d
i n t h e s p e c i e s d i v e r s i t y of t h e s e e d l i n g and
s p r o u t d a t a . Thus, Quercus c o c c i n e a , Quercus
v e l u t i n a o r T i l i a americana oan drop o u t a s
members of t h e oak-chestnut a s s o c i a t i o n and
L i r i o d e n d r o n t u l i p i f e r a , & saccharinum
and p o s s i b l y Quercus muehlenbergii could become dominant s p e c i e s . Through t h i s example i t
a l s o becomes e v i d e n t how a i r p o l l u t a n t s can
i n f l u e n c e t h e makeup of phytocoenoses by i n f l u e n c i n g r e p r o d u c t i o n (Wentzel, 1963; Karnoskv,
and S t a i r s , 1974; K e l l e r , 1976).
McClenahen (1978) u t i l i z e d community compo s i t i o n a s a means t o i n v e s t i g a t e changes i n
p l a n t communities a l o n g a p o l l u t i o n g r a d i e n t
i n t h e Ohio V a l l e y (USA). I n t h i s s t u d y , a n
e a s t e r n deciduous f o r e s t e x p e r i e n c i n g intermed i a t e dosages was shown t o d e c l i n e i n s p e c i e s
r i c h n e s s , evenness, and Shannon d i v e r s i t y i n dex w i t h i n a l l s t r a t a of t h e community, p a r t i c u l a r l y i n those locations experiencing t h e
h i g h e s t r e l a t i v e dose. Simultaneously, t h e
s i m i l a r i t y i n composition d e c r e a s e d w i t h i n c r e a s i n g dosage. Thus, t h e r e l a t i v e importance
of
saccharinum, a s p e c i e s s l i g h t l y s t i m u l a t e d by l i m e s t o n e d u s t (Brandt and Rhoades,
1972), showed d i s t i n c t d e c l i n e i n a l l s t r a t a ,
w h i l e t h e importance of Aesculus o c t a n d r a i n c r e a s e d . Opposing t e n d e n c i e s i n d e n s i t y were
observed i n some s t r a t a . A d e c l i n e i n t h e t r e e
and h e r b s t r a t a was accompanied by a n i n c r e a s e
of t h e subcanopy and t h e s h r u b s t r a t a . This
can be a t t r i b u t e d t o b e t t e r l i g h t c o n d i t i o n s i n
t h e lower s t r a t a combined w i t h a r e l a t i v e i n c r e a s e of h e r b s i n t o l e r a n t t o shade.
Low P o l l u t i o n Dosage
The e f f e c t s of low dosages on v e g e t a t i o n l i e
i n t h e b o r d e r zone between t h e f l u c t u a t i n g
s t a t e s of normal, i . e . , u n a f f e c t e d v e g e t a t i o n
on t h e one hand, and s i g n i f i c a n t i n j u r i o u s e f f e c t s on t h e o t h e r hand. Depending upon t h e
r e s p e c t i v e p o l l u t a n t , i t s c o n c e n t r a t i o n and
d u r a t i o n of a c t i o n , a s w e l l a s t h e a f f e c t e d obj e c t and t h e l o c a l c o n d i t i o n s , t h e s e e f f e c t s
can r a n g e from i n c r e a s e s t o r e d u c t i o n s i n growth,
r e p r o d u c t i v e c a p a b i l i t y o r q u a l i t y of p l a n t s .
Under p r a c t i c a l c o n d i t i o n s such e f f e c t s can be
d e t e c t e d t o o n l y a c e r t a i n d e g r e e of t h e a c t u a l
i n t e n s i t y . The d e t e c t i o n l i m i t h a s been lowe r e d through t h e development of new exposure
systems w i t h f i l t e r e d and u n f i l t e r e d a i r (Mandl,
e t a l . , 1973; Lee, e t a l . , 1973; M i l l e r , e t a l . ,
1979; Shinn, e t a l . , 1979). However, measurement of p o l l u t a n t e f f e c t s on p l a n t communities
occupying l a r g e r e g i o n s p r e s e n t s p a r t i c u l a r
d i f f i c u l t i e s because t h e n e c e s s a r y p o l l u t i o n f r e e c o n t r o l a r e a s w i t h comparable s o i l and
climate a r e not available.
Before d e t e c t a b l e r e d u c t i o n s occur i n prod u c t i v i t y o r a l t e r a t i o n of environmental cond i t i o n s c a n b e observed, t h e r e a r e v a r i o u s
changes t h a t a r e induced a t t h e p l a n t biochemi c a l , physiological o r substructural l e v e l
( K e l l e r , 1974; J a g e r and K l e i n , 1977; Horsman
and Wellburn, 1977; and, Raabe and Kreeb, 1979).
Of c o u r s e t h e q u e s t i o n of how much such f i n d i n g s r e v e a l a b o u t t h e economic and e c o l o g i c p e r formance of a p a r t i c u l a r p l a n t s p e c i e s remains
of c e n t r a l importance h e r e . Some of t h e r e a c t i o n s undoubtedly have no e f f e c t s on t h e t o t a l
organism; even i f s i g n i f i c a n t e f f e c t s a r e found,
it is very d i f f i c u l t t o e s t a b l i s h a causal l i n k
t o t h e primary r e s p o n s e s mentioned above. The
p o s s i b l e e f f e c t s of low dosage on p l a n t comm u n i t i e s , f o r example, through changes i n i n t e r s p e c i f i c competition, a r e almost t o t a l l y
unresolved. The f i l t e r i n g e f f e c t s of v e g e t a t i o n
i s a n important p r o c e s s b u t t h i s t o p i c w i l l
only be introduced h e r e .
A s shown i n t h e S o i l i n g p r o j e c t ( U l r i c h , e t
a l . , 1978) o r t h e Hubbard Brook s t u d y (Bormann
and Likens, 1979) v e g e t a t i o n can f i l t e r l a r g e
amounts of p o l l u t a n t s o u t of t h e atmosphere
w i t h o u t showing s i g n s of e x t e r n a l i n j u r y o r
growth d e p r e s s i o n . P a r t i c u l a t e and gaseous
p o l l u t a n t s e n t e r a n ecosystem through a d s o r p t i o n and a b s o r p t i o n mainly on l e a f s u r f a c e s a s
w e l l a s s o i l and w a t e r s u r f a c e s ( H i l l , 1971;
Bennett and H i l l , 1975; and, Olsen, 1976). The
s p e c i f i c behavior of t h e s u b s t a n c e i s i m p o r t a n t
f o r t h e p o s s i b l e long-term e f f e c t s of low do-,
s a g e on p l a n t communities. P o l l u t a n t s which a r e
s u b j e c t t o r a p i d decomposition such a s ozone
o r PAN t a k e e f f e c t through t h e summation of
d i r e c t e f f e c t s . NOx, NH3, o r s u l f u r compounds
can be channeled i n t o t h e n u t r i e n t c y c l e and
may d e s t r o y t h e b a l a n c e of e s p e c i a l l y s e n s i t i v e
ecosystems, such a s moors, through e u t r o p h i c a t i o n ( P o r t e r , e t a l . , 1972; Cowling and Locky e r , 1976). The importance of a c i d p r e c i p i t a t i o n
i n t h i s c o n t e x t i s n o t y e t c l e a r (Braekke, 1976;
and, T a m , 1976). Accumulating s u b s t a n c e s such
a s heavy m e t a l s , r e p r e s e n t a s p e c i a l danger f o r
ecosystems (Kraemer, 1976; and Guderian, 1980).
S o i l samples and a n a l y s e s of moss specimens have
r e v e a l e d t h a t a c o n s t a n t i n p u t i n t o ecosystems
i s o f f s e t by o n l y a l i m i t e d e x p o r t , and t h a t
t h i s i s now o c c u r r i n g over wide a r e a s (Huckabee,
1973; Ruhling and T y l e r , 1973; and Grdzinska,
1978). Such components can a l s o endanger t h e
n u t r i e n t c y c l e (Mags, 1977 and Uba, 1977);
f u r t h e r , t h e y r e d u c e t h e number and a c t i v i t y
of decomposers, t h e r e b y i m p a i r i n g r e m i n e r a l i z a t i o n a s a requirement f o r u n i n t e r r u p t e d b i o geochemical c y c l e s ( T a y l o r , 1975; and, G r e s z t a ,
e t a l . , 1979). E s p e c i a l l y , w i t h accumulating
s u b s t a n c e s and under continuous l o a d i n g , it i s
only a q u e s t i o n of time b e f o r e t h e d i r e c t and
i n d i r e c t e f f e c t s d e s c r i b e d above begin t o i n t e r r u p t t h e s t r u c t u r e and f u n c t i o n of p l a n t
communities.
THE INFLUENCE OF POLLUTANTS ON THE
FUNCTION OF PLANT COMMUNITIES
Changes i n p l a n t communities caused by p o l l u t a n t s can l e a d t o more o r l e s s l a s t i n g impairment of economic and e c o l o g i c f u n c t i o n s depending on t h e dosage. The damage t o a g r i c u l t u r e
through growth r e d u c t i o n , l o s s of q u a l i t y and
h i g h e r l a b o r c o s t s have long drawn c o n s i d e r a b l e a t t e n t i o n , b u t only now i s an a t t e m p t being made t o t a k e t h e e f f e c t s on performance
of ecosystems i n t o account. I n t h i s connect i o n , an e s p e c i a l l y important q u e s t i o n i s how
p o l l u t a n t s a f f e c t such f u n c t i o n s of v e g e t a t i o n
a s f i l t e r e f f e c t , s t a b i l i z a t i o n of c l i m a t e ,
r e g u l a t i o n of water and n u t r i e n t c y c l e s , s o i l
c o n s e r v a t i o n a s w e l l a s t h e p r e s e r v a t i o n of
l i v i n g space f o r polymorphic zoo- and phytoceonoses. Extensive changes i n v e g e t a t i o n
cover a r e probably l i n k e d t o i n t e r r u p t i o n o r
even t o t a l breakdown of a l l t h e above-mentioned f u n c t i o n s . For example, t h e f u n c t i o n
of p l a n t communities a s p r o t e c t i o n a g a i n s t
erosion o r a s a f a c t o r i n counter balancing
e x c e s s i v e temperature f l u c t u a t i o n s and t h e
accompanying danger from l i g h t f r o s t d u r i n g
bud b r e a k i s c o n s i d e r a b l y more impaired i n
a r e a s experiencing h i g h p o l l u t a n t dosage where
woods have been r e p l a c e d by s p a r s e v e g e t a t i o n
than i n unpolluted a r e a s . C u r r e n t l y , t o what
e x t e n t i n t e r m e d i a t e and low dosages a f f e c t
t h e f u n c t i o n s of v e g e t a t i o n mentioned, can,
a t b e s t , b e deduced t o an o r d e r of magnitude
(Materna, 1980) from t h e known r e a l e f f e c t s on
vegetation.
Causes f o r t h e Observed Responses
of P l a n t Communities
The e f f e c t s of a given p o l l u t a n t on p l a n t
communities, a s i l l u s t r a t e d by s e v e r a l examp l e s , a r e determined by: t h e g e n e t i c a l l y predetermined d e g r e e of r e s i s t a n c e of t h e companion s p e c i e s (Dochinger e t a l . , 1965; Rohmeder
e t a l . , 1965), t h e modifying i n f l u e n c e of environmental c o n d i t i o n s of r e s i s t a n c e , and t h e
changes i n i n t r a - and i n t e r s p e c i f i c r e l a t i o n s
caused by p o l l u t a n t s .
P o p u l a t i o n s of c e r t a i n p l a n t s p e c i e s , var i e t i e s , and c l o n e s , a s w e l l a s i n d i v i d u a l s
w i t h i n t h e r e s p e c t i v e populations s t u d i e d ,
r e a c t t o a given a i r p o l l u t i o n s t r e s s w i t h
v a r y i n g d e g r e e s of s e n s i t i v i t y . I n c o n t r a s t
t o c e r t a i n phytopathogenic organisms (Baumann,
1951; Grossmann~1970), t h e r e i s no a b s o l u t e
r e s i s t a n c e , a s demonstrated by t h e e x i s t e n c e
of v e g e t a t i o n - f r e e zones. The schematic
diagram (Figure 1 ) i s an a t t e m p t t o demonstrate
which f a c t o r s i n f l u e n c e t h e response t o a i r
pollution stress.
I n d i v i d u a l and S p e c i e s S p e c i f i c Responses
According t o L e v i t t (1972), two mechanisms
determine a p l a n t ' s r e s i s t a n c e t o s t r e s s :
s t r e s s avoidance and s t r e s s t o l e r a n c e . I n
t h e f i r s t c a s e t h e s t r e s s , caused h e r e by a
s p e c i f i c p o l l u t a n t dose, i s prevented from
t a k i n g e f f e c t - - i t i s excluded. A m u l t i t u d e
of f a c t o r s determines t h e r e s i s t a n c e of a
p l a n t organism t o t h e e n t r y of p o l l u t a n t s i n t o
t h e c e l l . Morphological p r o p e r t i e s such a s
shape and s u r f a c e s t r u c t u r e i n c l u d i n g wax
l a y e r s ( R e n t s c h l e r , 1973; S h r i n e r , 1980) a s
w e l l a s t h e number, d i s t r i b u t i o n , and a p e r t u r e
of t h e stoma (Meidner and Mansfield, 1968)
must be mentioned. According t o Taylor (1978),
whose d e f i n i t i o n was taken i n t o c o n s i d e r a t i o n
i n t h e corresponding s e c t i o n of F i g u r e 1,
s t r e s s t o l e r a n c e presupposes t h e e n t r y of t h e
r e s p e c t i v e p o l l u t a n t i n t o t h e c e l l . As long
a s t h e e n t e r i n g substance i s t o l e r a t e d , a s s i m i l a t e d o r b u f f e r e d , and consequently no
morphological o r p h y s i o l o g i c a l change t a k e s
p l a c e , one speaks of " s t r a i n avoidance." Above
c e r t a i n i n t r a c e l l u l a r concentrations, for
example, a f t e r c e r t a i n biochemical t h r e s h o l d
v a l u e s have been exceeded, i n j u r y o c c u r s which
i s e i t h e r r e v e r s i b l e ( e l a s t i c s t r a i n ) , such
a s s u b t l e changes i n p h o t o s y n t h e t i c performance
( S i j and Swanson, l 9 7 4 ) , o r i r r e v e r s i b l e ( p l a s t i c s t r a i n ) , such a s i n j u r y t o l e a v e s i n t h e
form of n e c r o s i s .
Thus, t h e biochemical t h r e s h o l d v a l u e s ,
which c h a r a c t e r i z e t h e t r a n s i t i o n s from s t r a i n
avoidance t o s t r a i n t o l e r a n c e a s w e l l a s from
e l a s t i c s t r a i n t o p l a s t i c s t r a i n , determine
t h e t o l e r a n c e of a p l a n t . It follows t h a t t h e
i n d i v i d u a l response can m a n i f e s t i t s e l f i n
terms of i n d i f f e r e n c e , m o d i f i c a t i o n o r d e a t h
of t h e a f f e c t e d p l a n t depending on t h e l e v e l
of ambient s t r e s s , and t h e r e s p e c t i v e r e s i s t a n c e .
As i s a p p a r e n t from F i g u r e 1, a m u l t i t u d e of
organismal and environmental f a c t o r s b e f o r e ,
d u r i n g , and a f t e r t h e p o l l u t a n t impact i s r e s p o n s i b l e f o r t h e sometimes v e r y g r e a t d i f f e r e n c e s i n t h e " r e s i s t a n c e s e r i e s " o r "res i s t a n c e groups" of v a r i o u s a u t h o r s ( S t o k l a s a ,
1923; Bredemann, 1956; Thomas, 1961; Garber,
1967; Mooi, 1974; Davis and Wilhour, 1976;
Guderian, 1977). A l l c l i m a t i c f a c t o r s , f o r
example, t h a t r e g u l a t e t h e number, s i z e and
a p e r t u r e of t h e stomata (Bronte and Conguet,
1975; H a l l and Kaufmann, 1975), such a s l i g h t ,
optimal water supply, h i g h r e l a t i v e humidity
o r adequate temperature, determine t h e r a t e
a t which p o l l u t a n t s a r e absorbed (Guderian,
1970; Jones and Mansfeld, 1970; McLean and
Schneider, 1971).
The i n f l u e n c e of edaphic f a c t o r s i s demons t r a t e d w i t h two examples: Copper-beech (Fagus
s i l va t i c a ) i s c o n s i d e r a b l y more r e s i s t a n t on
s o i l s w i t h high lime c o n t e n t than on sandy
s o i l low i n n u t r i e n t s ; elm (Ulmus c a m p e s t r i s )
proved t o b e one of t h e most r e s i s t a n t s p e c i e s
i n a l l u v i a l forests, but i n l e s s suitable
h a b i t a t s i t was one of t h e most v u l n e r a b l e
of a l l t h e deciduous s p e c i e s (Wentzel, 1968).
T h i s shows t h e d i f f i c u l t y i n s e t t i n g up genera l l y accepted r e s i s t a n c e s e r i e s , a s r e c e n t
s t u d i e s w i t h v a r i o u s soybean c u l t i v a r s under
changing environmental c o n d i t i o n s have c l e a r l y
shown (Heagle, 1979a, b ) .
The l a r c h s e r v e s a s a t y p i c a l example f o r
changes i n r e s i s t a n c e i n r e l a t i o n t o l e v e l s
of c o n c e n t r a t i o n (Guderian and Stratmann, 1962;
Wentzel, 1963). Under h i g h , a c u t e SO2 conc e n t r a t i o n s , both L a r i x europea and L a r i x
l e p t o l e p i s show s i g n s of n e c r o s i s b e f o r e spruce
-
momentary
low
dosage
intermediate high
momentary
..
I
air oollution stress
momentary
succession momentary interspecific relationship
areal and
areal and abundance. alteration
alteration low dosage response intermediate dosage response high dosage response
no significant
alteration of
plant communities
first alterations in
extensive simplification structure and compositions up to total destruction of plant communities
of plant communities Figure 1: Effect-determining-factors'for various responses of plants on individual-, species- and community-levels. ( P i c e a a b i e s ) and p i n e (Pinus s i l v e s t r i s ) . On
t h e o t h e r hand, t h e l a r c h i s among t h e most
r e s i s t a n t c o n i f e r s under continuous low l e v e l s
of c o n c e n t r a t i o n (Wentzel, 1963), and i t i s
widely used t o r e e s t a b l i s h t r e e p o p u l a t i o n s
a f t e r t h e d e g r a d a t i o n of spruce and p i n e f o r e s t s i n r e g i o n s of c h r o n i c s t r e s s .
Regarding organismal f a c t o r s , t h e s i g n i f i cance of age f o r s e n s i t i v i t y should be s t r e s s e d .
According t o o b s e r v a t i o n i n t h e f i e l d , c o n i f e r s
such a s P i c e a a b i e s and P i n u s s i l v e s t r i s r e main p a r t i c u l a r l y s u s c e p t i b l e from t h e l a t e
p o l e timber s t a g e ( a t t h e time of accumulating
growth) through t o t h e t r e e timber s t a g e . Duri n g t h e s e p e r i o d s of development, e s p e c i a l l y
s t r o n g r e d u c t i o n s i n growth and t h e widespread
d e g r a d a t i o n of e n t i r e s t a n d s occur (Wentzel,
1962; Materna e t a l . , 1969), w h i l e deciduous
p o p u l a t i o n s respond i n a much weaker form. I n
p l a n t i n g s , however, under mostly c h r o n i c SO2
c o n c e n t r a t i o n s , t h e c o n i f e r s mentioned and t h e
copper-beech (Fagus s i l v a t i c a ) and pedunculate
oak (Quercus pedunculata) e x h i b i t e d n e a r l y
e q u a l r e s i s t a n c e (Guderian and Stratmann, 1968).
One a s p e c t n o t o f t e n taken i n t o account when
judging t h e r e s i s t a n c e of p l a n t s , b e s i d e s environmental, p o l l u t a n t , and o r g a n i c i n f l u e n c e s ,
i s t h e c r i t e r i a used t o i n t e r p r e t t h e e f f e c t .
Various deciduous t r e e s p e c i e s , such a s l i n d e n
( T i l i a c o r d a t a an& T i l i a p l a t y p h l l o s ) and beech
(Fagus s i l v a t i c a ) respond t o a c u t e SO2 conc e n t r a t i o n s w i t h l e a f n e c r o s i s e a r l i e r than
s p r u c e (Picea a b i e s ) o r S c o t s p i n e (Pinus s i l v e s t r i s ) . N e v e r t h e l e s s t h e deciduous s p e c i e s
can s t i l l grow i n p o l l u t e d r e g i o n s where spruce
and S c o t s p i n e d i e o u t (Wentzel, 1968). Thus
r e s i s t a n c e must f i r s t of a l l b e c h a r a c t e r i z e d
by t h e d i f f e r e n c e s i n t h e r e d u c t i o n of growth
and y i e l d of t h e s p e c i f i c s p e c i e s . The funct i o n s of t h e p l a n t s p e c i e s being considered
h e r e determine t h e c r i t e r i a used t o e v a l u a t e
t h e e f f e c t s (Guderian, 1977). Through t h e
s h o r t d e s c r i p t i o n of f a c t o r s determining t h e
r e s i s t a n c e of a n i n d i v i d u a l o r a s p e c i e s i t
can b e seen what d e g r e e s of v a r i a t i o n must be
expected i n t h e responses. The use of t h e s e
r e s u l t s t o f o r e c a s t t h e behavior of s i n g l e
s p e c i e s under a i r p o l l u t i o n s t r e s s i s n e c e s s a r i l y v e r y d i f f i c u l t , e s p e c i a l l y when s t u d y i n g
p l a n t communities.
I n t h e following model, supported by experi m e n t a l r e s u l t s , an a t t e m p t i s made t o i l l u s t r a t e t h e p o s s i b l e responses of two p l a n t
species t o increasing a i r pollution s t r e s s
(Fig. 2 ) . A s p e c i f i c response of two p l a n t
s p e c i e s (A and B) i s shown i n p e r c e n t of cont r o l . Up t o a s p e c i f i c c o n c e n t r a t i o n l a b e l e d
A 1 and B3 no s i g n i f i c a n t d e v i a t i o n i n t h e r e sponses of t h e exposed p l a n t s and t h e c o n t r o l
p l a n t s could b e d e t e c t e d . Important q u a l i t a t i v e d i f f e r e n c e s i n response between t h e two
s p e c i e s e x i s t above c o n c e n t r a t i o n A1
With
Species A, t h e s p e c i f i c response i s i n i t i a l l y
s t i m u l a t e d by sulphur d i o x i d e ; a r e d u c t i o n of
performance o n l y occurs a t a h i g h e r concentrat i o n , w h i l e t h i s Species B l a c k s s t i m u l a t i n g
e f f e c t . The f u r t h e r s l o p e of t h e c u r v e shows
.
t h e degree of r e d u c t i o n i n response. The
c o n c e n t r a t i o n A 4 / ~ 4should be emphasized, a s
h e r e t h e r e s i s t a n c e r e l a t i o n s h i p of t h e two
s p e c i e s changes (Wentzel, 1963). I n t h e conc e n t r a t i o n range A1 t o A 4 / ~ 4s p e c i e s A would
have an advantage over s p e c i e s B, even under
p o l l u t a n t c o n c e n t r a t i o n s which do n o t y e t
have a n adverse e f f e c t on s p e c i e s B. Accordi n g l y , changes i n t h e composition of p l a n t
communities must be expected even i f SO2 conc e n t r a t i o n s a r e s o low t h a t they do not y e t
have a d i r e c t harmful e f f e c t . This i s a
s i g n i f i c a n t aspect f o r ecological research.
Community S p e c i f i c Responses
The p r e v i o u s l y demonstrated r e l a t i o n s h i p s
between h e r e d i t y , environment and r e s i s t a n c e
i n i n d i v i d u a l s o r homotypical p o p u l a t i o n s a r e
n a t u r a l l y a l s o v a l i d f o r p l a n t communities.
Community s p e c i f i c a s p e c t s must be given add i t i o n a l c o n s i d e r a t i o n when a s c e r t a i n i n g p o l l u t a n t e f f e c t s . The importance of t h e r e l a t i o n s h i p between two o r more p o p u l a t i o n s
shown i n F i g . 1 i s underlined by t h e few exi s t i n g r e s u l t s from experiments on t h e i n f l u ence of a i r p o l l u t a n t s t o p l a n t communities.
Thus, according t o experimental a n a l y s i s of
pure and mixed seedings, c o n s i s t i n g of r y e
g r a s s (Lolium multiflorum) h a i r y v e t c h (Vicia
v i l l o g a ) and crimson c l o v e r ( T r i f o l i u m i n c a r natum) s h i f t s i n t h e composition of p l a n t comm u n i t i e s cannot b e explained e x c l u s i v e l y through
t h e d i r e c t e f f e c t of p o l l u t a n t s on v a r i o u s
s p e c i e s of d i f f e r e n t s e n s i t i v i t y (Guderian,
1966, 1977). Under SO2 t h e i n f l u e n c e of i n t e r s p e c i f i c competition was a l t e r e d . As a r e s u l t ,
t h e primary e f f e c t on t h e more s u s c e p t i b l e memb e r s was magnified t o such a degree t h a t they
could no longer compete e f f e c t i v e l y f o r v i t a l
growth-determining f a c t o r s . As a r e s u l t of
changed competition i n t h e community, t h e
d e c l i n e of t h e more s e n s i t i v e members allowed
improved growth of t h e more r e s i s t a n t s p e c i e s .
The t o t a l community y i e l d decreased l e s s than
would have been expected from t h e l o s s of
t h e more s u s c e p t i b l e s p e c i e s . S i m i l a r r e s u l t s
were found under t h e i n f l u e n c e of ozone (Bennett
and Runeckles, 1977), u l t r a v i o l e t r a d i a t i o n
(Fox and Caldwell, 1978) and i o n i z i n g r a d i a t i o n
(McCormick, 1963). The l a s t of t h e s e s t u d i e s
shows t h e importance of s t r e s s d u r i n g t h e seedl i n g and s p r o u t s t a g e s .
The e x t e n t of s h i f t s i n p l a n t communities a s
a r e a c t i o n t o a given load i s a l s o dependent
t o a l a r g e degree on t h e c o n d i t i o n of t h e community i t s e l f . The importance of t h e b u i l d i n g
of s t r a t a , of morphological s t r u c t u r e s , a s w e l l
a s r e l i e f and uniformity of t h e v e g e t a t i o n cover
were a l r e a d y pointed o u t a s was t h e i n t e r c o n n e c t i o n between s t a g e s of succession and system
responses. The s t a b i l i t y of a community g r e a t l y i n f l u e n c e s t h e response of i t s i n d i v i d u a l
members a s w e l l a s t h e whole t o a given p o l l u t a n t load. I n t h e presence of small d i s t u r b a n c e s ,
h i g h l y productive, complex systems can u s u a l l y
Special responses of
p l a n t species A and B
control = 100%
Typical reactions of two p l a n t species d e p e n d i n g
on t h e s u l f u r dioxide content of a i r
r e g a i n t h e i r s t a t e of b a l a n c e q u i c k l y because
of t h e i r complex feedback systems. Under
h e a v i e r l o a d s on t h e o t h e r hand, d r a s t i c changes must be e x p e t t e d p a r t i c u l a r l y i f c e r t a i n
key s p e c i e s a r e v e r y s e n s i t i v e t o t h e r e s p e c t i v e a i r p o l l u t a n t . But even v e r y low
p o l l u t a n t c o n c e n t r a t i o n s can produce q u i t e
c o n s i d e r a b l e e f f e c t s i n p l a n t communities,
e s p e c i a l l y i f s y n e c o l o g i c a l amplitudes of t h e
n a t u r a l community s p e c i e s a r e f a r a p a r t . Add i t i o n a l s t r e s s through p o l l u t a n t s of lower
dosage can lead t o d r a s t i c r e d u c t i o n i n v i t a l i t y of p l a n t s a l r e a d y l i v i n g o u t s i d e t h e i r
e c o l o g i c optimum. The r e l a t i v e l y h i g h susc e p t i b i l i t y of spruce ( P i c e a a b i e s ) i n t h e
Erz mountains (Materna, 1972) and i n t h e b o r e a l
c o n i f e r o u s f o r e s t s i n F i n l a n d (Huttunen, 1979)
might w e l l b e caused by t h e i r u n s u i t a b l e habi t a t s . Keeping t h i s i n mind, i t seems problematic t o t r a n s f e r those dose-effect rel a t i o n s h i p s determined from "production ecosystems1'--in which t h e food p l a n t s g e n e r a l l y
encounter f a v o r a b l e c o n d i t i o n s - - t o n a t u r a l
ecosystems.
The r e l a t i o n s h i p s enumerated up t o t h i s p o i n t
show c l e a r l y why emissions induce d e g r a d a t i o n
i n p l a n t communities. On t h e o t h e r hand spontaneous a d a p t a t i o n t o a i r p o l l u t i o n s t r e s s
may be observed--adaptation which does n o t
e n s u r e t h e s u r v i v a l of t h e s p e c i e s through
s t u n t i n g , b u t r a t h e r seems t o have g e n e t i c
o r i g i n s . When Marchantia polymorpha (Briggs ,
1972) was exposed t o l e a d , and v a r i o u s g r a s s
s p e c i e s (Bradshaw, 1971, 1972, 1976) were a f f e c t e d by copper and z i n c , more t o l e r a n t popu l a t i o n s developed i n a s h o r t time through
d i r e c t e d s e l e c t i o n . B e l l and Clough (1973),
B e l l and Mudd (1976), and Horsman and Wellburn
(1977) mention s i m i l a r p r o c e s s e s w i t h Lolium
perenne and Rumex o b t u s i f o l i u s s u b j e c t e d t o
decades of SO2 loading. F i n a l l y , t h e r e s u l t s
of long-term fumigation of n a t i v e g r a s s l a n d
( P r e s t o n and B u l l e t t , 1978) a l s o p o i n t t o t h e
f a c t t h a t under a n y t h i n g l e s s than a c u t e conc e n t r a t i o n s spontaneous a d a p t a t i o n may occur
i n t h e c o u r s e of t h e formation of a new secondary e q u i l i b r i u m , which may a l s o i n t e r r u p t
p o s s i b l e long-term i n j u r y ( P r e s t o n , l979a).
Accordingly, t h e dose and i t s r a t e of change
should b e a d j u s t e d over t h e long-term such t h a t
p l a n t communities r e t a i n t h e i r c a p a b i l i t y - even by t h e e v o l u t i o n a r y method mentioned above--to f u l f i l l t h e i r f u n c t i o n i n n a t u r a l and
a g r a r i a n ecosystems t o t h e f u l l e s t (Guderian
and Kueppers, 1979).
The g e n e t i c a l l y f i x e d v a r i a t i o n i n popul a t i o n s which i s expressed i n t h e d e s c r i b e d
spontaneous a d a p t a t i o n , p r o v i d e s t h e b a s i s
f o r b r e e d i n g of p o l l u t a n t r e s i s t a n t p l a n t s
through s e l e c t i o n and r e p r o d u c t i o n of r e l a t i v e l y r e s i s t a n t i n d i v i d u a l s (Bialobok, 1979).
The r e s p o n s e s of i n d i v i d u a l s and homotypic
p o p u l a t i o n s t a k i n g i n t o account i n t e r s p e c i f i c
r e l a t i o n s discussed i n t h i s section, lead t o
t h e community s p e c i f i c r e s p o n s e s shown i n F i g .
1 which range from i n s i g n i f i c a n t changes t o
t h e t o t a l d e s t r u c t i o n of p l a n t communities.
CONCLUSIONS
Contamination of e x t e n s i v e a r e a s due t o
i n c r e a s i n g emissions and c o n t r o l s t r a t e g i e s
u s i n g t a l l s t a c k s f o r d i l u t i o n h a s made t h e
s t u d y of p l a n t communities and ecosystems
e s p e c i a l l y n e c e s s a r y . To a i d i n r e c o g n i t i o n
of p o s s i b l e r i s k s and i n making d e c i s i o n s r e garding c o n t r o l measures a t t h e s o u r c e and i n
t h e a f f e c t e d a r e a , t h e f o l l o w i n g p o i n t s must
be c l a r i f i e d :
1. Under which doses do changes occur
i n s t r u c t u r e and f u n c t i o n of p l a n t communities
of d i f f e r e n t complexity?
2. To what e x t e n t do p l a n t communities
show more s e n s i t i v e r e s p o n s e s than t h e i n d i v i d u a l s p e c i e s composing them?
3. What a r e t h e mechanisms of t h e s e
changes?
P o i n t s of impact f o r a i r p o l l u t a n t s
i n t h e ecosystem.
Location of p o l l u t a n t s i n t h e ecosystem ( a s s i m i l a t i o n , accumulation,
b r e a k down).
- Direct stimulatory o r injurious
e f f e c t s on t h e i n d i v i d u a l s p e c i e s of
t h e community.
Causes and mechanisms of changes i n
competition e q u i l i b r i u m .
Secondary succession w i t h p a r t i c u l a r
a t t e n t i o n t o a d a p t a t i o n and compensation.
4. How a r e r i s k s determined f o r p l a n t
communities?
- Development of experimental d e s i g n s
and i n t e n s i f i c a t i o n s of epidemiol o g i c a l studies f o r the determination
of e f f e c t s t o h i g h l y s t r u c t u r e d systems.
- Establishment of permanent s t u d y
a r e a s t o i n v e s t i g a t e succession.
Use of model p l a n t communities a s
indicators i n eco-toxicological t e s t s .
A n a l y s i s of t h e c o n d i t i o n of ecosystems b e f o r e and a f t e r s t a r t - u p of
a p o l l u t a n t source.
5. What measures a r e n e c e s s a r y f o r t h e
p r o t e c t i o n of v e g e t a t i o n ?
- Determination of dose-response r e l a t i o n s f o r p l a n t communities a s a
b a s i s f o r r i s k p r e d i c t i o n s and t h e
e s t a b l i s h m e n t of s t a n d a r d s f o r ecosystems.
C o l l e c t i o n of g e n e t i c r e s o u r c e s i n
n a t u r a l r e s e r v e s and i n gene banks.
P r o t e c t i o n of endangered p l a n t communities, especially i n existing
n a t u r a l r e s e r v e s , from e f f e c t s of'
a i r pollutants.
Development and maintenance of a i r
p o l l u t a n t c o n t r o l s t r a t e g i e s allowi n g p o l l u t a n t dose and i t s r a t e of
change be s o c o n t r o l l e d t h a t t h e
s t r u c t u r a l d i v e r s i t y , and t h e ecol o g i c and economic f u n c t i o n s of t h e
vegetation, a s w e l l a s i t s function
a s a gene pool, a r e f u l l y p r o t e c t e d .
-
-
-
-
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LITERATURE CITED
Anderson, F. K.
1966. A i r p o l l u t i o n damage t o v e g e t a t i o n
i n Georgetown Canyon, Idaho, M. S. Thesis
Univ. Utah, 102 p., c i t e d i n : Treshow,
M., 1968. Phytopathology 58: 1108-1113.
B e l l , J. N. B., and W. S. Clough.
1973. Depression of y i e l d i n r y e g r a s s
exposed t o s u l f u r d i o x i d e , Nature 241,
5384: 47-49.
B e l l , J. N. B . , a n d C. H. Mudd.
1976. Sulphur d i o x i d e r e s i s t a n c e i n p l a n t s .
A c a s e s t u d y of Lolium perenne, In:
E f f e c t s of a i r p o l l u t i o n on p l a n t s ,
T. A. Mansfield, ed. p. 87-104, S o c i e t y
f o r Experimental Biology Seminar S e r i e s
1, Cambridge U n i v e r s i t y P r e s s .
Bennett, J. H., and A. C. H i l l .
1975. I n t e r a c t i o n of a i r p o l l u t a n t s with
canopies of v e g e t a t i o n , I n : J. B. Mudd,
T. T. Kozlowski, eds. Responses of p l a n t s
t o a i r p o l l u t i o n , p. 273-306, Academic
P r e s s , New York.
Bennett, J. P., and V. C. Runeckles.
1977. E f f e c t of low l e v e l s of ozone on p l a n t
c o m p e t i t i o n , J. Appl. Ecol. 14, p. 877-880.
Bialobok, S.
1979. I d e n t i f i c a t i o n o f r e s i s t a n t o r
t o l e r a n t s t r a i n s and a r t i f i c i a l s e l e c t i o n o r production of such s t r a i n s i n
o r d e r t o p r o t e c t v e g e t a t i o n from a i r
p o l l u t i o n , Symposium on t h e e f f e c t s of
a i r - b o r n e p o l l u t i o n on v e g e t a t i o n ,
August 20-24, Warsaw (Poland).
Bonte, J., and P. Louguet.
1975. I n t e r r e l a t i o n s between sulphur d i o x i d e
p o l l u t i o n and stomata1 movement i n Pelargonium hortorum: E f f e c t s of r e l a t i v e
humidity and CO2 c o n c e n t r a t i o n s i n a i r ,
P h y s i o l o g i e Vegetale 13, p. 527.
Bormann, F. H., and G. E. Likens.
1979. P a t t e r n and P r o c e s s i n a F o r e s t e d
Ecosystem, S p r i n g e r , New York.
Borsdorf, W.
1960. B e i t r a g e z u r Fluorschadensdiagnos t i k , I. Fluorschaden-Weiserpflanzen
i n d e r W i l d f l o r a , Phytopath. 2. 38,
p. 309-315.
Bradshaw, A. D.
1971. P l a n t e v o l u t i o n i n extreme environments, In: E c o l o g i c a l g e n e t i c s and
e v o l u t i o n , R. Creed, ed., p. 20-50,
Oxford
.
Bradshaw, A. D.
1972. Some of t h e e v o l u t i o n a r y consequenc e s o f being a p l a n t , Evolut. B i o l . 5 ,
Bradshaw, A. D.
1976. P o l l u t i o n and e v o l u t i o n , I N : E f f e c t s
of a i r p o l l u t i o n on p l a n t s , T. A. Mansfield,
ed., p. 135-159, S o c i e t y f o r Experimental
Biooogy Seminar S e r i e s 1, Cambridge.
Braekke, F. H., (ed.).
1976. Impact of a c i d p r e c i p i t a t i o n on f o r e s t
and f r e s h w a t e r ecosystems in Norway, Res e a r c h r e p o r t No. 6, SNSF p r o j e c t of t h e
A g r i c u l t u r a l Research Council of Norway
Brandt, C. J. and R. W. Rhoades
1972. E f f e c t s of l i m e s t o n e d u s t accumulation
on composition of f o r e s t community, Environ.
P o l l . 3 , p. 217-225.
Brandt, C. J., and R. W. Rhoades
1973. E f f e c t s of l i m e s t o n e d u s t accumulation
on l a t e r a l growth o f f o r e s t trees. Environ.
P o l l . 4:207-213.
Bredemann , G.
1956. Biochemie and P h y s i o l o g i e des F l u o r s ,
Akademie-Verlag, Berlin.
Briggs, D.
1972. Population d i f f e r e n t i a t i o n in Marchant i s polymorpha L. in v a r i o u s l e a d p o l l u t i o n
l e v e l s . Nature (London). 238: 166-167.
Cowling, D. W. and D. R. Lockyer
1976. Growth of p e r e n n i a l r y e g r a s s (Lolium
perenne L.) exposed t o a low c o n c e n t r a t i o n
of s u l p h u r dioxide. J. Exp. Bot. 27:411.
Davis, D. D. and R. G. Wilhour
1976. S u s c e p t i b i l i t y of woody p l a n t s t o s u l f u r d i o x i d e and photochemical oxidants. A
l i t e r a t u r e review, C o r v a l l i s Environmental
Research Laboratory, U.S. Environmental
P r o t e c t i o n Agency, EPA-60013-76-102.
Dochinger, L. S., C. E. S e l i s c a r and F. W.
Bender.
1965. E t i o l o g y of c h l o r o t i c dward of e a s t e r n
w h i t e p i n e , Phytopath. 55:1055.
Dunikowski, S.
1977. R e l a t i o n s h i p between i n c r e a s e in a i r p o l l u t i o n t o x i c i t y and e l e v a t i o n above
ground, Cz. IX. Meteorological s t u d i e s , Wyd.
I n s t y t u t Badawczy, Lesnictwa.
Fox, F. M. and M. M Caldwell
1978. Competitive i n t e r a c t i o n in p l a n t popul a t i o n s e x p o s e d t o supplementary u l t r a v i o l e t
B-radiation, Oecologia 36 (2):173-190.
Gaumann, E.
1951. P f l a n z l i c h e I n f e k t i o n s l e h r e , Birkhauser
Verlag, Basel.
Garber, K.
1967. Luftverunreinigung und i h r e Wirkungen,
Gebr. B o m t r a g e r Verlag, B e r l i n .
Gordon, A. G. and E. Gorham
1963. E c o l o g i c a l a s p e c t s of a i r p o l l u t i o n from
an i r o n - s i n t e r i n g p l a n t a t Wawa, Ontario, Ca.
J. Bot. 41:1063.
Greszta, J., S. Braniewski, K. MarczynskaGalkowska, and A. Nosek
1979. The e f f e c t of d u s t s e m i t t e d by nonf e r r o u s metal smelters on t h e s o i l , s o i l
m i c r o f l o r a and s e l e c t e d tree s p e c i e s ,
Ekol. p o l . 27:397-426.
Grodzinska, K.
1978. Mosses a s b i o i n d i c a t o r s of heavy metal
p o l l u t i o n in P o l i s h n a t i o n a l p a r k s , Water,
A i r , S o i l P o l l . 9:83-97.
Grossmann, F.
1970. E i n f l u s s d e r Ernahrung d e r Pflanzen auf
den B e f a l l durch K m k h e i t s e r r e g e r und
Schadlinge, Landwirtsch.
Forsch. 18(25).
Guderian, R.
1967. Reaktionen von Pflanzengemeinschaf t e n
des F e l d f u t t e r b a u e s auf Schwefeldioxideinwirkungen, S c h r i f t e n r e i h e d e r L a n d e s a n s t a l t
f u r Immissions- und Bodennutzungsschutz
des Landes Nordrhein-Westfalen in Essen,
Hef t 4 :80-100.
Guderian, R.
1970. Untersuchungen uber q u a n t i t a t i v e
Beziehungen zwischen dem Schwefelgehalt von
Pflanzen und dem Schwefeldioxidgehalt d e r
Luf t , 2. Pflanzenkrankh. Pflanzenschutz 77 :
200-220, 289-308, 387-399.
Guderian, R.
1977.
A i r P o l l u t i o n , P h y t o t o x i c i t y of a c i d i c
g a s e s and i t s s i g n i f i c a n c e in a i r p o l l u t i o n
c o n t r o l , S p r i n g e r , New York.
Guderian, R.
1980. T e r r e s t r i a l v e g e t a t i o n ~ a i rp o l l u t a n t
I n t e r a c t i o n s : non-gaseous p o l l u t a n t s ,
I n t e r n a t i o n a l conference a i r p o l l u t a n t s
and t h e i r e f f e c t s on t h e t e r r e s t r i a l ecosystem, May 10-17, Banff, A l b e r t a , Canada.
Guderian, R. and H. Stratmann
1962. Freilandversuche z u r E n n i t t l u n g von
Schwefeldioxidwirkungen auf d i e Vegetation,
I. T e i l : Ubersicht z u r Versuchsmethodik und
Versuchsauswertung Forsch. B e r . d. Landes
Nordrhein-Westfalen N r . 1118, Westdeutscher
Verlag, Koln und Opladen.
Guderian, R. and H. Stratmann
1968. Freilandversuche z u r E n n i t t l u n g von
Schwefeldioxidwirkungen auf d i e Vegetation,
111. T e i l : Grenzwerte s c h a d l i c h e r SO?Immissionen f u r Obstund F o r s t k u l t u r e n Sowie
f u r l a n d w i r t s c h a f t l i c h e und g a r t n e r i s c h e
P f l a n z e n a r t e n , Forsch. Ber. d. Landes Nordrhein-Westfalen N r . 1920, Westdeutscher
Verlag, Koln und Opladen.
Guderian, R. and K. Kuppers
1979. Problems in determining dose-response
r e l a t i o n s h i p s a s a b a s i s f o r ambient pollut a n t s t a n d a r d s , Symposium on t h e e f f e c t s
of a i r - h o m e p o l l u t i o n on v e g e t a t i o n ,
August 20-24, Warsaw (Poland).
Hajduk, J.
1961. Q u a n t i t a t i v e und q u a l i t a t i v e Anderungen
d e r Phytozonosen v e r u r s a c h t durch Exhalationsprodukte von Fabriken, B i o l o g i a ,
B r a t i s l XVI,6:404-419.
H a l l , A. E. and M. R. Kaufmann
1975. Stomata1 response t o environment with
Sesamum indicum L., P l a n t P h y s i o l . 55:455.
Harvard, M. and M. Treshow
1975. Impact of ozone on t h e growth and reproduction of u n d e r s t o r y p l a n t s in t h e aspen
zone of western USA, Environ. Conserv. 2:
17-24.
Heagle, A. S. D. E. Body, and W. W. Heck
1973. An open top chamber t o a s s e s s t h e
Impact of a i r p o l l u t i o n on p l a n t s , J.
Environ. Qua1 2 (3) :365-368.
.
Heagle, A. S.
1979a. E f f e c t s of growth media, f e r t i l i z e r
r a t e and hour and season of exposure on
s e n s i t i v i t y of f o u r soybean c u l t i v a r s t o
ozone, Environ. P o l l . , l 8 ( 4 ) :313-322.
Heagle, A. S.
1979b. Ranking of soybean c u l t i v a r s f o r res i s t a n c e t o ozone u s i n g d i f f e r e n t ozone
doses and response measures, Environ P o l l .
19:l-10.
H i l l , A. C.
1971. Vegetation: A s i n k f o r atmospheric
p o l l u t a n t s . J. A i r P o l l . Contr. A s s . 21:
341-346.
Horsman, D. C . , and A. R. Wellburn
1977. E f f e c t of SO2 p o l l u t e d a i r upon enzyme
activity in plants originating fromareas
w i t h d i f f e r e n t annual mean atmospheric SO2
c o n c e n t r a t i o n s , Environ. P o l l . 1 3 ( 1 ) :33-40.
Huckabee, J. W.
1973. Mosses: S e n s i t i v e i n d i c a t o r s of a i r borne mercury p o l l u t i o n , Atmos. Environ. 7:
749-754.
Huttunen, S.
1979. The i n t e g r a t i v e e f f e c t s of a i r b o r n e
p o l l u t a n t s on b o r e a l f o r e s t ecosystems,
Symposium on t h e e f f e c t s of air-borne p o l l u t i o n on v e g e t a t i o n , August 20-24, Warsaw
(Poland).
Ionescu, A . , U. Sanda, E. Grou, and I. Buiculescu
1971. Considerations on t h e e f f e c t s of atmosp h e r i c i m p u r i f i c a t i o n upon t h e f l o r a and
v e g e t a t i o n of t h e Copsa Mica r e g i o n , Rev.
Rom. B i o l . Botanique 16: 125-139.
J a g e r , H. J. a n d H . K l e i n
1977. D i e Bedeutung stoffwechselphysiolog i s c h e r Reactionen von Pflanzen a l s
Kenngrossen f u r SO2-Immissions-wirkungen,
Phytopath. Z. 89(2) :128-134.
Jones, R. J. and T. A. Mansfield
1970. I n c r e a s e s in t h e d i f f u s i o n r e s i s t a n c e s
of l e a v e s in a carbon dioxide- enriched
atmosphere, J. Exp. Botany 21:951-958.
K a l e t a , M.
1972. D i e Wirkung von Magnesit-Immissionen
auf d i e Anderung von Pflanzengemeinscharten,
M i t t e i l u n g e n d. f o r s t l . Bund.vers.anst.
Wien 97(2) :569-584.
Karnosky, D. F. and C. R. S t a i r s
1974. The e f f e c t s of SO2 on in v i t r o f o r e s t
tree p o l l e n germination and tube e l o n g a t i o n ,
J. Environ. Qual. 3(4) :406-409.
Lee, J. J. and R. A. Lewis
1978. Zonal a i r p o l l u t i o n system: Design and
performance , I n : The bioenvironmental impact
of a c o a l - f i r e d power p l a n t , Third I n t e r i m
Report, C o l s t r i p , Montana, E. M. P r e s t o n and
R. A. Lewis, eds., EPA-60013-78-021, p. 322344, Oregon.
L e v i t t , J.
1972. Response of p l a n t s t o environmental
S t r e s s e s . Academic P r e s s , New York.
Linzon, S. N.
1978. E f f e c t s of a i r - b o r n e s u l f u r p o l l u t a n t s
on p l a n t s , I n : S u l f u r in t h e environment,
P a r t 11, E c o l o g i c a l impacts, J. 0. Nriagu,
ed. , p. 109-162, Wiley, New York.
Linzon, S. N . , R. G. Pearson, P. J. Temple and
W. D. McIlveen
1979. E f f e c t s on v e g e t a t i o n by power p l a n t
emissions of sulphur dioxide and s o o t , 72nd
Annual Meeting of APCA, June 24-29, Cincinn a t i , Ohio.
K e l l e r , Th.
1974. D i e Peroxidase--Aktivitat a l s Indik a t o r u n s i c h t b a r e r Immissionsschadigungen,
Anz. Schadlingskde. PflzSchutz, Umwelts c h u t z 47:86-89.
Lux, H.
1964. B e i t r a g z u r Kenntnis des E i n f l u s s e s d e r
I n d u s t r i e e x h a l a t i o n e n auf d i e Bodenvegetatrion
i n K i e f e m f o r s t e n (Dubener Heide) , Archiv f u r
Forstwesen 13: 1215-1223.
K e l l e r , Th.
1976. Zur P h y t o t o x i z i t a t von Fluorimmissionen
f u r Holzarten, M i t t . e i d g . Anst. F o r s t l .
Versuchswesen 5 1 (2) :301-331.
Mags ( M i n i s t e r f u r A r b e i t , Gesundheit und
S o z i a l e s des'Landes Nordrhein- Westfalen
1977. Umweltbelastung im Raum Dorsten, Analyse
und Problemosung, Dusseldorf.
Keller, Th.
1976. Wintertime atmospheric p o l l u t a n t s - do t h e y a f f e c t t h e performance of deciduous t r e e s in t h e ensuing growing season,
Environ. P o l l . 16:243-247.
Mandl, R. H . , L. H. Weinstein, D. C. McCune and
M. Keveny
1973. A c y l i n d r i c a l open-top chamber f o r t h e
exposure of p l a n t s t o a i r p o l l u t a n t s i n t h e
f i e l d , J. Environ. Qual. 2:371-376.
Kramer, F.
1976. ~ r s t eUntersuchungen z u r E r s t e l l u n g
eines Bundesbelastungskatasters (Pb, Zn,
Cd, Cu) in Raume Duisburg, Dinslaken,
S c h r i f t e n r e i h e d e r L a n d e s a n s t a l t f u r Immissions- und Bodennutzungsschutz des Landes
Nordrhein-Westfalen, Heft 39:45-48.
Materna, J.
1972. E i n f l u s n i e d r i g e r Schwefeldioxydkonzentrationen auf d i e F i c h t e , M i t t . f o r s t l .
Bund.Vers.Anst. Wien, 97 (I):219-232.
Laurence, J . A.
1978. E f f e c t s of a i r p o l l u t a n t s on p l a n t pathogen i n t e r a c t i o n s , 7 1 s t Ann. Meeting
of APCA, June, Houston.
Le Blanc, F. and D. N. Rao
1975. E f f e c t s of a i r p o l l u t a n t s on l i c h e n s
and bryophytes, I n : Responses of p l a n t s t o
a i r p o l l u t i o n , J. B. Mudd and T. T. Kozlowski, eds. , p 2 37-2 72, Academic P r e s s ,
New York.
.
Materna, J.
1979. E f f e c t s of p o l l u t i o n on t h e c a p a c i t y of
v e g e t a t i o n t o perform such f u n c t i o n s a s
water r e t e n t i o n , s o i l p r o t e c t i o n , w i l d l i f e
h a b i t a t , e t c . , Symposium on t h e e f f e c t s of
a i r - b o m e p o l l u t i o n on v e g e t a t i o n , August
20-24, Warsaw (Poland).
Materna, J., J. J i r g l e , and J. Kucera
1969. Vysledky mereni k o n c e n t r a c i k y s l i c n i k u
s i r i t i c e h o v l e s i c h Krusnych h o r , Ochrana
ovzdusi 6:84-92.
McClenahen, J. R.
1978. Community changes in a deciduous
f o r e s t exposed t o a i r p o l l u t i o n , Can. J. For.
Res. 8(4):432-438.
McCormick, R.
1963. Changes in herbaceous p l a n t community
during a t h r e e y e a r p e r i o d following exposu r e t o i o n i z i n g r a d i a t i o n g r a d i e n t s , 1st
Nat. Symp. Radioecol., Proc. Radioecology,
Reinhold Co., p. 271-275, New York.
P r e s t o n , E. M . , and T. L. G u l l e t (eds.)
1978. The bioenvironmental impact of a c o a l
f i r e d power p l a n t , Fourth I n t e r i m Report,
C o l s t r i p , Montana, U.S. EPA, C o r v a l l i s
Environmental Research Laboratory, C o r v a l l i s ,
Oregon.
McLean, D. C. and R. Schneider
1971. F l u o r i d e p h y t o t o x i c i t y :
Its a l t e r a t i o n by temperature, Proc. 2nd I n t e r n . Clean
A i r Congr., p. 292-295, New York.
Raabe, R. and K. H. Kreeb
1979. Enzyme a c t i v i t i e s and c h l o r o p h y l l and
p r o t e i n c o n t e n t i n p l a n t s a s i n d i c a t o r s of
a i r p o l l u t i o n , Environ. P o l l . 19:119-137.
Miller, P. R. and J. R. McBride
1975. E f f e c t s of a i r p o l l u t a n t s on f o r e s t s ,
In: Responses of p l a n t s t o a i r p o l l u t i o n ,
J. B. Mudd and T, T. Kozlowski, e d s . ,
p. 196-235, Academic P r e s s , New York.
Rentschler, I.
1973. Die Bedeutung d e r Wachsstruktur auf
den B l a t t e m f u r d i e Empfindlichkeit d e r
Pflanzen gegenuber Luf tverunreinigungen ,
Proc. 3 . I n t e r n . Clean A i r Congr., Dusseldorf,
p. A 139-A 142.
M i l l e r , J. E., D. C. Sprugel, R. N. Muller,
H. J. Smith and P. B. Xerikos
1979. An open-air fumigation system f o r
s t u d i e s of SO2 e f f e c t s on c r o p s , Environmental Research Contribution No. 79-21,
Argonne N a t i o n a l Laboratory, Argonne,
Illinois.
Mooi, J.
1974. Onderzoek n a a r de gevoeligheid en
opnamecapaciteit van h o u t i g e gewassen voor
HF , Groen 30 (10) :321-32 7.
Murphy, G. E., Jr., T. R. S i n c l a i r and K. R.
Knoerr
1977. An assessment of t h e use of f o r e s t s a s
s i n k s f o r t h e removal of atmospheric s u l phur d i o x i d e , J. Environ. Qual. 6:388-396.
N i k l f e l d , H.
1965. Beobachtungen i m Rauchschadensgebiet
eines Alumiumwerkes, Cbl. gas. Forstwesen
84 (2-6) :318-329.
Olsen, R. A.,
1976. Absorption of s u l p h u r d i o x i d e from t h e
atmosphere by c o t t o n p l a n t s , S o i l Science
84:107.
P i l e g a a r d , K.
1978. Airborne m e t a l s and SO2 monitored by
e p i p h y t i c l i c h e n s in an i n d u s t r i a l a r e a ,
Environ. P o l l u t . 17:81-92.
P o r t e r , L. K., F. G. V i e t s , Jr., and G. L.
Hutchinson
1972. A i r c o n t a i n i n g nitrogen-15 ammonia:
F o l i a r a b s o r p t i o n by corn s e e d l i n g s , Science
(N.Y.) 175: 759-761.
P r e s t o n , E. M.
1979. The e c o l o g i c a l i m p l i c a t i o n s of c h r o n i c
s u l f u r d i o x i d e exposure f o r n a t i v e grassl a n d s , 72nd annual meeting of t h e A i r Pollut i o n Control A s s o c i a t i o n , C i n c i n n a t i , Ohio,
June.
Rohmeder, E . , and A. von Schoenbom
1965. Der E i n f l u s s von Umwelt und Erbgut auf
d i e Widerstandsfahigkeit d e r Waldbaume
gegenuber Luftverunreinigungen durch Indust r i e a b g a s e - Ein B e i t r a g zur Zuchtung e i n e r
r e l a t i v rauchresistenten Fichtensorte,
Forstw. Cbl 84 :1-13.
Ruhling, A. and G. Tyler
1973. Heavy metal d e p o s i t i o n in Scandinavia,
Water, A i r and S o i l P o l l . 2:445-455.
Siccama, T. G. and W. H. Smith
1978. Lead accumulation in a n o r t h e r n hardwood f o r e s t , Environ. S c i . Tefchnol. 12:593-594.
Shinn, J. H., B. R. Clegg, and M. L. S t u a r t
1979. A minimum, f i e l d fumigation method f o r
exposing p l a n t s t o c o n t r o l l e d g r a d i e n t s of
a i r p o l l u t i o n l e v e l s , Contr. Environ. S c i .
Div., Lawrence Livermore Laboratory.
S h r i n e r , D. S.
1980. T e r r e s t r i a l v e g e t a t i o n - a i r p o l l u t a n t
i n t e r a c t i o n s : Non-gaseous p o l l u t a n t s , wet
d e p o s i t i o n , I n t . Conf. a i r p o l l u t a n t s and
t h e i r e f f e c t s on t h e t e r r e s t r i a l ecosystem,
May 10-17, Banff, A l b e r t a , Canada.
S i j , J. W.
1974. Short-term k i n e t i c s t u d i e s of t h e inh i b i t i o n of photosynthesis by s u l f u r d i o x i d e ,
J. Environ. Qual. 3:103.
Smith, W. H.
1974. A i r p o l l u t i o n e f f e c t s on t h e s t r u c t u r e
and f u n c t i o n of t h e temperate f o r e s t ecosystem, Environ. P o l l . 6:111-129.
S t o k l a s a , J.
1923. D i e Beschadigung d e r Vegetation durch
Rauchgase und Fabrikexhalationen B e r l i n .
Tamm, c. 0.
1976. Acid p r e c i p i t a t i o n : B i o l o g i c a l e f f e c t s
in s o i l and on f o r e s t v e g e t a t i o n , Ambio 5:
235-238.
Taoda, H.
1977. Bryophytes a s i n d i c a t o r s of a i r pollut i o n , In: Science f o r b e t t e r environment,
Y. Fukushima, ed., p. 292-301, Proc. I n t .
Congr. on t h e Human Environment, Kyoto 1975.
Taylor, 0. C.
1975. A i r P o l l u t i o n i n j u r y t o p l a n t p r o c e s s e s ,
Hort. S c i . 10:501.
Taylor, G. E., Jr.
1978. P l a n t and l e a f r e s i s t a n c e t o gaseous
a i r p o l l u t i o n stress, New Phytol 80(3) :
52 3-534.
.
Thomas, M. D.
1961. E f f e c t s of a i r p o l l u t i o n on p l a n t s ,
I n : A i r p o l l u t i o n , WHO, Geneva, Monog.
S e r i e s , Vol. XXXXVI, p. 233-278.
Trautmann, W . , A. Krause, and R. Wolff-Straub
1971. Veranderung d e r Bodenvegetation in
K i e f e m f o r s t e n a l s Folge i n d u s t r i e l l e r
Luftverunreinigungen i m Raum MannheimLudwigshafen, S c h r i f t e n r e i h e Vegetationskunde 5:193-207.
Treshow, M.
1968. The Impact of a i r p o l l u t a n t s on p l a n t
p o p u l a t i o n s , Phytopath. 58:1108-1113.
UBA (Umweltbundesamt d e r Bundesrepublik
Deutschland, B e r l i n ) .
1977. B e r i c h t e 4/77, L u f t q u a l i t a t s k r i t e r i e n
f u r Cadmium.
U l r i c h , B . , R. Mayer, P. K. Khanna, and J.
Prenzel ,
1978. A u s f i l t e r u n g von Schwefelverbindungen
a u s d e r L u f t durch e i n e n Buchenbestand, 2.
Pflanzenemahrung Bodenkunde 141:329-335.
Wentzel, K. F.
1962. Konkrete Schadwirkungen d e r Luftverunreinigung in d e r R u h r g e b i e t s l a n d s c h a f t ,
Natur Landschaft 37:118-124.
Wentzel, K. F.
1963. Waldbauliche Massnahmen gegen Immissionen, Allg. F o r s t z . 18:101-106.
Wentzel, K. F.
1965. D i e Winterfrost-Schaden 1962163 in
Koniferen- Kulturen des Ruhrgebietes, und
i h r e vermutlichen Ursachen, F o r s t a r c h .
36 :49-59.
Wentzel, K. F.
1968. Empfindlichkeit und Resistenzunters c h i e d e d e r Pflanzen gegenuber Luftverunr e i n i g u n g , F o r s t a r c h . 39 (9) :189-194.
Wentzel, K. F.
1979. D i e Schwefel- Immissionsbelastung d e r
Koniferenwalder des Raumes F r a n k f u r t Main,
F o r s t a r c h . 6:112-121.
Wentzel, K. F.
1980. Weisstanne
immissions e m p f i n d l i c h s t e
ein heimische Baumart, Allgemeine F o r s t
Z e i t s c h r . 14:373-374.
-
Wolak, Jr.
1971. S t u d i e s on t h e i n d u s t r i o k l i m a x i n
Poland, Methods f o r t h e i d e n t i f i c a t i o n and
e v a l u a t i o n of a i r p o l l u t a n t s I n j u r i o u s t o
f o r e s t s , Proc. XV IUFRO Congr., Wien.
Wolak, Jr. (ed.)
1977. R e l a t i o n s h i p between i n c r e a s e i n a i r
p o l l u t i o n t o x i c i t y and e l e v a t i o n above
ground, Wyd. I n s t y t u t Badawczy Lesnictwa,
Warsaw.
Wolak, J.
1979. Reaction des ecosystemes a l a pollut i o n subnecrotique, Symposium on t h e
e f f e c t s of air-borne p o l l u t i o n on vegetat i o n , August 20-24, Warsaw (Poland).
Woodwell, G. M.
1963. The e c o l o g i c a l e f f e c t s of r a d i a t i o n ,
S c i e n t i f . American 208 (6):40-49.
Woodwell, G. M.
1970. E f f e c t s of p o l l u t i o n on t h e s t r u c t u r e
and physiology of ecosystems, Science 168:
429-433.
ACKNOWLEDGMENT
Appreciation i s expressed t o Walter Jansen f o r
t r a n s l a t i n g t h i s manuscript from t h e o r i g i n a l
German.
Forecasting Effects of SO2 Pollution on
Growth and Succession in a Western
Conifer Forest
2
J.R. Kercher, M.C. Axelrod, and G.E. Bingham Abstract: A simulator has been developed for the mixed conifer forest type of the Sierra Nevada, California to forecast the effects of SO2 on forest growth and succession. The model simulates recruitment, growth, and death of each tree and is based on a northeastern USA simulator with extensive modifications. These modifications include the introduction of fire ecology, temporal seed crop patterns unique to the Sierra, and water stress. Pollutant stress is modeled as an effect on tree growth. The model simulates the shift from the ponderosa pine dominated forest type to the white fir dominated mixed conifer type as elevation increases from 5000 to 6000 ft. It also simulates the fire-suppression of white fir and the fire-climax of ponderosa pine. For a 10% growth reduction of ponderosa pine from pollutant stress and with growth reductions in other species as determined by their relative sensitivities, standing crops of ponderosa pine were reduced and white fir increased. It is anticipated that extensive fossil fuel energy development will occur in the United States over the next several decades with increased emis- sions of phytoactive effluents. It has long been recognized that many of these pollutants have de- leterious effects on the growth and behavior of vegetative communities. The effects of SO2 in particular have been extensively studied and occur at all levels of resolution from the metabolic pro- cess level to the ecosystem level. In the work reported on here, we wanted to predict the effects at the population and community levels given the results of the effects at the whole plant level. We have developed other models to forecast effects at the process level (Kercher 1977; Kercher 1978). The model, SILVA, uses an empirical dose-response relationship for the effects of pollutants at the tree-level. By virtue of the ecological interac- tions contained in the model, the effects at the tree level are translated into effects at the community level. We have followed the modeling approach devel- oped by Botkin and others (1972) who developed presented at the Symposium on Effects of Air Pollutants on Mediterranean and Temperate Forest Ecosystems, June 22-27, 1980, Riverside, California, U.S.A. ~nvironmentalScientist; Electrical Engineer; and Environmental Scientist, Lawrence Livermore Natl. Laboratory (LLNL), Livermore, Calif. opera- ted by the University of California for the Dept. of Energy under contract number W-7405. JABOWA, a simulator of forests of the northeastern USA. For a case study, SILVA has been applied to the ponderosa pine and mixed conifer forest types of the Sierra Nevada, California, USA. The asso- ciated species in these forests are ponderosa pine (Pinus ponderosa), white fir (Abies concolor), Douglas-fir (Pseudotsuga menziesii), sugar pine (Pinus lambertiana), incense-cedar (Libocedrus or Calocedrus decurrens), California black oak (Quercus kelloggii), and Jeffrey pine (Pinus Jeffrey!). MODEL DESCRIPTION SILVA calculates environmental parameters of the stand and initializes number and sizes of the trees from environmental and control data respec- tively. A table of good and bad seed crop years and a list of fire years is generated. The effect of pollution on trees is calculated. The number of new seedlings for that year, the growth of each tree,,and mortality are then determined for each year. Growth is modeled as a difference equation in the tree dbh and as a function of en- vironmental variables. The killing is done sto- chastically depending on the probability of death as determined by ecological risk, lack of growth, and fire damage. The dynamics of fuel accumulation (litter and brush) are also modeled. Temporal Seed Crop Patterns--For the conifers of the Sierra Nevada, there can be significant temporal variations in the annual cone production. We modeled the phenomenon of high and low yield seed years as .a Bernoulli random process with blocking. If the species is in an unblocked state, the probability of a good crop is p and of a poor crop is (1-p). If a good seed crop occurs, the the process is assumed to be blocked for r-1 years. The parameters p and r were taken from cone crop data. dels the probit of the effect being proportional to the log of the generalized dose. SIMULATION RESULTS Fire Ecology--Fire is a critical factor in the population dynamics of western forests. The most important aspect of fire is fire-induced mortality. The occurrence of fire was also modeled as a Bernoulli random process with blocking and p and r are based on fire incidence data. The blocking in this case arises from the time required for fuel to build back up to levels capable of sup- porting fire propagation. Fire kills by raising the temperature inside the tree and by damaging the crown. Fire intensity is calculated in kilo- watts/meter of fireline length using FIREMOD (Albini 1976) and probability of death is deter- mined as a function of dbh, bark thickness, and scorch height. Scorch height is calculated from fire intensity, ambient temperature, and windspeed. Moisture Stress--The effects of moisture stress are modeled by multiplying the difference equation for growth by a moisture stress factor. Parame-
ters for this function are taken from published ranges of tolerance data. The moisture stress factor is a function of the ratio of actual evapo- transpiration to potential evapotranspiration. MODELING SO2-POLLUTANT EFFECTS It has long been held that chronic injury re- sults from sulfate accumulation in plant tissues. Guderian (1977) has suggested that in most cases involving a single point source, chronic injury results from the "short-term action of relatively high concentration peaks". Thus the long-term average air concentration can be quite low due to the large number of pollution-free time periods. Because two different perspectives exist, i.e., (1) measuring average annual concentration or accumulated dose or (2) regarding injury as aris- ing from episodes and making detailed measurements of episode parameters, we have two different pol- lutant-effects submodels. Fire Ecology--Figure 1 shows the response of ponderosa pine and white fir with fire occurring at the natural frequency and with complete fire suppression. Ponderosa pine is well adapted to fire and dominates where undergrowth is thinned by fire. The model reproduces this result and indi- cates white fir would eventually outcompete pon- derosa pine in the absence of fire. The model suggests that a significant factor in the fire adaptation of ponderosa pine is its growth rate and growth form which allow it to evade fire by minimizing the time that the crown is exposed to fire. The effects of fire on tree mortality is shown in figure 2a. Note the shift in age of death to the lower ages in the presence of fire. Pollution Simulations--As an example of effects of pollution, consider the minimally significant case of 10% growth reduction in ponderosa pine. We scaled the response of the remaining species according to their published relative sensitivi- ties. These calculations used the seasonal aver-
age model. The results for ponderosa pine and- white fir (fig. 3) indicate that while white fir undergoes a nominal growth reduction of about 1 to 2% per tree with pollution, total basal area actu- ally shows a dramatic increase. This is due to the much greater growth retardation that the do- minant species experiences. Tree mortality of ponderosa pine (fig. 2b) indicates the trees are at higher risk at higher ages under pollution. The older, slower growing, pollution-stressed trees have size-dependent risks comparable to those of the younger unstressed trees. We can summarize (fig. 4 ) the results for ponderosa pine,
4
0
25
Seasonal Average Submodel--This approach as- sumes that growth reduction is a simple function of the SO2 concentration averaged over the growing season, or equivalently, of the integral of SO2 concentration over time. We use a dose-response function in which growth decreases linearly with increasing accumulated dose based on the prelimi- nary study of the tree-ring data of Lathe and McCallum (1939) for ponderosa pine grown near the smelter at Trail, B.C. ,
1
,
1
,
I
'
30 35
Without fire
- 10
-1
-
I
.c
E 5
So
L
14
~
l
l
l
l
t
l
~
Without fire
12
10
Successive Episode Model--An alternative ap- proach is to calculate the accumulated damage caused by successive short episodes separated by time intervals with no or negligible pollution. One method to implement this approach would be to use a process model (Kercher 1978). The method used here is an empirical dose-response where the dose is that accumulated from successive episodes (Kercher and Axelrod 1980). We use the empirical dose-response of Larson and Heck (1976) which mo- 4
With fire
^-,,
2
0
100
200
300
400
500
Time from clearcut (yr)
Figure I--Average of basal area from 25 simula- tions showing effects of fire. (a) Ponderosa pine (b) White fir. 0.080 EÑÑ
Ponderom Pine
Ponderom Pine
0.070
0.060
NO SO,
With SO,
-
0
Ponderosa Pine
Figure 2--Fraction of trees which died in simula- tions of figure 1 plotted against age at death. (a) With and without fire. (b) With and without pollution. -
l
1
0
100
'
l
r
l
White Fir
,
200
T
l
300
l
~
'
I
400
~
l
~
500
Time from clearcut lyr)
Figure 3--Basal area growth with and without pol- lution for (a) pine and (b) fir. white fir, and Douglas-fir by using boxplots of the distributions of the 500 annual data points of each species fraction of the total basal area. Note the decrease in pine and the increase in fir with pollution. The basal area of Douglas-fir is extremely reduced. The environmental conditions were poor for Douglas-fir even in the absence of SO?. The competitive disadvantage for Douglas-fir is made worse by pollution because Douglas-fir is sensitive to SO->and carries its needles longer than ponderosa pine. Thus the growth reduction for an individual tree (greater than that for pon- derosa pine) translates into a much larger effect on basal area. LITERATURE CITED Albini, F.A. 1976. Computer-based models of wildland fire behavior: a user's manual. 68 p. USDA For. Serv., Intermt. For. and Range Stn., Ogden, Utah. White Fir
Douglas Fir
Figure 4--Boxplots of polluted and unpolluted cases. Median is line at notches. Top of box is 75th percentile; bottom of box is 25th. Range is vertical line. Non-overlapping notches indicate significance at 95% level. Botkin, D.B., J.F. Janak, and J.R. Wallis. 1972. Some ecological consequences of a compu- ter model of forest growth. J. Ecol. 60: 849-872. Guderian R. 1977. Air pollution. 127 p. Springer-Verlag, New York. Kercher, J.R. 1977. GROW1: A crop growth model for assessing impacts of gaseous pollutants from geothermal technologies. UCRL-52247, 33 p. Lawrence Livermore Natl. Laboratory, Livennore, Calif. Kercher, J.R. ,
1978. A model of leaf photosynthesis and the effects of simple gaseous sulfur compounds (H2S and SO2). UCRL-52643, 37 p. Lawrence Livennore Natl. Laboratory, Livermore, Calif. Kercher, J.R. and M.C. Axelrod. 1980a. A model for forecasting the effects of SO2 pollution on succession in a western coniferous forest: Interim Report. UCID-
18537. 58 p. Lawrence Livennore Natl. Labora- tory, Livermore, Calif. Kercher, J.R. and M.C. Axelrod. 1980b. SILVA: a model for forecasting the effects of SO2 pollution on growth and suc- cession in a western coniferous forest: Final report. UCID (to be published). Law-
rence Livermore Natl. Laboratory, Livennore, Calif. Larson, R.I. and W.W. Heck. 1976. An air quality data analysis system for interrelating effects, standards, and needed source reductions: Part 3. Vegetation injury. J. Air Poll. Control Assoc. 26:325-333. Lathe, F.E. and A.W. McCallum 1939. The effect of sulphur dioxide on the dia- meter increment of conifers. 3 Effect of
sulphur dioxide on vegetation. National Re- search Council of Canada. p. 174-206. N.R.C. No. 815. Ottawa, Canada. Forest Models: Their Development and
Potential Applications for Air Pollution
Effects Research1
H. H. Shugart, S. B. McLaughlin, and D. C. west2
Abstract: As research tools for evaluating the effects of
chronic a i r pollution stress, forest simulation models
offer one means of i ntegrati ng forest growth and development data with generalized indices of pollution stress.
This approach permits consideration of both the competitive
interactions of trees in the forest stand and the influences of the stage of stand development on sensitivity of
component species. A review of forest growth models,
including tree, stand, and gap models, i s provided as a
means of evaluating re1 ati ve strengths, weaknesses, and
1imi t s of appl i cabi 1i t y of representati ve examples of each
type. Data from recent simulations with a gap model of
eastern deciduous forest responses to a i r pol 1uti on stress
are presented to emphasize the potential importance of
competition in modifying individual species' responses in a
forest stand. Recent developments in dendroecology are
discussed as a potential mechanism for model validation and
extended appl i cati on.
Atmospheric emissions from widespread indust r i a l and urban sources have now significantly
a1 tered the a i r qua1 i t y of extensive forested
regions of the world. Wolak (1971) described
the influence of industrial emissions on
forested areas of Poland as an abiotic paranatural ecological factor.
He viewed the
results of these emissions on forest succession
as the establishment of a new final sera1 stage
termed the industrio-climax.
Assessing the
impacts of these changes and those which may
ensue as we rely increasingly on fossil fuels in
'presented a t the Symposium on Effects of Air
Pollutants on Mediterranean and Temperate Forest
Ecosystems, June 22-27, 1980, Riverside, California, U.S.A.
Z~esearch
Staff
Members
of
the
Environmental Sciences Division, Oak Ridge
National
Laboratory,
Oak Ridge.
Research
supported by the National Science Foundation's
Ecosystem Stud i es Program under Interagency
Agreement No.
DEB77-25781 with the U.S.
Department of Energy under contract W-7405-eng-26
with Union Carbide Corporation. Publication No.
1545, Environmental Sciences Division, ORNL.
the future i s a challenge made comsiderably more
d i f f i c u l t by the complex nature of forest ecosystems. The perennial growth habit of forest
trees and the nature of their competitive interactions in a forest community make d i f f i c u l t the
evaluation of chronic exposures of forests t o
atmospheric pol 1utants. Treshow (1970) pointed
out that t e r r e s t r i a1 ecosystems are del i cately
balanced with a structure that may depend on a
few c r i t i c a l species. He indicated the response
of vegetation may be slow, b u t once natural
balances are sufficiently disrupted, subsequent.
alterations may occur much more rapidly because
of irreversible a1 t e r a t i ons of essenti a1 system
functions or species interactions.
Traditionally, studies of responses of forest
trees t o a i r pollution stress have focused primarily on species level responses, seedlings, a
few selected physiological processes, and general ly simp1 i s t i c exposure regimes. While valuable informati on has been gained on specific
pl ant-pol lutant interactions, we s t i 11 know very
1 i t t l e about the potenti a1 effects of pollutants
on forest communities. For instance, how are
individual species effects integrated over space
and time into responses of the forest community?
What are the probable limits of impacts on
forests based on our current knowledge
s e n s i t i v i t y of individual species responses?
of
ORNL DWG 80 H U B ESD
M I D 1960's
To address these questions necessitates that
we combi ne both autecologi cal and synecological
approaches. The former we can derive in large
part from dose-response data for individual
species. In the l a t t e r task, we can derive from
the experiences of two decades of experimentation with mathematical simulation of the growth
and development of forest communi t i es (Rei chl e
and others 1973, Munro 1974, Shugart and West
1980). The purpose of t h i s paper i s to review
the basic components of these models with a view
toward understanding their strengths and weaknesses and t h e i r potential u t i l i t y as tools for
studying comnunity-1 eve1 responses to a i r pol 1ution stress.
Computer Models of Forest Dynamics
In the mid-19601s, foresters and ecologists
independently
began
to
develop extremely
detailed computer models of forest growth and
development.
Foresters realized that certain
changes in f o r e s t practice (e.g., change in
trees due to genetic improvement, use of fert i l i z e r in f o r e s t s ) would render less useful the
stand yield tables that had been laboriously
developed over the prior several decades. Some
foresters began to develop models of forest
growth and yield that could be calibrated on the
extant, stand-table data s e t s and could also be
used to incorporate some of the changes in
forestry practice ( f i g . 1). A t the same time,
ecologists became dissatisfied with the s t a t i c
notion of forest typology and developed intens i ve investigations (e.g.,
the International
Biological Program) of the dynamic aspects of
ecosystems.
This increased interest in ecosystem dynamics led naturally t o the development
of f o r e s t models. By the mid-1970's (fig. I ) ,
three approaches evolved to modeling the longterm dynamics of f o r e s t s (table 1). We will
discuss the u t i l i t y of each of these approaches
in terms of i t s applicability to assessing the
consequences of a i r pollution effects over long
time scales. The approaches are:
(1) Forest models consider the forest as the
focal point of the simulation model. Fore s t r y yield tables constitute a highly datadependent subset of these f o r e s t model s.
( 2 ) Tree models take the individual t r e e as
the basic unit of a f o r e s t simulator. The
degree of complexity ranges from simp1e
tabu1 ati on of the probabi 1i t i es of an
individual t r e e of one kind being replaced by
an individual of another kind t o extremely
detailed models that include 3-dimensional
geometry of different species at different
sizes.
( 3 ) Gap models dynamically simulate particul a r attributes of each individual tree on a
prescribed spatial unit of relatively small
LATE 1960's
M I D - 1970's
1
TABLES
FORESTERS RECOGNIZE
THE POSSIBILITY OF CHANGE
I N TREE GENETICS AND FORESTRY
PRACTICE
MODELS
WORK
PROPOSED
1
ECOLOGISTS BECAME
INCREASINGLY AWARE OF ECOSYSTEM
FOREST DYNAMICS AND OF
USE OF COMPUTERS
MODELS
"I
**
42
LATE 1970 '1
COMMUNITY
CLASSIFICATION
MODELS
4
PUBLISHED
APPLICATION OF DEVELOPED MODELS TO
NEW PROBLEMS INCLUDING POLLUTION EFFECTS
Figure I--Recent historical origins of computer
models used for pollution effects assessment a t
the forest ecosystem level.
size. The spatial unit i s usually either a
gap in the forest canopy or a sample quadrat.
In general, the model type used i s based on
the problem considered, the data available, and
the desire to develop a flexible model. The
t r e e and forest model categories correspond t o
the t r e e and stand model categories used in a
recent review of forestry models (Munro 1974).
In the present review, gap models (which might
be considered a special case of three models)
are recognized as a category developed exclusively for use in studying ecological succession.
Forest Models
Yield tables used in forestry management are,
in f a c t , empirical models of expected responses
of an even-aged forest of (usually) a single
species. In t h i s context, a forest i s taken as
a larger spatial dimension than either single
t r e e or gap models considered explicitly.
Comparable succession models have been
developed using a variety of mathematical
approaches. Most of these models consider the
landscape to be composed of a number of mosaic
elements that chanae in response to success.iona1
processes. These changes may be viewed as probalistit5
(e.g., Wilkins 1977, Hool 1966) or
continuous (Shugart and others 1973), depending
on modeling assumptions relating to the actual
size of the landscape considered. Forest models
tend to be data-dependent concerning changing
rates of the mosaic elements assumed to comprise
the forests, and the actual mechanisms that
cause the changes in the forests do not appear
explicitly in the models. All of the forest
models listed (table 1) require l i t t l e computer
time and can be solved analytically in many
-a---
Table 1.
C l a s s i f i c a t i o n and c h a r a c t e r i z a t i o n o f f o r e s t s i m u l a t i o n models as t o o l s f o r e v a l u a t i n g s t r e s s e f f e c t s .
Model
Age-structure
categor
Forest
Even ( u s u a l l y )
1
Space
Nonspatial
1
Assessment p o t e n t i a1
Examples
Limitations
Most y i e l d t a b l e s i n use i n
f o r e s t r y today
Usual 1y c a l i b r a t e d on
long-term data s e t s on
many d i f f e r e n t s i t e s .
Slow t o develop.
Advantages
High degree o f
r e a l ism because o f
data input.
Familiar t o the
f o r e s t r y industry.
Mixed
Tree
Nonspati a1
Even
~ 0 0 11966
Olson and C h r i s t o f o l i n i 1966
Moser and H a l l 1969
Shugart and o t h e r s 1973
Johnson and Sharpe 1976
W i 1k i n s 1977
U s u a l l y r e q u i r e s data
o r i n s i g h t s t h a t are
c o l l e c t e d over a l o n g
t i m e period.
Newnham 1964
Lee 1967
M i t c h e l l 1969
L i n 1970
B e l l a 1971
Hatch 1971
Hegyi 1974
L i n 1974
Require extremely
d e t a i l e d growth data
and o t h e r d e t a i l e d
parameters.
C m e r c i a l forests only
are considered.
Provide a r e g i o n a l
inventory o f effects.
Mathematically
simple and c o u l d be
coupld w i t h economic models.
Tremendous d e t a i l .
Economic v a r i aoles
(e.g.,
board f e e t ,
products) simulated
directly.
Establishment may n o t
be considered.
Nonspati a1
S p a t i a1
Mixed
Nonspati a1
Gap
Mixed
Vertical
C l u t t e r 1963
C u r t i s 1967
Dress 1970
Goulding 1972
S u l l i v a n and C l u t t e r 1972
Burkhart and Strub 1974
Solomon 1974
C l u t t e r 1974
E l f v i n g 1974
Adlard 1974
Arney 1974
Ek and Monserud 1974
M i t c h e l l 1975
Leak 1970
Bosch 1971
Namkoong and Roberts 1974
F o r c i e r 1975
Suzuki and Umemura 1974
Horn 1976
Noble and S l a t y e r 1978
Waggoner and Stephens 1970
B o t k i n and o t h e r s 1972
Shugart and West 1977
M i e l k e and o t h e r s 1978
Tharp 1978
Shugart and Noble 1980
Shugart and others 1980
Doyle and o t h e r s 1980
cases. All of these models could be
assessing the consequences of some
pollution effect on a region's forests
that the primary problem of estimating
e s t stand response could be overcome.
used for
inferred
assuming
the for-
Spati a1 l y Explicit Tree Models
Two categories of models in table 1 (evenaged or mixed age) are used almost exclusively
in sophisticated
evaluations of
planting,
Require extremely
d e t a i l e d growth data.
Commercial f o r e s t s o n l y
are considered.
Establishment may n o t
be considered.
Economic v a r i a b l e s
(e. g., board f e e t )
simulated d i r e c t l y .
F a s t computationally;
c o u l d be i n t e r f a c e d
w i t h economic models.
Detailed data
requirement.
Tremendous d e t a i l .
Computationally slow.
Have been proposed
f o r use i n long-term
p o l l u t i o n assessment.
Lack o f d e t a i l i n
output.
Require c l e v e r va1 id a t i on procedures.
Spatial i n the v e r t i c a l
dimension only.
Require c l e v e r v a l id a t i o n procedures.
Models nave oeen
explored f o r t h e i r
t n e o r e t i c a l aspects.
Level o f a b s t r a c t i o n
i s b o t h an advantage
and disadvantage.
Have been used i n
1ong-term p o l 1u t i on
assessment.
Complex parameters
can be i n f e r r e d from
ecological principles.
spacing, and harvesting schemes in commercial
forests. These models produce information used
primarily by 1arge governmental or industri a1
land managers which i s as a consequence, normally communicated by direct means that do not
necessarily involve the s c i e n t i f i c l i t e r a t u r e
e . g . , internal reports). The models we l i s t e d
i n these categories (table 1) are probably only
a subsample of such models that are actually in
use.
These models function by incrementing indivi dual trees (usually tree diameter, crown
volume, and various form and shape parameters)
periodically and are usually solved in 1- t o
5-year time steps. To i l l u s t r a t e the degree of
detail used in such models, Mitchell's (1969)
model of white spruce (Picea glauca) uses
branch-pruning of trees that overlap to determine competition interaction.
The models explicitly consider the crowding
of trees and can be easily adapted to either
even- or mixed-age stands.
In f a c t , Hegyi's
(1974) even-aged model i s derived from Arney's
(1974) mixed-age model, and Mitchell Is (1969,
1975) models are derived in the converse manner. The models are designed for commercial
forestry operations and do not include phenomena
that ecologists would expect in a succession
simulator. They generally ignore establishment
of invading seedlings and often use functions
for geometry of trees that could only be
expected to hold in young, vigorously growing
trees.
The models sometimes use thinning or
harvest as a surrogate for mortality. Because
of the level of detail needed, these models
synthesize great amounts of autecological data
that are usually only available for commercial
species and are difficult to extend to mixedspecies forests. Nonetheless, the FOREST model
( E k and Monserud 1974) does simulate mixedspecies, mixed-age northern hardwood forest in
Wisconsin. This model i s also being considered
for use in a pollution effects assessment problem (fig. 1). There i s also a potential t o
apply the other models of the commercial species
that should be expl ored.
Even-aged, Nonspatial Tree Models
Even-aged, nonspati a1 models have been used
in commercial forestry also and are logical nonspatial a1 ternatives to models in the previous
category.
Nonspatial models have been used
almost exclusively in pine (Pinus spp.) plantations and are usually in the form of different i a l equations with basal area, stocking
density, and volume (biomass) of a forest stand
changing with respect to time. Because these
relationships are functions of the size of the
average tree, the models contain parameters
derived from the expected growth of trees. The
even- aged, mono-speci es character of the simulated forests allows the assumption that mathematical functions for the expected response of
an average or typical tree are sufficient to
express these re1 ati onships among volume, stocking, and basal area. These models work best if
the trees tend to be the same size, which helps
t o explain the use of these models in the more
genetically optimized, short-rotation, crop-like
Pi nus plantations.
The underlying assumptions
of these models 1imit their applications to
even-aged stands, and the development of mixedaged models using t h i s approach i s difficult.
Unlike the spati a1 mono-species models we discussed previously, these models can, in some
cases, be solved analytically and, in all cases,
require only a moderate amount of computer time.
Mixed-age, Nonspatial Tree Models
These models simulate ecological succession
in naturally regenerated forests. Their emphas i s i s on birth/death processes affecting individual trees, and the importance of tree growth
and form i s greatly deemphasized. They are not
particularly complex (i.e., birth and death of
trees might be treated as simple stochastic
processes; rep1 acement of trees as a first-order
Markov process), b u t frequently i t i s the stated
objective of the authors to attempt to capture
the salient aspects of succession with a minimal
model representation.
In this objective, the
models are actually explorations into the consequences of theories and assumptions on the
nature of ecological succession based on the
attributes of the species involved (Gleason
1926, Drury and Nesbit 1973).
The models can provide considerable insight
into patterns of ecosystem dynamics and can be
solved analytically without resorting to digital
computation.
An example of t h i s modeling
approach (Noble and Slatyer 1978) uses the vital
attributes of species t o determine the expected
patterns of community successions generated by
competition among the species. Vital attributes
considered are the modes that a species uses t o
persist at a s i t e , the modes for establishment,
the avail abi 1i t y of a method or persistence
(e.g., seeds, vegetative sprouts) at different
l i f e stages of the plants (propagule, juvenile,
mature, extinct), and longevity of individuals.
Using these species attributes, they construct
schematic diagrams of changes that can be compared with observational data from a given area.
Gap Models
Gap models simulate year-to-year changes in
diameters of each tree on a plot of known area.
These models do not account for the exact location of each tree b u t use tree diameters t o
determine tree height and then use simulated
leaf area profiles to devise competition relationships due to shading. These models are
spatial in the vertical b u t not the horizontal
dimension. This simp1 i f ication greatly reduces
the cost of running these models and also eliminates the consideration of complex spatial patterns of trees, should t h i s be important in a
given application. The vertical gap models are
probably best used in studies of successional
dynamics of natural forests considered over long
time spans. Gap models have a1 so been the f i r s t
detailed succession simulators applied to a i r
pollution effects research.
Current Model Applications
Most models built s t r i c t l y for forestry use
are usually intended as applications in a
restricted set of specified circumstances.
Given the great specificity of the models, they
s t i 11 simul ate cornnerci a1 ly important forest
types, and i t is unfortunate that they have yet
to be used in any pollution effects studies.
Several of the succession models presented in
table 1 have been used in evaluating environmental impacts on naturally occurring forests.
Botkin (1973, 1977) considered the effects of
CO2 enrichment on plant growth and subsequent
effects on forest dynamics. He found t h a t an
a r b i t r a r i l y assumed percentage change in rate of
photosynthate production at the individual plant
level in CO2-enriched atmospheres was not
manifested directly as a change in forest
growth. Other effects such as plant competition
and shading tended to 1ower the magnitude of the
system response.
McLaughl i n and others (1978)
and West and other (1980) performed model
experiments on chronic a i r pollution stress
expressed as a change in growth rates of
poll uti on-sensi t i ve trees. They noted that the
response of growth over the long term and in
natural forests might vary in direction as well
as in magnitude from what one might predict from
1aboratory or greenhouse studies. Kickert ( t h i s
symposium) and Kercher ( t h i s symposium) have
also used these gap models of western forests to
investigate 1ong-term pollutant effects. All of
these studies identify a common problem; namely,
in natural forests where trees vary in spacing,
size, and competitive responses, one cannot
extrapol ate directly from 1aboratory studies t o
f i e l d conditions. Forest succession models can
provide and have provided a necessary adjunct t o
1abor atory-based assessments of environmental
effects. We will provide a detailed example of
such an application in the following section.
Gap Model Application
As used in the following example, the model
(the FORET model, Shugart and West 1977) considers 33 forest tree species native to the
southern Appal achi an region and simul ates growth
of individual trees on a circular 1112-ha plot.
The growth of each tree on a plot i s incremented
yearly as a function of (1) total annual growing
degree days (5.6OC base), ( 2 ) the total leaf
area of t a l l e r trees on the plot, ( 3 ) total number of trees on the plot, and (4) the size of
the tree. A typical simulation i s illustrated
in figure 2.
The selection of a species for the plot and
subsequent i n i t i a t i o n and growth of the tree are
based on si lvicul tural characteristics of each
species. These characteristics include:
(1) s i t e requirements for germination,
( 2 ) pal atabi 1i t y of seedlings for browsers,
( 3 ) sprouting potential, (4) shade tolerance,
( 5 ) germi nati on and growth temperature requirements, ( 6 ) inherent growth potenti a1 ,
( 7 ) longevity, and (8) sensitivity to crowding
stress ( f i g . 2). The i n i t i a l trees established
on a plot with bare soil are those having shadeintolerant growth requirements and germination
a f f i n i t i e s for mineral soil. As the simulation
ORNL-OWG
BLACK OAK
50
(I)
YELLOW POPLAR ( I 1
v
WHITE OAK ( R l
BLACK CHERRY ( S )
p
OTHER SPECIES
100
7 8 -6488RAR
TOTAL BIOMASS
'Y
. '&
---
0
200
400
TIME (yr)
Figure 2--Species and stand dynamics of a forest
with and without continuous exposure t o a i r
(unaffected;
----pollution
stress
affected).
proceeds, trees that have the a b i l i t y t o
germinate in leaf l i t t e r and grow under shaded
conditions are selected by the model.
Leaf
l i t t e r is assumed to have accumulated to a level
commensurate with the total tree biomass for the
plot. The amount of shade cast by each tree i s
a function of leaf area of the tree and i s calcul ated allometrical ly from i t s diameter by
totaling the leaf area of all t a l l e r trees on
the plot. Under optimal conditions, tree growth
i s assumed to occur at a rate that will produce
an individual of maximum recorded size ( d b h ) f o r
that species during the period of maximum
recorded age and i s based on a curci linear function that grows a tree t o two-thirds i t s maximum
dbh at one-half i t s age. Modifications reducing
this optimal growth are imposed on each tree by
some additive combination of shading and crowding from other trees on the plot and the stochastic variation from optimum climate. Optimum
climate i s defined as the means of the minimum
and maximum growing degree-days within an individual species range.
Death i s a stochastic
process with the probabi 1i t y of dying inversely
related to the yearly growth increment. Total
stand density characteristics are calculated
Ingrowth occurs by germination of
from dbh.
seeds and sprouting, and simulation may be initiated either from a bare plot or an existing
stand of a predetermined composition and
structure.
Validation of the FORET model was accompl ished by simul ati ng a deciduous forest stand
with and without American chestnut as a viable
species (Shugart and West 1977). Simulations
with chestnut removed produced forests of simi1ar composition to the contemporary, postchestnut blight forest. With chestnut included,
the model produced a forest similar (Spearman
rank correlation - r = 0.83, see Siege1 1956) in
composition to the re1 ati vely undistrubed southern Appalachian forest which existed around 1890
to 1910.
All simulations were typically
repeated for a large number of plots ( 2loo),
and interpretations were based on average bi omass of individual species and the forest stand
determined from the mu1 t i p l e runs.
By utilizing t h i s
the results of the
competition and a i r
t h i s , the f 011owing
ing the response of
considered:
type model, we investigated
interaction of forest t r e e
pollution stress. In doing
re1 evant questions concernforests to a pollutant were
(1) What level of a i r pollution s t r e s s would
be required to significantly a1 t e r f o r e s t
growth and development?
( 2 ) How are s t r e s s effects integrated over
time?
( 3 ) How important i s competition i n moderating or enhancing induced stresses on individual species?
( 4 ) How are species responses integrated
into the response of f o r e s t systems?
Application of the model t o the study of the
effects of a i r pollution stress on growth and
development of eastern forests necessitated (1)
developing a r a t i onale f o r cl assifyi ng species
in terms of t h e i r relative s e n s i t i v i t y to t h i s
stress and ( 2 ) i ncorporati ng growth reductions
into the model which reflected species' sensit i v i t y ranking and a range of impacts which
might be expected under f i e l d conditions.
Addressing the f i r s t task assumes that species vary measurably in t h e i r growth responses
to chronic a i r pollution stress. Such a conclusion i s intuitively obvious from a wealth of
data from controlled laboratory and f i e l d
studies where obvious differences in s e n s i t i v i t y
of foliage t o visible injury from a i r pollution
have been demonstrated. Data on relative sensit i v i t y of f o r e s t trees to growth reduction from
chronic a i r pollution s t r e s s are limited, however. In t h i s application, we made the assumption that trees most sensitive to f o l i a r injury
would also be most sensitive to growth inhibition. We group the 32 species into 3 sensitivi t y classes
(resistant,
intermediate,
and
sensitive), based on their relative s e n s i t i v i t y
to visible injury. The sensitivity classification was based on 10 years of f i e l d survey data
of vegetation near a coal-fired e l e c t r i c plant
(McLaughlin and Lee 1974) and an extensive
sunmary of f i e l d and laboratory data on susc e p t i b i l i t y of woody plants to SO2 and photochemical oxidants reported by Davis and Wilhour
(1976).
This classification then formed a
framework f o r addressing the second task,
determining appropriate levels of growth reduction to introduce into the modeled forest. For
eastern forests, t h i s task must also rely on the
rather 1imi ted data currently available from the
1i terature. However, one advantage of mathematical models i s that a range of s t r e s s levels
may be simulated.
While not providing exact
quantitative answers, such an approach does
permit one to bracket the range of likely
responses based on the best available data.
In the FORET approach, both the influence of
varying stress levels and the stage of f o r e s t
maturity at which stress was initiated were
examined. Results of a typical simulation a r e
presented in figure 2.
Here, responses of
selected species are shown from a simulation in
which annual growth inhibitions of 20, 10, and 0
percent were imposed on seedlings in sensitive,
intermediate, and resistant sensitivity classes,
respectively. Increases in biomass of 4 major
species [yell ow popl ar (intermediate), white oak
( r e s i s t a n t ) , black oak (intermediate), and black
cherry (sensitive)] , the coll ecti ve "other" species category, and total stand biomass were compared with and without simulated a i r pollution
stress as the forest developed over time.
The results indicated that competition within
the forest stand may greatly modify responses
predicted from individual species' s e n s i t i v i t y
to stress.
Both enhanced growth suppression
(black oak and black cherry) and reduced suppressi on (ye11ow popl a r ) were demonstrated.
These responses were attributed to s h i f t s in the
competitive potenti a1 of these species induced
by differential stress applied within the f o r e s t
stand. An examination of total biomass of a l l
species indicated that suppression could be
greater than (as high as 20 percent) or less
than ( < 5 percent) that of the weighted average
suppression (7 percent) imposed in the simulation.
Another useful capability inherent in simulation approaches i s that variations in stand
age and, relatedly, stand composition may be
introduced f o r the time of s t r e s s initiation.
In the FORET t e s t , stage of stand development
was also identified as an important modifier as
Yellow poplar, a
shown in figures 3 and 4.
f ast-growing,
shade-intolerant species which
showed growth stimulation when the seedling
forest was stressed ( i n i t i a t i o n time - year O),
ORNL- DWG 7 8 - 4 9 6 0 8 R
ORNL-DWG 7 8 - M 0 9 R
LIRIODENDRON TULIPIFERA
if0
QUERCUS VELUTINA
1
40 % STRESS
BEGIN YEAR 0
BEGIN YEAR 50
......... BEGIN YEAR 400
-----
40 % STRESS
BEGIN YEAR 0
----- BEGIN YEAR 50
........ BEGIN YEAR 400
5
0
0
50
400
450
200
250
309
YEARS
350
400
450
500
0
50
400
150
200
250
YEARS
300
350
400
450
500
Figure 3--Response of ye1 1ow pop1 a r ( L i r i odendron t u l i p i f e r a ) t o a 10% reduction in growth.
Growth reducing s t r e s s i s applied a t year 0,
year 50 or year 400.
Figure 4--Response
of black oak (Quercus
velutina) t o a 10% reduction in growth. Growth
reducing s t r e s s i s applied a t year 0, year 50 or
year 400.
showed growth reduction in the more mature
f o r e s t ( i n i t i a t i on time - year 50) where other
species compete more favorably in the closing
f o r e s t canopy. Black oak, on the other hand,
when stressed in the seedling f o r e s t showed a
g r e a t l y enhanced growth reduction. When. s t r e s s
was i n i t i a t e d a t year 50, however, the response
was q r e a t l y delayed until other more r e s i s t a n t
speci-es suih as Ghite oak began t o dominate (see
f i g . 2).
demonstrated by Fox and Caldwell (1978) in
studies with UV-B radiation. In s i t u a t i o n s of
severe mutualistic competition, some species
showed improved growth under the UV-B treatment,
a response a t t r i b u t e d t o improved competitive
status.
Other examples of changes in p l a n t
competition under a i r pol 1ution s t r e s s were
reviewed by Guderian and Kuppers (1980) in t h e
preceding paper in t h i s session.
The e f f e c t s of d i f f e r e n t i a 1 levels of sens i t i v i t y on growth and competition of f o r e s t
t r e e s which we have shown in f i g u r e 2 are supported by the f i e l d responses of deciduous t r e e s
measured by Brandt and Rhodes (1972, 1973). In
t h e i r studies of the e f f e c t s of 25 years of
limestone dust deposition on a deciduous f o r e s t ,
composition,
with
they found changes i n
increased dominance of ye1 1ow pop1 a r , white oak,
and red oak a t t h e s i t e of heavy dust accumulat i o n . Reduced l a t e r a l growth ( 2 18 percent) of
s e n s i t i v e species such as red maple, chestnut
oak, and red oak was accompanied by a 76 percent
increase i n l a t e r a l growth of yellow poplar a t
t h e t e s t s i t e near t h e limestone quarry (Brandt
and Rhodes 1973). Evidence of the amplification
of e f f e c t s of a b i o t i c s t r e s s by both i n t e r - and
intra-specific
competition
has
also
been
Validation of Forest Community Response t o S t r e s s
While the v a l i d i t y of model r e s u l t s may be
r e a d i l y checked against actual growth and development patterns of "normal" f o r e s t s of a region,
evaluation of responses of disturbed f o r e s t s
becomes a much more d i f f i c u l t task. I t implies
developing a c a p a b i l i t y t o c l e a r l y distinguish
differences among measured values of parameters
of stand growth and composition and those which
would have occurred in t h e absence of pollutant
s t r e s s . Accomplishing t h i s necessitates e i t h e r
obtaining measurements on comparable stands over
a v a r i e t y of s t r e s s l e v e l s or documenting t h e
growth c h a r a c t e r i s t i c s of t h e stand in question
before the s t r e s s was i n i t i a t e d .
In e i t h e r
case, the investigator i s faced with measuring
pollutant e f f e c t s in the f a c e of the wide varie t y of b i o t i c and a b i o t i c variables control 1ing
growth
of
comnun i t i es.
individual
trees
and
forest
Historicallyy
documentation
of
forest
responses to rather high levels of gaseous pollutants primarily SO2 and HFy from smelting
processes was f aci 1itated by the typical occurrence of we11 -defined gradients of stress with
distance from the sowce.
Gordon and Gorham
(1963)Â for instance, were able to measure
i ncreased numbers of higher p1 ant species a1 ong
a 63-km gradient from the smelters at Sudburyy
Ontario. These changes followed a generalized
pattern of rep1 acement of more highly evolved
species of 1ater successional stages by the more
broadly adaptedy stress-tolerant genera1 i s t s
which Woodwell (1970) reported following pointsource radiation s t r e s s of a deciduous forest
comnun ity.
Present-day a i r pollution stress regimes can
generally be characterized as induced by gene r a l l y lower levels of pollutants contributed by
mu1 t i p l e sources. High-level point sources have
been largely replaced by area sources where
1ocal topography and meteor01ogy combine t o
concentrate
mu1 t i point
eff 1uents.
C1 assic
examples are the Los Angeles Basin in the West
and numerous industri a1 corri dors a1 ong river
valleys in the East. These areas provide good
possibilities for examining species and commun i t y responses to chronic and occasionally acute
stress regimes.
Commun it.y-1 eve1 effects
of
oxi dants
on
forests of the San Bernardino Mountains near Los
Angeles were described originally by Miller
(1973) and have formed a basis for a broadly
based study of a variety of ecosystem processes
at t h i s s i t e . Kickert and Gimnel (1980) used
these data in parameterizing a forest simulation
model to describe these changes. In the Easty
McCl enahen (1978) examined 7 deciduous forest
stands located along a gradient of chronic a i r
pollution stress on a 50-km portion of the
heavi 1y industri a1 ized Ohio River
Valley.
Species richness evennessy and Shannon divers i t y index were genera1 ly depressed for both
overstory and understory layers in the forest as
proximity to industrial a i r pollution sources
increased.
Stem density in the overstory
decreasedy while lower s t r a t a showed increased
abundance of species along t h i s same gradient.
Shifts in re1 a t i ve species' importance were a1 so
noted.
Studies of the l a t t e r type provide very valuable data for describing the types of changes
that may x c u r under moderate pollution s t r e s s y
b u t are limited in their u t i l i t y for predicting
rates of change over time or at varying stress
levels.
Information of t h i s type may be contained in the chronology of t r e e growth at that
and other s i t e s however. Recent developments
in tree-ring analysis provide a potentially
powerful tool for analyzing both the rate and
direction of within-community changes.
Dendroecology i s a discipline of dendrochrono1 ogyy the science of dating annual growth
rings of woody plants ( F r i t t s 1971). I t can be
considered a companion tool with dendroclimatology to examine changes in tree growth in
re1 ation to local and regional environment. The
basic conceptsy applications, and limitations of
dendroecol ogy have been discussed by Fri t t s
(1971). In generaly i t r e l i e s on multivariate
s t a t i s t i c a l analysis t o identify principal
variables influencing tree growth.
Resultant
equations are in themselves models of individual
tree growth over time. As a tool for studying
a i r pollution effects, dendroecology permits
separation of effects of tree age and local
cl imate from those induced by a i r pollution
(Nash and others 1975). Phillips and others
(1977ayb) have used t h i s approach to correlate
growth reductions in stands of lob1 011y and
white pine with production levels near an army
munitions plant.
More relevant to the challenges of providing reliable predictions of
species and community-level changes i s the
potential u t i l i t y of t h i s technique for detecting growth responses in our eastern regional
environment. Measurements of growth reductions
of white oak in apparent response to chronic
s t r e s s of t h i s type have been reported near
LaPorte, Indianay by Ashby and F r i t t s (1972).
In t h i s casey the decade during which anomalous
growth reductions occurred was associated with a
heavy incidence of smoke and haze in that region.
Documentation of pollutant histories in the
broader regional context represents a more
d i f f i c u l t task b u t one of great importance t o
efforts t o eventually develop a predictive
potential.
A greatly expanded network of a i r
quality trends; howevery data for the past 40
yearsy during which emissions i n the Eastern
United States increased sharply, are lacking.
One potentially useful tool for obtaining hist o r i e s of exposure t o genera1 a i r pollution
s t r e s s i s heavy metal analysis in the individual
rings (Lepp 1977). This approach has been used
in Sweden (Symeonides 1979) t o construct histories of heavy metal pollutiony a1 though Ti an
and Lepp (1975) caution that factors such as
radial transport and soil uptake must be f u l l y
understood to use t h i s technique accurately. In
the Swedish study, both lead and copper showed
l i t t l e lateral movement and were useful in constructing a decade-level history of metal pollution at the study s i t e .
Recent developments
coupling x-ray emission spectroscopy (Val kovic
and other 1979) with growth-ring analysis show
promise for using a variety of trace elements
for historical analyses.
As these techniques
are developed furthery they may provide useful
data for constructing historical indices of
regional-scale chronic stress.
The tools for validating or modifying f o r e s t
simulators as predictive tools appear t o be
either available now or close at hand. We feel
that dendroecol ogi ca1 approaches have tremendous
potential for unlocking a wide variety of
species/comunity/environment interactions which
will make t h i s task ultimately possible. Probably t h e g r e a t e s t value of t h e f o r e s t simulat o r s i s in predicting the consequences of s e t s
of I'most 1ogical I' assumptions regarding poll ution e f f e c t s on t r e e s . Other assumed relationships can be tested e a s i l y y and new information
may be added as i t i s developed (Kozlowski
1980). The mode1 i s merely a tool t o be used in
t h i s synthesis and refining process.
LITERATURE CITED
Adlard P. G.
19ia. Development of an empirical competition
model f o r individual t r e e s within a stand.
In Growth models f o r t r e e s and stand simulation. J. F r i e s y ed. p. 22-37. Res. Notes
30. Department of Forest Yield Researchy
Royal College of Forestryy Stockholm.
Arneyy J. D.
1974. An individual t r e e model f o r stand simul a t i o n i n Douglar-fir.
In Growth models f o r
t r e e s and stand s i m u l a t i z . J. F r i e s y ed.
p. 38-40. Res. Notes 30. Department of
Forest Yield Researchy Royal College of
Forestryy Stockholm.
AshbyÂW. C. and H. C. F r i t t s .
1972. Tree growth and climate near LaPortey
Indiana. Bull. Am. Meteorol. SOC.
53: 246-251.
Bell a  I . E.
1971. Simulation of growthy y i e l d and management of aspen. Ph.D. Thesisy University
of B r i t i s h Columbi a  Vancouver.
Boschy C. A.
1971. Redwoods: A population model.
Science 162: 345-349.
Botkiny D. B:
1973. Estimating t h e e f f e c t s of carbon
f e r t i l i z a t i o n on f o r e s t composition by
ecosystem simulation. Proc. 24th
Brookhaven Symposium i n Biology. In G. M.
Woodwell and E. V. Pecan. p. 384-a4.
CONF-720510. Nati ona1 Techni ca1 Information
Servicey Springfieldy Virginia.
Botkiny D. B.
1977. Foresty 1akesy and t h e anthropogenic
production of carbon dioxide. BioScience
27:325-331.
Botkiny D. B. J. F. Janak? and J. R. Wallis.
1972. Some ecological consequences of a
computer mode1 of f o r e s t growth. J. Ecol.
60:849-872.
Brandty C. J a y and R. W. Rhodes.
1972. Effects of 1imestone dust accumulation
on composition of a f o r e s t community.
Environ. Pollut. 3:217-225.
Brandty C. J. and R. W. Rhodes.
1973. Effects of 1imestone dust accumulation
on l a t e r a l growth of f o r e s t t r e e s . Environ.
Po1 l u t . 4: 207-213.
Burkhart, H. E. and M. R. Strub.
1974. A mode1 f o r the simulation of planted
l o b l o l l y pine stands. In Growth models f o r
t r e e s and stand s i m u l a t z n . J. Fries, ed.
p. 128-135. Res. Notes 30. Department of
Forest Yield Researchy Royal College of
Forestryy Stockholm.
C l u t t e r y J. L.
1963. Compatible growth and y i e l d models f o r
lob101 l y pine. For. Sci. 9:354-371.
C l u t t e r y J. L.
1974. A growth and y i e l d mode1 f o r Pinus
r a d i a t a in New Zealand. In Growth models
f o r t r e e s and stand s i m u l ~ i o n . J. F r i e s y
ed. p. 136-160. Res. Notes 30. Department
of Forest Yield Research, Royal College of
Forestryy Stockholm.
C u r t i s y R. 0.
1967. A method of estimation of gross y i e l d
of Douglas-fir. For. Sci. Monogr. 13:l-24.
Davis D. D. and R. G. Wilhour.
1976. S u s c e p t i b i l i t y of woody plants t o
s u l f u r dioxide and photochemical oxidants.
EPA-60013-76-102.
71 p. USEPAY Corvall i s y
Oregon.
Doyley T. W a y H. H. Shugarty and D. C. West.
1980. A model of Puerto Rican tropical
montane f o r e s t . M.S. Thesisy University of
Tennesseey Knoxvilley Tennessee.
Dressy P. E.
1970. A system f o r t h e s t o c h a s t i c simulation
of even-aged f o r e s t stands of pure species
composition. Ph.D. Thesisy Purdue
Uni versi t y y Laf a y e t t e y Indiana.
Druryy W. H e y and I . C. T. Nesbit.
1973. Succession. J . Arnold Arbor.
Univ. 54:331-368.
Harvard
Elfvingy B.
1974. A model f o r t h e description of t h e
s t r u c t u r e in unthinned stands of Scots
pine. In Growth models f o r t r e e s and stand
s i m u l a t x n . J. F r i e s y ed. p. 181-189.
Res. Notes 30. Department of Forest Yield
Researchy Royal Co11 ege of Forestryy
Stockholm.
, A. R a y and R. A. Monserud.
1974. FOREST: A computer model f o r
simulating the growth and reproduction of
mixed f o r e s t stands. Research Report
A2635. p. 1-14 + 3 appendices. College of
Agricultural and Life Sciencesy University
of Wisconsiny Madison.
E.P.A.
1977. National Air Q u a l i t y y Monitoring, and
Emissions Trends Report. 1977.
EPA-45012-78-052.
Environmental Protection
Agency. Research Triangle Parky North
Carolina. 22 p.
Forciery L. K.
1975. Reproductive s t r a t e g i e s and the
co-occurrence of c l imax t r e e species.
Science 189:808-809.
Foxy F. M., and M. M. Caldwell.
1978. Competitive interaction in p1 ant
D O D U ~a t i ons e x ~ o s e dt o sutmlementarv
.,
u l t r a v i o l e t - B radiation. 0eco1ogia"
36: 173-190.
Johnsony W. C., and D. M. Sharpe.
1976. An analysis of f o r e s t dynamics in t h e
Northern Georgia Piedmont. For. Sci.
22~307-322.
Kozlowskiy T. T.
1980. Impacts of a i r pollution on f o r e s t
ecosystems. BioScience 30:88-93.
Kickerty R. N., and B. Gimmel.
1980. Data based f o r e s t ecosystem simulation
implications of possible f u t u r e trends of
ozone a i r pollution in Southern California.
In P ~ O C USFS
. ~ Symposium on Effects of Air
Pollutants on Temperate Forest Ecosystems.
In press.
F r i t t s y H. C.
1971. Dendrocl imatol ogy and dendroecology.
Quat. Res. 1:419-449.
Leaky W. B.
1970. Successional change in northern
hardwoods predicted by b i r t h and death
simulation. Ecology 51:794-801.
GI eason, H. A.
1926. The i n d i v i d u a l i s t i c concept of the
plant association. Bull. Torrey Bot. Club
53: 7-26.
Leey Y.
1967. Stand models f o r lodgepole pine and
limits t o t h e i r application. For. Chron.
43: 387-388.
Gordony A. G S y and E. Gorham.
1963. Ecological aspects of a i r pollution
from an iron s i n t e r i n g plant a t Waway
Ontario. Can. J. Bot. 41: 1063-1078.
Lepp, N. W.
1975. The potential of tree-ring analysis f o r
monitoring heavy metal pollution patterns.
Environ. Poll u t . 9~49-61.
Goulding, C. J .
1972. Simulation techniques f o r a s t o c h a s t i c
model of the growth of Douglas-fir. Ph.D.
Thesis, University of B r i t i s h Columbiay
Vancouver.
Lin, J. Y.
1970. Growing space index and stand
simul ation of young western hem1 ock i n
Oregon. Ph.D. Thesisy Duke Universityy
Durhamy North Carolina.
Guderiany R a y and K. Kuppers.
1980. Responses of plant cornunities t o a i r
pollution. In Proc. USFA Symposium on
Effects of AT
Pollutants on Temperate
Forest Ecosystems. In press.
Liny J. Y.
1974. Stand growth simulation models f o r
Doug1 as-f i r and western hem1 ock in t h e
Northwestern United States. In Growth
models f o r t r e e s and stand s i z l a t i o n .
J. Fries, ed. p. 102-118. Res. Notes 30.
Department of Forest Yield Researchy Royal
College of Forestryy Stockholm.
Hatchy C. R .
1971. Simulation of an even-aged red pine
stand in northern Minnesota. Ph.D. Thesisy
University of Minnesota, St. Paul.
Hegyi, F.
1974. A simulation mode1 f o r managing
jack-pine stands. In Growth models f o r
t r e e s and stand simTation. J. Fries, ed.
p. 74-87. Res. Notes 30. Department of
Forest Yield Researchy Royal College of
Forestryy Stockho lm.
Hool, J . N .
1966. A dynamic programing - Markov chain
approach t o f o r e s t production control. For.
Sci Monogr. 12: 1-26.
.
Horny H. S.
1976. Succession. In Theoretical ecology:
Principles and appEcations. R. M. Mayy
ed. p. 187-204. Blackwell S c i e n t i f i c
Pub1 ishers, Oxford.
McClenaheny J. R.
1978. Community changes in a deciduous f o r e s t
exposed t o a i r pollution. Can. J. For. Res.
8:432-438.
McLaughlin, S. B. and N. T. Lee.
1974. Botanical studies in the v i c i n i t y of
the Widows Creek Steam Plant. Review of a i r
pollution e f f e c t s s t u d i e s y 1952-1972y and
r e s u l t s of 1973 surveys. TVA I-EB-74-1.
62 p. Tennessee Valley Authorityy
Chattanoogay Tennessee.
McLaughliny S. B a y D. C. West, H. H. Shugart,
and D. S. Shriner.
1978. Air pollution e f f e c t s on f o r e s t growth
and succession: Applications of a mathematical model. In ProceY71st Meeting of
the Air P o 1 l u t i o ~ C o n t r o 1Association.
H. B. H. Coopery J r e Yed. In press.
Mielkey D. L m YH. H. Shugarty and D. C. West.
1978. A stand model f o r upland f o r e s t s of
southern Arkansas. ORNLITM-6225. Oak Ridge
Nati ona1 Laboratoryy Oak Ri dge, Tenn.
M i l l e r y P. R.
1973. Oxi dant-induced cornunity change in a
mixed conifer f o r e s t . & Air pollution
damage t o vegetation. J. A. Naegele ed. p.
101-117. Adv. in Chem. Ser. 122. American
Chemical Societyy Washingtony D.C.
Mitchell K. J.
1969. Simulation of growth of even-aged
stands of white spruce. Yale Univ. Sch.
For. Bull. 75: 1-48.
Reichley D. E. R. V. O8Nei1l, and J. S. Olson.
1973. Modeling f o r e s t ecosystems. Report of
International Woodlands Workshop. U.S.
International Biological Program [ ~ u g u s t
14-16> 1972Â Oak Ridge National ~ a b o r a t o r y ] ~
339 p.
Shugarty H. H e y T. R. Crowy and J. M. Hett.
1973. Forest succession models: A r a t i o n a l e
and methodology f o r modeling f o r e s t
succession over large regions. For. Sci.
19: 203-212.
Mitchell y K. J.
1975. Dynamics and simulated y i e l d of
Dougl a s - f i r . For. Sci. Monogr. 17:l-39.
Mosery J . W. and 0. F. Hall.
1969. Deriving growth and y i e l d functions f o r
uneven-aged f o r e s t stands. For. Sci.
15: 183-188.
Munroy D. D.
1974. Forest growth models - a prognosis.
In Growth models f o r t r e e s and stand simulat i o n . J. F r i e s y ed. p. 7-21. Res. Notes
30. Department of Forest Yield Researchy
Royal Co11 ege of Forestryy Stockholm.
Namkoongy G S y and J. H. Roberts.
1974. Extinction p r o b a b i l i t i e s and the
changing age s t r u c t u r e of redwood f o r e s t s .
Am. Nat. 108: 355-368.
Nash, T. H e y H. C. F r i t t s y and M. A. Stokes.
1975. A technique f o r examining non-climatic
variation in widths of annual t r e e rings
with special reference t o a i r pollution.
Tree-Ring Bull. 35: 14-24.
Newnham, R. M.
1964. The development of a stand model f o r
Douglas-fir. Ph.D. Thesisy University of
B r i t i s h Columbi a y Vancouver.
Nobley I . R . Â and R. 0. Slatyer.
1978. The e f f e c t of disturbance on plant
succession. Proc. Ecol. SOC. Aust. 10.
press.
P h i l l i p s y S. O a Y J. M. Skellyy and
H. E. Burkhart.
1977b. Eastern white pine exhibits growth
retardation by f l u c t u a t i n g a i r p o l l u t a n t
1evels: Interaction of r a i n f a l l ,- aqe,
- - and
symptom expression. Phytopathol ogy
67 :721-725.
Shugarty H. H . Â and D. C. West.
1977. Development of an Appalachian deciduous
f o r e s t succession model and i t s application
t o assessment of t h e impact of the chestnut
blight. J. Environ. Manage. 5: 161-179.
Shugarty H. H e y A. T. Mortlocky M. S. Hopkins,
and I. P. Burgess.
1979. A computer simulation model of
ecological succession in Australian subtropical r a i n f o r e s t . ORNLITM-7029. Oak
Ridge National Laboratoryy Oak Ri dgey
Tennessee.
Shugart, H. H., and I . R. Noble.
1980. A computer mode1 of succession and f i r e
response of the high a l t i t u d e Eucalyptus
f o r e s t s of t h e Brindabella Rangey Australian
Capital Territory. Austr. J. Ecol. In
press.
Shugarty H. H e y and D. C. West.
1980. Forest succession models.
( i n press).
BioScience
Solomony D. S.
1974. Simulation of t h e development of
natural and si1vicultura1ly t r e a t e d stands
of even-aged northern hardwoods.
Growth
models f o r t r e e s and stand simulation.
J. F r i e s y ed. p. 327-352. Res. Notes 30.
Department of Forest Yield Researchy Royal
College of Forestryy Stockholm.
~
In
Olsony J. S m Yand G. Christofolini.
1966. Mode1 simulation of Oak Ridge vegetation
succession. p. 106-107 in ORNLITM-4007.
Oak Ri dge National Laboratoryy Oak Ridge,
Tennessee.
P h i l l i p s y S. O., J. M. Skellyy and
H. E. Burkhart.
1977a. Growth f l u c t a t i o n of l o b l o l l y pine due
t o pericdic a i r pollution levels: Interaction of r a i n f a l l and age. Phytopathology
67: 716-720.
Sullivany A.
and J. L. Clutter.
1972. A simultaneous growth and y i e l d mode1
f o r l o b l o l l y pine. For. Sci. 18:76-86.
Suzukiy T a Y and T. Umemura.
1974. Forest t r a n s i t i o n as a stochastic
process 11. In Growth models f o r t r e e s and
J. F r i e s y ed. p. 358-379.
stand simulat%.
.
Syneon i des , C
1979. Tree-ring analysis f o r tracing the
h i s t o r y of pollution: Application t o a
study in Northern Sweden. J. Environ. Qual.
8: 482-486.
Tian, T. K., and N. W. Lepp.
1977. Further studies on the development of
tree-ring analysis as a method f o r cons t r u c i n g heavy metal pollution h i s t o r i e s .
Proc., Univ. Mo. Annu. Conf. Trace
Substances. Environ. Health 11:440-447.
Treshow, M.
1970. The impact of a i r pollutants on plant
populations. Phytopathology 58: 1108-1113.
Tharp, M. L.
1978. Modeling major perturbations on a
f o r e s t ecosystem. M.S. Thesis, University
of Tennessee, Knoxville. 52 p.
Valkovic, V., D. Rendic, E. K. Biegert, and
E. Andrade.
1979. Trace element concentrations in t r e e
rings as indicators of environmental
pollution. Environ. I n t . 2:27-32.
Waggoner, P. E., and G. R. Stephens.
1970. Transition p r o b a b i l i t i e s f o r a
f o r e s t . Nature 225: 1160-1161.
Watt, K. E. F.
1966. The nature of systems analysis. &
I
Systems analysis in ecology. K. E. F. Watt,
ed. p. 1-14. Academic Press, New York.
West, D. C., S. B. McLaughlin, and H. H. Shugart.
1980. Simulated f o r e s t response t o chronic
a i r pollution s t r e s s . J. Environ. Qual.
9: 43-49.
Wilkins, C. W.
1977. A s t o c h a s t i c analysis of the e f f e c t of
f i r e on remote vegetation. Ph.D. Thesis,
University of Adelaide, South Australia.
Wolak, J.
1971. Studies on t h e industrio-climax in
Poland. Proc., IV Congress of IUFRO Methods f o r t h e i d e n t i f i c a t i o n and evaluation of a i r pollutants injurious t o f o r e s t s .
p. 233-244.
Woodwell, G. M.
1970. Effects of uollution on t h e s t r u c t u r e
and function of ecosystems. Science
168:429-433.