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Maintaining and Creating
;..
Old Growth Structural Features
?(<) 1; <;>)c:(<)o- 1:5
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6:"1v
in Previously Disturbed Stands Typical
O..x.: '?
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c: .
•
C. D. Oliver
C. Harrington
M. Bickford
R.Gara
W. Knapp
G. Lightner
L. Hicks
-6
<;>). 1:,
.,...£,. (<)6
(<)
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of the Eastern Washington Cascades
? 1,.
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•
C. D. Oliver is Professor of Silviculture, University of Washington College of
Forest Resources, AR-10, Seattle, WA 98195.
C. Harrington is Research Silviculturist, USPA Forest Service, Pacific North­
west Research Station, Olympia, WA 98502.
M. Bickford is Forest Silviculturist, USDA Forest Service, Wenatchee Nation­
al Forest, Wenatchee, WA 98801.
R. Gara is Professor of Entomology, University of Washington College of
Forest Resources, AR-10, Seattle, WA 98195.
W. Knapp is Silviculturist, A.G. Crook Company, Beaverton, OR 97006.
G. Lightner is Silviculture Specialist, USDA Forest Service, Region 6, Port­
land, OR 97208.
"
r:"
L. Hicks is Manager of Fish and Wildlife Resources, Plum Creek Timber
Company, 2300 F.I.C., 999 Third Avenue, Seattle, WA 98104.
This paper is based on a report from the Washington State Working Subgroup
of the Silviculture Subcommittee of the Spotted Owl Recovery Team, U.S. De­
partment of Interior Fish and Wildlife Service; December 9, 1991.
[Haworth co-indexing entry note]: "Maintaining and Creating Old GroWth Structural Features in
Previously Disturbed Stands Typical ofthe Eastern Washington Cascades."Oliver, C.D.et a!. Co-pub­
lished simultaneously inthe Journal of Sustainable Forestry (1he Haworth Press, Inc.) Vol. 2, No. 3/4,
1994, pp. 353-387; and: Assessing Forest Ecosystem Health in the Inland West (eds: R. Neil Sampson
and David L. Adams) The Haworth Press, Inc., 1994,pp. 353-387. Multiple copies ofthis article/ch
ter may be purchased from The Haworth Document Delivery Center [1-800-3-HAWORTH; 9:00a.m.·
5:00p .m. (EST)].
© 1994 by The Haworth Press, Inc. All rights reserved.
353
,._,,_:,
354 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
ABSTRACT. Changes in old growth structural features as well as
susceptibilities to disturbances were projected in stands typical of the
eastern Washington Cascades. Projected changes with and without
silvicultural operations were made. Doing no silvicultural activities
in these stands will not rapidly increase old growth structural fea­
tures and will allow the stands to become very susceptible to insects
and wind breakage, followed by fires. Specifically designed silvicul­
tural operations can maintain or rapidly increase old growth structur­
al features and reduce susceptibilities to most disturbances. Unless
some trees killed in the silvicultural operations are removed, the
treated stands will become very susceptible to fires. Removing some
of the thinned trees can also offset the costs of doing the operations.
A landscape approach of treating various stands with different silvi­
cultural regimes will probably best maintain a dynamic balance of
structural features, a reduced susceptibility to various disturbances,
and a steady flow of wood for manufacturing.
0 liver et al. risks of wind or snow breakage, fires, insects, and diseases. Removal and
utilization of some thinned timber may offset the costs of manipulating
stands to reduce these risks.
Objectives
This study addressed typical, multiple cohort (uneven-age) stands and
dense, single cohort stands in the eastern Cascade Range of Washington
state, U.S.A!, to determine the following:
•
•
•
INTRODUCTION
•
Uneven-age harvesting and fire exclusion in mixed-conifer stands have
been predominant practices for many decades at mid elevations (the Abies
grandis and Pseudotsuga menziesii zones of Franklin and Dyrness 1973)
in the eastern Washington Cascade Range (Oliver et al. 1993). The practic­
es have generally increased the habitat for some old-growth related spe­
cies, such as the spotted owL Past logging practices (primarily high-grad­
ing) have increased the occurrence of hollow, rotted trees and diseased
(mistletoe) limbs which the spotted owl favors for nesting. Stand-replac­
ing fires in the late 1800s and early 1900s, followed by fire exclusion,
have resulted in dense stands of a single cohort (age class) with trees of
small diameters.
An initial reaction to the decline of old growth-related species popula­
tions is to stop all forestry-related activities in large forested areas, in case
these activities reduce habitat. Stopping all activities carries consequences
in itself, including the possibility that the stands will grow susceptible to
destruction by winds and heavy snows, fires, insects, or a combination of
these.. Many eastern Washington forests consist of partially harvested,
multiple cohort (uneven-age) stands and dense single cohort stands which
grew after fires. It is unknown whether old growth structures can be
maintained or achieved rapidly in these forests if they are left alone.
Silvicultural operations such as thinning are sometimes used to increase
timber value; however, they may also change the structural features of
stands for the benefit of wildlife. Silvicultural operations may also reduce
355
•
•
Will avoiding future forestry activities maintain and enhance old
growth structural features in previously selectively harvested stands?
Will avoiding future forestry activities achieve old growth structural
features in dense, single cohort forests?
Can silvicultural treatments be done to increase old growth structural
features more rapidly than would occur through growth wifuout ma­
nipulations in these two stand types?
How susceptible will these stands be to destruction by insects, winds,
snow, and fire with and without silvicultural treatments designed to
achieve old growth structures?
W hat will be the costs of silvicultural treatments designed to achieve
old growth structures?
How can these susceptibilities and costs be minimized?
This study projected changes in certain structural features important for
old growth species both with and without silvicultural treatments in two
representative stand types of the eastern Washington Cascades. The PROG­
NOSIS computerized stand projection model along with information from
other sources not available with PROGNOSIS were used to project changes
in stand structures (East Cascades variant of Prognosis model of Stage
[1973]; this variant was authored by R.Johnson and G.Lightner). .
The first part of this study was concerned with creating and mamtaining
viable old growth structural features, not with obtaining revenue from the
forest; therefore, this analysis' first assumed that no wood would be ex­
tracted, even when silvicultural treatments killed trees and left them stand­
ing or felled them. The second part considered the susceptibilities to dis­
turbances with and without active silvicultural treatments when the killed
trees are left in the woods following the treatments. The third part consid­
ered the costs/returns and susceptibilities to disturbances when the mer­
chantable killed trees were left in the woods versus removed in commer­
cial operations.
Oliver et al.
356 ASSESSING FOREST EC.OSYSTEM HEALTH IN THE INLAND WEST
Stand Structural Features Used by "Old Growth" Species
Structural featuresof forests, and associated habitats and plant and
aillmal populati<;ms, constantly fl:uctuate with tree growth and natural and
human distlirbances (Oliver· and. Larson 1990; Hunter 1990; Sprugel
_1 91 ). Changing· forest structures after disturbances have been described
in several ways, but generally de 'elop through several structural stages­
. first, open areas ("stand initiation stage," Oliver 1981); then, very dense
stands of trees with small diameters ("stem exclusion stage"); followed
by somewhat more open stands with an understory ("understory reiniti­
ation stage"); and, barring disturbances, eventually "old growth" struc­
.. tures. Minor disturbances which kill only some trees can create park-like,
open stands soon after the disturbance, followed by stands with dense
understories, and then "old grow$'' structures (Johnson et al. 1993).
-·.These StruCtural stages are not obligatory or predetermined, but are a
natural resl1lt of interactions _among trees (Oliver and Larson 1990). Cer­
tain plant and animal species require specific features commonly found in
one or a few of these structures. Presently, endangered species such as the
spotted owl are.believed to require certain structural features found in old
growth stands, although other speCies in danger of becoming extinct re­
. quire.other-structural conditions-such as open areas which occur immedi­
. ately after a disturbance. Animal species which use each structure as
habitat have existed in a dynamic state, expanding and declining in num­
ber and moving from one place to anotheras the stand structure changed.
Various structural features of ' old growth" stands have been described
by Frankljn et al. (1986). Thomas (1979) and Hunter (1990) have de­
: scfib d structural features of old forests important to various animals. Some
, :structural features of stands important for species associated with old
growth forests are:
·-
•
<Ul
y
Areas of sev r Ic opy la ers and long crown lengtlis.
Some or all of- the forest. flooc covered with ground vegetation.
- Ground vegetation is 100sely de(med, but generally is below about
4.5 to 6 feet
,
·-_ ,, ;: :
., . Some areas of narrow_. tree spacings (high tree numbers) and other
areas of wide tree spacings (low tree numbers).
A high combination of tree diameters. and tree numbers (often ex­
pressed as basal area). . ,
• -A relatively high percentage of the.overall area covered by foliage.
Foliage coverage is often expressed as the proportion of canopy clo­
sure (percent of total area covered by foliage). Foliage coverage is ·
also somewhat related to basal area.
•
•
_
•
•
•
357
Large tree diameters for developing hollow trees for nests and prey
habitat and for forming future down logs, and tall tree heights for
providing more vertical space within the forest.
Snags (dead standing trees) and large, hollow, living trees (a.k.a.
"green snags"). A minimum snag size may be necessary for nesting
sites in some areas.
Down logs similarly provide habitat and food fungal substrata. Large
logs are again more beneficial than small logs.
METHODS
Representative Stands
Two representative stand conditions-one typical of eastern Washington
multiple cohort (uneven-age) stands and one typical of dense, single co­
hort (even-age) stands-were used to project changes in structures and
likelihood of destruction by different disturbance agents with and without
silvicultural treatments (Table 1).
Projecting Structural Features
Structural features were described and projected for the representative
stands of Table 1. No model presently projects the full range of structural
features; consequently, several models as well as estimates based on pro­
fessional experience (where no model existed) were combined (on a com­
puter spread sheet).
Projected changes in structural features were made for 60 years-from
1990 through 2050. To gain initial (1990) values of snags, down logs, and
crown depths, projections were begun in 1950.
The PROGNOSIS model (Stage 1973) was used to project tree height
and diameter distributions, mortality, and live crown ratios. Crown radii
were calculated using equations from Moeur (1985). Percent crown clo­
sure was calculated by summing the crown projection areas for each tree
based on its crown radius. Understory vegetation presence and height were
estimated to be inversely proportional to amount of overstory closure,
based on professional experience.
.
Numbers of hard and soft snags by diameter class were calculated from
data on mortality and thinned (harvested) trees in PROGNOSIS using the
Snag Recruitment Simulator (SRS, East-side version, Marcot 1990). All
thinned (harvested) trees were assumed to be killed (i.e., by girdling or
359
Oliver et al.
.s
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other means) and left standing to form snags. Down log numbers by size
classes were calculated from differences in snag recruitment and snag
number. Log lengths were· assumed to· be '30 percent of total tree heights
(at time of death). Because of the dry climate, logs were assi.imed not to
decay appreciably during the 60 years ofthis study Tlie projections illus­
trate trends and relative values of stiUcturalJ eatures more acci.rrately than
they show precise values.
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A stand's susceptibility td disturbances is related to specific structural
features and:to external conditions such as insect populations and weather
patterns. Measurable relationships between starid structuraHeafures and
likelihood of destruction by various igexits were developed based on these
known biological relationships between stand st:n.lctures and disturbances.
Susceptibilities to different disturbances were converted to a proportion,
with a "susceptibility threshold" of 100 percent indicatirig very high vulner­
ability of a stand to the disturoance agent.These relationships show trends
of stand susceptibility with changes· in certain structural·features rather
than predict precise values. Additional research should increase the accu­
racy of specific predictions, but the general trends would be expected to
·
:
remain as illustrated.
Wind or Snow Breakage-Tree susceptibility to wind or snow breakage
was calculated by its height/diameter ratio (Halle; Oldeman, and Tolnlin­
son 1978). Although not calibrated for eastein Washington species, a gener­
al rule is that trees are susceptible to breakage when the ratio of height to
lower stem diameter (measured at 4.5 feet) is over 100 (assumes that
height and diameter are expressed in same units). A value of·100 was
assumed to give a susceptibility threshold of 100 percent.
Susceptibility to Fire -Fuel loads were ca1culated for dead trees"from
weight of dry crowns and limbs (material below i5 inches dia:rrieter) by
species and diameter whenever trees died usmg values·from BroWn et al.
( 1977). Fuels were assumed to remain for 50 years on the drY sites of this
study. Thirty tons of fuel per acre was considered a siisceptibilit)'threshold
of 100 percent. This sttidy probably:iin:derestirriated fuel loads because it
did not consider dead limbs or foliage shed from living trees, and it did not
consider· dead materials on the ground from ·previous stands·or before
1950 (when calculations started iinhis 'analysis); When:itrees were re­
moved in silvicultural operationS, fuel loads were reduced because the flam­
mable materials were reduced, crushed to the ground, or otherwise miti­
gated.
Insect Susceptibility-In the study stands, major insect concerns are
··
'
-· ·· · · ·
·
358
· ·
'
Projecting usceptibility to Disturbance ,'
0
-
·
"
'
·
.
,
·
western spruce budworm (Choristoneura occidentalis Freeman) and moun­
tain pine beetle (Dendroctonus ponderosae Hopkins). Susceptibility to
attack by western spruce budworm is related to the amount of Douglas-fir
and grand fir in the stand, the stand density, and the presence of multiple
canopy strata with Douglas-fir (Dfrr) and/or grand frr (Gfir) in an upper
stratum and grand frr in the lower stratum. A susceptibility value was
developed from the conceptual relationship by Dr. Gara and Dr. Oliver as
follows:
l.S*
[
E
BAGF + DF
X
BAtotal stand
+
[30* (BArotal - 100)]
+
40 (if stand
has DF
100
and
)
GF
lower stratum)
- 6o
]
in upper stratum and GF in
BA=Basal area, DF=Douglis-frr, GF=grand fir
Susceptibility to attack by mountain pine beetle is believed to increase
with increasing total stand density, closer spacing of ponderosa pines, and
larger diameters of ponderosa pines. A susceptibility value was similarly
developed by Dr. Gara and Dr. Oliver from the conceptual relationship as
follows:
30*
(BAtotal
- 100)
0.6* (TPAPonderosa pine)
+
+
(
1.7* (DBHPonderosa pine)
BA
/
)
in Ft2 acre D BH in inches
BA=Basal area, TPA=Trees per acre, DBH=Diameter at breast height
Silvicultural Regimes
Two active silvicultural regimes were used for manipulating each stand
(Table 2). The choice of not managing each stand is considered a third
(No Activity) regime. Most regimes in this study were single cohort
(even-age) regimes involving thinning treatments, although one regime­
Multiple Canopy-was a multi-cohort (uneven-age) regime and involved
regeneration as well as selection cutting treatments. Specifically chosen
361
Oliver et al.
360 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
regimes likely to achieve old growth structural features were utilized.
Other, more creative, regimes may actually achieve old growth features
more effectively.
Each regime was projected until 2050 A.D., with trees killed and left in
the stand and again with merchantable trees removed using standard thin­
ning and harvesting treatments. When not removed, killed trees were left
standing and frrst became hard snags, - then soft snags, and fmally downed
.
-
The silvicultural treatments used are common; consequently, it is cer­
tain that they can be accomplished. On the other hand, their timing, se­
quence, aiJ.d the resultant changes in stand structures are not common to ­
present forest management.
,
Costs and Returns from Silvicultura(Treatments
-.
'
Costs per acre for each silvicultural regime are shown in Table 3. These
costs do not include treatrrients to reduce susceptibilities to disturbance
agents and to control fires once sduteci. Costs of killing' trees by girdling to
achieve the various structures are estirriated to be $1.00 to $3.00 per tree,
depending on tree size ·
.. '
Returns to the landowner: when' merchantable trees were removed are
estimated. These values vary greatly with numbers arid siies of logs re­
moved, regional log prices, and time. For this paper, a stumpage value
(return to the landowner) of $250.00 per thousand board feet is assumed
for trees over 12 inches (at 4.5 feet). A value of $25.00 per green ton
minus $825.00 per acre harvesting cost was assumed to be returned to the
landowner for trees less than 12 inches in diameter. Costs and return values
are for comparison purposes, and are not discounted to a single time.
· '
- -
_
· ·
;
_
. .
RESULTS
Changes in Stand StructuresWiikout Timber Removal_
·
Barring disturbances (discussed later), relatively few structural changes
will occur in either the multi-canopy stands or the dense, single-cohort
stands between 1990 and 2050 without silvicultural manipulations. Unless
altered by silvicultural treatments or destroyed by winds, snows, frres, or
insects, the multiple canopy stands: willcontiriue to have relatively deep
foliage, two canopy layers, trees close together,, and trees and snags of
large diameters (Figures 1 through 5). The two canopieswill become less
TABLE 2. R presentative silvicultural regi m es for manipula ing each stand (Table 1) in this study. Detailed description of regimes can be found in Oliver et al. (1991)
·
··
.
MULTIPLECANOPY STANDS:
DENSE, SINGLECOHORT STANDS:
No Activities Silvicultural Regime:
No Management Activities are done in
stand. .•. ·.. .. •••. :
Low Density Regime:
Living trees in both strata are kept in a wide spacing by periedically killing many trees in both strata, beginning in 1992.. A third, forest floor. stratum is allowed to develop· naturally.
.
No Activities Silvicultural Regime:
·
·
·
·
·
·
·
.
Specific Activities: .
1992: Thin 70% of Douglas-fir and 50% of
grand fir..
.
2021: Thin all Douglas-firs and 80% of
grand fir (primarily regeneration).
.
No Management Activities are done in
stand.
.
.
MultipleCanopy Strata Regime: ,
All but a few overstory trees (6 trees/acre)
. ·are killed in ,1992; and trees of many
. species are allowed to develop naturally
in the uncjerstory. Second cohort
(age class) is allowed to develop rapidly by .
later killing some (but not all) of the oldest
.trees. Second cohort is kept at a wide spacing
by killing some trees. A forest floor stratum is
allowed to develop naturally.
·
· ·
·
.
.
·
.·..
Specific Activities:
1992: Thin all Douglas-firs and grand firs
and 85% of ponderosa pines.
2011: Thin 95% of Douglas-firs and all
High Density Regime:
Living overstory trees in both strata are
kept at a narrow spacing (but not as
narrow as the No Activities Regime
by periodically killing some trees
beginning in 1992. A third, forest floor
stratum is allowed to develop naturally.
Specific Activities:
1992: Thin 40% of ponderosa pines.
2021: Thin 85% of Douglas-firs and 55%
of grand firs (both regeneration and
older trees).
grand fir (both regeneration and older
trees).
2041: Thin 50% of Douglas-firs and all
grand fir (both regeneration and older
trees).
High Density Regime:
Living overstory trees are kept at a
narrow spacing (but not as n rr?w as , .
No Activities Regime) by penod1cally killing
some trees beginning in 1992. Understory
is allowed to develop naturally.
Specific Activities:
1992: Thin 50% of Douglas-firs and 30% of
grand firs
2011: Thin 70% of Douglas-firs and 90% of
grand firs (both regeneration and older
trees).
2041: Thin 95% of Douglas-firs, 90% of
grand firs (both regeneration and older
trees), and 5% of ponderosa pines.
· ·-:r
365
Oliver et a!.
CD(/)Ul'
Ez a; .!:2
"O
O:
::J
FIGURE 1. 60-year, stand silhouette projections showing structural features
typical of multiple canopy stands in eastern Washington under different
silvicultural regimes. (Scale on left (in feet) represents both horizontal and
vertical. Black crown Douglas-fir; white crown grand fir; spotted crown
ponderosa pine.)
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,...._ _ co_
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Y7 Y7 Y7
NO ACTIVITIES
lOOt·
,: w
1990
-
2010
2030
2050
150
W­
0: ro
>
0
<( 0
100
OOC\l
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Y7 Y7 Y7
(1)0:
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LOW D ENSITY
OC\ll!)
C\1 .­
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Y7 Y7 Y7
1990
at
2010
2030
2050
150
100
Cll
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Z..JIOZ
I
'::
HIGH D ENSITY
1990
2010
.
2030
2050
distinct after about 40 years (Figure 1). Large snags and down logs will
begin appearing in two to four decades (Figure 2). There will continue to
be little understory, however (Figure 1 ).
Dense, single cohort stands not altered by silvicultural treatments or
destroyed by disturbances will continue to have similar features for the
next 60 years (Figures 6-9). They will have a closed canopy of closely
',
•
'
•• , , '
:
r
•
,'
•
FIGURE 2. Projections of species diameters, and percent crown closure,
hard snag numbers, and down log _lengths for multiple canopy stands
(Figure 1). (Diameters show largest tree of each species and stand. Snags
and logs are in 3 diameter classes. N = No Activity Regime; L = Low Density
Regime; H =High Density Regime. Snag & down log scales are logarithmic.)
50
en
-
UJ
X
0
X
m
c
a:
·a:
u:
c
z
<
a:
(!:J
u..
1z
w
0
a:
w
a.
2000
2010
2020
2030
DATE (YEAR, A.D.)
2040
:2050
<
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0
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50
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20
2030
2020
DATE (YEAR, A.D.)
2010
2040
.
2030
2020
2010
DATE (YEAR, A.D.)
2000
1990
-- LOW DENSITY SYSTEM
NO ACTIVITIES
1000
100
!
L
LH
10
1990
CJ
2050
a:
0
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2040
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1990
.en
1
120
HIGH DENSITY SYSTEM
0
w
X
0
· m
c
0
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20
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140
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367
Oliver et al.
366 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
N
L
H
II
2000
N
N
L
H
L
H L
N
N
H
LH
N
H
I
2010 .
2020
2030
I
20 0
2050
DATE (YEAR, A.D.)
OVER 19" OBH
UNDER 11 INCHES DBH
M
11 to 19 INCHES DBH
H
10000
'
50
1w
w
40
X
1(!)
z
w
..J
30
(!)
0
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20
z
1000
100
10
1990
0
0
1990
-
2000
2010
NO ACTIVITIES
.
•.
2020
2030
DATE (YEAR, A.D.)
-+-
LOW DENSITY
2040
--«--HIGH DENSITY
2050
2000
2010
2020
2030
20 0
DATE (YEAR, A.D.)
3:
0
10
CJ
OVER 19" DBH
UNDER 11 INCHES DBH
ta
11 to 19 INCHES DBH
2050
FIGURE 3. Projections o f susceptibility o f multiple canopy stands following
different silvicultural regimes to destruction by common wind/snow and
insect disturbance agents. Susceptibility o f 100 = extreme likelihood of
disturbance. Susceptibility values over 200 were assigned a value of 200.
Wind and snow susceptibility listed by species. [] = No Activities Regime;
+ = High Density Regime; * = Low Density Regime.
200
PONDEROSA PINE WIND/SNOW
150
100
50
0
1990
2000
2010
2020
2030
2040
2050
w
()
z
<(
OJ
a:
::::>
1en
c
0
1>1:J
OJ
200
en
::::>
(/l
!-
5
J
2oo
....
2000
;s
2010
2020
2030
2040
2050
GRAND FIR WIND/SNOW
f-.
150
100
f
50
oL_
1990
WESTERN SPRUCE BUDWORM
150
w
()
z
<(
OJ
a:
::::>
1(/l
0
0
1>1:::i
OJ
i=
a.
w
()
en
::::>
(/l
5
OL--1990
200
�!
2000
2010
!
j,-s
2020
2030
DATE (YEAR, A.D.)
; ):(
2040
J
I
2050
-------------------------------2040
2030,
2020
2010
2000
2050
MOUNTAIN PINE BEETLE
150
10
J
:r
1990
100
1990
200
5
150
i=
a.
w
()
DOUGLAS-FIR WIND/SNOW
369
Oliver et al.
368 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
2000
2010
2020
2030
2040
2050
DATE (YEAR, A.D.)
spaced, small trees and some small snags and down logs (Figure 7). There
will continue to be only one canopy layer and a shallow foliage layer with
no ground vegetation (Figure 6).
The active silvicultural manipulations will dramatically change the old
growth structural features in both the multiple canopy and dense, single
cohort stands. Some old growth features will immediately increase, while
others will initially decrease and later increase. Changes in the various
structural features will be as follows:
.
Canopy Layers-The number of canopy layers will increase with the Mul­
tiple Strata regime in the dense, single cohort stands (Figures 6 and 9);
however, the active regimes may reduce the distinctiveriess of different canopy
layers in stands already containing muitiple canopy strata (Figure 1).
Foliage Depth-Foliage·depth will increase in all regimes as the number
·
'
·
of living trees is reduced (Figures 1 and 6).
Crown Closure-Reducing the mirriber of living trees through silvicul­
tural treatments will temporarily decreaSe crown closure (Figures 2 and
·
370 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
FIGURE 4. Projections of susceptibility of multiple canopy stands (top) and
dense, single cohort stands (bottom) to fires with no silvicultural activities ([])
and with various regimes where the thinned trees are left as snags or logs
are similar to effects of insects or wind/snow in leaving stands very suscepti­
ble to fires. Susceptibility values are similar to Figure 3. + = High Density
Regime;* = Low Density Regime (top) or Multiple Strata Regime (bottom);
Black boxes = Thinning regimes where killed trees are removed.
c
0
1990
2000
2010
2020
2030
2040
2050
DATE (YEAR, A.D.)
1>1::i
m
i=
ll..
w
()
(f)
::l
(f)
371
Tree Spacing-Tree spacing (Figures 1 and 6) will generally increase
with time and with lower density silvicultural regimes, except where the
Multiple Canopy regime allows abundant regeneration to develop.
Tree Size-Tree sizes will also increase with time, but will increase more
rapidly with lower density silvicultural regimes (Figures 2 and 7).
Snags and Down Logs-There will be many snags and down logs (Fig­
ures 2 and 7); however, down logs will be very small even under low
density silvicultural regimes during thefrrst few decades-until the snags
fall over. Active felling of dead trees could create large down logs more
rapidly. The down logs will last many decades.
Changes in Susceptibilities to Disturbances
Without Tree Removal
w
()
z
<1:
m
a:
::l
1(f)
0 liver et al.
100
50
0
1990
2000
2010
2020
2030
2040
2050
DATE (YEAR, A.D.)
:
7)-most dr�atically when dens , sirlgle, cohort stands are converted to
multiple canopy stands. Percent canopy closure will increase to very high
levels where light thinning treatments. (high density regime) left vigorous
trees in several canopy strata (Figure 2).
GroundYegetation-Few silvicultural regimes will maintain understory
- rrs to a
.vegetation because the shade tolerant grandfrrs (and Douglasf
lesser extent) will regenerate abundantly whenever there is a thinning or
similar disturbance (Figures 1 and 6).
Without silvicultural operations, the stands will become increasingly
susceptible to all disturbances (Figures 3, 4, and 8). Douglas-firs and grand
firs in the dense single cohort stands are already susceptible to wind/snow
breakage, and this susceptibility will increase. Both stand types will be­
come increasingly susceptible to the western spruce budworm and the
mountain pine beetle. Even without wind or insect disturbances adding to
the dead trees, both stand types will become increasingly susceptible to
fires (Figure 4).
The different silvicultural regimes will have varied effects on the multi­
ple canopy stands' susceptibilities to wind/snow and insect disturbances
(Figure 3). The stands are generally not susceptible to wind and snow
breakage, and the silvicultural regimes will not dramatically increase their
susceptibility. The light thinning regime will reduce the stand's suscepti­
bility to mountain pine beetle but will eventually increase the stand's
susceptibility to western spruce budworm. The heavy thinning regime will
reduce the stand's susceptibility to both the budworm and the beetle.
The dense, single cohort stands will become less susceptible to wind/
snow and insect disturbance agents following all active silvicultural re­
gimes (Figure 8). Thinning the dense, single cohort stands will make the
Douglas-firs much less likely to be destroyed by winds or snow or the
whole stand much less likely to be destroyed by the mountain pine beetle.
If Douglas-firs or grandfrrs had been left in the overstory in the "Multiple
Strata" regime (instead of ponderosa pines), the stand's susceptibility to
western spruce budworm y.rould have been much greater. Thinning will
increase the probability of wind/snow breakage in grand firs; however, the
broken grand firs will be very small and will not have a marked effect on
the stand's structure. Thinning will initially reduce stand susceptibility to
western spruce budworm by reducing basal area. If thinning results in an
....
tj
FIGURE 5. Projections of some "old growth" structural features in multiple canopy strata stands following different silvicultur­
al regimes. Darkened area shows presence of feature.
·
"'''' "''
";
'
;r
LOH DENSITY SYSTEM
HO ACTIVITIES SYSTEM
C:>.liOPY STJI.OCTITRB
'90
100
'10
120
'JO
'40
' 9 0 100
'50
'10
'20
1 J O 1 4 0 150
H I G H DENSITY S Y S T EM
190
100
'10 .120
'JO
140
150
ooro
:
groood ••g•<•<io
FOLIAGE DEPTH:
>100
tt.
>50 tt.
BAS/..L AREA
>300
,.200
>100
tt?
tt2
tt2
•••••
.-_,
KA.t , D I1J<rl' !:R
>19 in
>11 in
B
OB
. m
' DOWN LOGS
"' ""' , . .
- >10/acra
.
·
.
1-10/acre
.
, · H D SHAGS > llin
>10/acre
1-10/acre
DOHH
"''"'""
>BOO!t/acre
1-BOO!tfacrs DOHH LOGS> l lin
>BpOtttacre
1-BDD!tfacrs
....
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_,
:
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,­
.
.
,
.
,
-
••
•
i
....:.\ - f
..-,_.:--�,..;_._
374 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
FIGURE 6. 60-year, stand silhouette projections showing structural features
typical of dense, single cohort stands (referred to here as "pole"stands) under
different silvicultural regimes. Low.p nsity =Multiple Strata Regime (Scale
on left (in feet) represents both horizontal and vertical); Black crown = Doug­
las-fir; White crown =grand fir; Spotted crown =ponderosa pine.
1 so I•
00 •.
NO ACTIVITIES
,: MID-iii
1990
.
2010
.•
150
2030
· .·
MULTIPLE C ANOP'( STRATA
100
'"!Iii 11WIIiillf·�
0
199Q
..
,, 10or
._
HIGH DENSITY
·:.·,'
1990
.
2010.
'
150
0
2050
I
-
, -·
'
.,
.·
2010
2030
2050
• ':ltr•ll•
lLlJ!I;1i ll:jtt-JJH€R
2030
2050
increase in grand firs in the understory, however, stand susceptibility to
budworm will increase over time. This trend could be reduced if thinning
was heavy enough to favor growth of nonsusceptible species (e.g., ponder­
osa pine). Creating a multiple canopy structure in dense y oung stands will
substantially reduce the susceptibility of the stand to wind/snow and in­
sects. After four to five decades, the grand firs will become susceptible to
Oliver et al.
375
wind/snow breakage; however, these trees will be very small and will have
little impact on stand structure.
Where silvicultural activities kill trees but do not remove any of them
(to create more snags and logs for "old growth" habitat), both multiple
canopy and dense single cohort stands will become extremely susceptible
to fires. This extreme susceptibility would also occur where trees were
killed by the common wind/snow and insect disturbances (Figure 3). Re­
moving most or all of the killed trees during the silvicultural operations or
performing other silvicultural treatments to remove fuels can dramatically
reduce the stand's susceptibility to fires (Figure 4).
Effects of Timber Removal
D u ring Silvicultural Treatments
Stand Structures-If all merchantable trees are removed in thinnings, the
absence of snags and downed logs will be the most noticeably changed
structural features. If twigs, foliage, and buds are not removed, the nutrient
losses will be minimal. Only y oung, small snags and very old snags will
then be present, since most large trees will be removed before they die.
Old down logs will eventually disappear, and few new down logs will be
recruited. To provide these features in the future, some trees would need to
be designated and left for snag and down log recruitment.
It is highly unlikely that all trees killed in the silvicultural treatments
will need to remain in the forest for snags and for down logs. For example,
some treatments will create nearly 1,000 snags per acre. At the end of 60
years, there will be over 10,000 linear feet of down logs per acre with
some regimes. Evenly distributed, these forests would contain a down log
every 4 feet across the forest floor. Since most of a tree's timber value is in
the lower one third of the bole, removing this portion and leaving the top
as a down log may be a cost-effective way of producing down logs,
provided the top is large enough to serve structural purposes. Removing
some of the trees during thinnings and lopping the tree tops and branches
to ensure contact with the soil and rapid decomposition will markedly
reduce fire susceptibility.
Costs-If no silvicultural activities are done in the stands, the primary
direct costs will be fighting and recovering from the catastrophic fires
which will occur with or without preceding wind or snow breakages and
insect disturbances. If active silvicultural treatments are imposed and no
timber is removed to offset their costs, the different regimes will require
between $742.00 and $1,515.00 per acre (not discounted) over the next 60
years to implement (Table 3). Where thousands of acres are to be sustained
for old growth and no timber is removed, millions of dollars will be neces­
• -
.,;Q!l 'M
>lll'..,.WJ"Miii"""¥"'W%'i'":!rdi:Xi"''''".,.Ql:"..'"''hl
-'-'--'--'-��,-);1!'""-•;gy:;;.·•.,.., ··p '$Q.f:(• -;·· ••.l'.e;....,.· --a•;.;-:.1Jf•i·'-":jtfrl(.1i;,-.;:• .,�"iWJ.S'(&;-
;;; -- '"''�4:
-
::-.""".
'·t>··
-::-"�...-ax=�s--:::w
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376 ASSESSING FOR EST ECOSYSTEM HEALTH IN THE INLAND WEST
w
a:
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(.)
5
o
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(.)
:;::
u..
(.)
30
u::
20
0
;!
w
a:
i
(.)
a:
"5:
2000
;
2010
;
2020
2040
w
::r:
(.)
(/)
(/)
<
.J
(.)
2050
DATE (YEAR, A.D.)
w
N
Ci5
>­
m
40
w
a:
5
30
a:
....
a:
w
20
::>
-::r:
m
0
u::
0
z
<
a:
(!)
m
10
2010
2020
2030
2040
DATE (YEAR, A.D.) , - MULTIPLE CANOPY
I.Jc
1000 [
,:
TC
2050
T CT
N"
m
2000
1990
z
0
<
z
(/)
I
2000
======== =----------------
- HIGH DENSITY SYSTEM
50
(i)
377
L.
- NO ACT'VITIES
"',"":=-=-=I
203Q
--'....-:-
140r
120
I
1001.
.
I
\
'
801\
---· -- · \ --------60 �"'·'·
-------- --------. \'.
40 '
-----------20 .
;'
\I
'{
0
1990
2000
2010
2020
2030
2040
2050
F ---- ·
z
40
::r:
m
0
.. ;:
0liver et a/.
FIGURE 7. Projections of species diameters, and percent crown closure,
hard snag numbers, and down log lengths for dense, single cohort stands
(Figure 6). (Diameters show largest tree of each species and stand. Snags
and logs are in 3 diameter classes. N No Activity Regime; C Multiple
Strata Regime; T
High Density Regime. Snag & down log scales are
logarithmic.
50
=
---- i.:&.{ii·J,.·,-:z -,0-�-spv�q
CT
N
2010
:'
N
2020
c
2030
T
T
N c N c
2040
2050
DATE (YEAR, A.D.) •
19" DBH
B
-
OVER
CJ
UNDER 111NCHES DBH
11 to 19 INCHES DBH
DATE (YEAR, A.D.)
s
o
40
::r:
m
0
30
20
(;3
w
0
z
0
c..
10
;:u1ooooo
a:
r
w
w
u..
[
TC
;::: 10000
L ==-=--=---
j
I
-
(!)
0
.J
z
--0 --------- ------ ------__j
2000 -- 2010
1990
2020
2030
2040
2050
DATE (YEAR, A.D.)
-NO ACTIVITIES
....
(!)
z
HIGH DENSITY
-MULTIPLE CANOPY
:;::
0
0
1000
TC
rc N TC N
N.
·I·
100
10
1990
2000
·
'}"
..:
..
··
.
:-·
.•
··::
-
2010
:
I
2020
N
rc
2030
T
c
-
N
2040
DATE (YEAR, A.D.)
19" DBH
-
OVER
CJ
UNDER
11 INCHES DBH
-
11 to 19 INCHES DBH
rc
N
2050
-------2
378 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
FIGURE 8. Projections of susceptibility of dense, single cohort stands fol­
lowing different silvicultural regimes to destruction by common wind/snow
and insect disturbance agents. Susceptibility of 100 extreme likelihood
of disturbance. Susceptibility values over 200 were assigned a value of
200. Wind and snow susceptibility listed by species. [] No activities re­
gime; + High Density Regime;
M ltiple_ Strata Regime.
WESTERN SPRUCE BUDWORM
200
=
150
=
=
* =
PONDEROSA PINE
WIND/SNOW
.
200
1-
150
1001-
5"-
-----------0
1990
2000
2010
---2020
-2030
-------2040
2050
.w
,Q
z
.. - <1:
c . IXl
w
u
z
<!
IXl
0:
::l
l­
en
c
0
1>!:::
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IXl
i=
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u
en
::l
en
100
·
·
-----
5
2000
2040
2030
26'io
2010
-_j
2050
MOUNTAIN PINE BEETLE
200
150
100
DOUGLAS-FIR WIND/SNOW.
·c:
::1
1c
0
1-
379
0 liver et al.
50 f-
l •, '
*E
liE
)(
)(
�(
)(
)(--j
0 �------�
1990
2030
2000
2040
2020
2050
2010
*
10
..
'>::::
..
--1
DATE (YEAR, A.D.)
::::i
IXl
i=
a..
w
0
en
::1
en
sary to create and maintain suitable habitat. These costs do not include the
2000
2010
2020
2030
2040
2050
direct costs of fighting and recovering from catastrophic f'rres and the
indirect costs of losses of habitat and water quality following f'rres.
If all merchantable timber is removed in the silvicultural treatments, the
different regimes will yield a return of between
$1,215 and $14,042 per
3 and Figure 10). This
acre (not discounted) over the next 60 years (Table
GRAND FIR WIND/SNOW
return does not include the direct and indirect savings created by avoiding
catastrophic wildf'rres and unemployment.
----
10
1-
u
Removing trees as forest products can reduce costs of implementing the
various systems-or create a monetary gain-as well as reducing the stand's
susceptibility to f'rres (Figure 4). Removing some trees for forest products
and leaving others for wildlife habitat could bring enough revenue to
cover the costs of creating habitat while reducing f'rre danger. Wildlife and
ecological expertise will be necessary to determine the appropriate num­
2000
2010
2020
. 2030
DATE (YEAR, A.D.)
2040
2050
bers of snags and down logs to leave.
r, ·.:
' f
u.
0:>
0
'[
i
I .
'
,,
·I
·\
F I GURE 9. Projections of some "old growth" structural features in dense, single cohort stands following different silvicultur­
al regimes. Darkened area shows presence of feature.
cANoPY
un:�s
190
r 111ora
:
ground vagotatio
FOLIAGE DEPTH :
>100 t t.
> 50 t t .
BASAL AREA
MULTI P L E
N O ACTIVITIES SYSTEM
BTRDCTOll ll
CA!IOPY
2
> 3 00 tt
1 00
110
'20
'30
'40
'90
'50
'00
CANOPY
'10
STRATA SYSTEM
'2 0
'30
'40
'50
H I G H DENS ITY
'90 1 0 0
'10
'20
•,Q
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it
l,
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'40
'·
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f1.
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2
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!il
2
>100 t t
I
[
MAX , DUX�l!:R
>11
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H D SNAGS > 1
HD
SNAGS
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DOWN LOGS > l 9 i n
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1-BOO!t/acre
""'" "''''''''
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382 ASSESSING FOREST ECOSYSTEM
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FIGURE 10. Living (line) and dead volume (block) by time for multiple
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canopy stands and den se stands, single cohort and silvicultural regimes in
eastern Washington. Removing some volume would reduce risk of fire and
provide a montary returo or offset the costs of silvicultural activities to create
old growth structures.
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Effects of Silvicultural Activities
With andWithout Removal of Timber
Avoiding all treatments in the multiple canopy stands will maintain
some "old growth" structural features, but will not allow others to be
achieved for many decades. In addition, most stands will probably bum­
with or without preceding western spruce budworm or mountain pine
beetle outbreaks.
Avoiding all silvicultural treatments in the dense, single cohort stands
will ensure they will not be suitab le habitat for old growth species for the
next 60 years. Some stands will become susceptible to wind and snow
breakage, which can lead to insect outbreaks and fire. Other stands will
first become susceptible to the western pine beetle and, afterwards, rrre.
Still others may burn without previous wind, snow, or insect distur­
bances.
Appropriate silvicultural treatments such as thinnings or "uneven-age "
harvesting will create many of the "old growth" structural features more
rapidly than by avoiding management These treatments can reduce the
susceptibility of the stands to wind, snow, and insect disturbances; howev­
er, the stands will become extremely susceptible to fires if some wood is
not removed (and the slash treated appropriately).
Silvicultural treatments which remove some wood for forest products
will be more effective in both providing greater amounts of "old growth"
structures and reducing risks of stand destruction than either avoiding all
management or doing silvicultural treatments without removing timber.
Removing timber for wood processing can also make creation of "old
growth' structures financially profitable, or at least reduce the costs of
producing the s tructures (Lippke and Oliver 1993).
Other silv cultural treatments are also possible, but were not simulated
here. For example, tree tops can be removed with dynamite or a chain saw
to create snags which rot differently from girdled trees. Hollow, living
trees can be created by scarring living trees. Understory density and spe­
cies can be manipulated by scarifying the forest floor, although little
understory vegetation will grow if the overstory is extremely dense. Some
forms of "nest platforms " can be constructed in trees if such structures are
helpful for endangered species (e.g., the spotted owl). Other silvicultural
regimes can also make the stands less susceptible to various disturbance
agents at various times.
The actual silvicultural treatments can be done during seasons when the
old growth species would be least disturbed. Each treatment described in
385
Oliver et al.
384 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
DISCUSSION
J:.
_ __
this paper will occur about once every twenty years in a given stand and
last for one day to two weeks, depending on the technique . Each s tand,
therefore, will be disturbed for 0.013 to 0.19 percent of the time by these
silvicultural treatments .
Landscape Management
There is no single silvicultural regime (including avoiding all activities)
which will create and maintain a structure ideally suited for old growth
species thloughout time. The structural features · will change under each
silvicultural regime, with some useful features becoming present as others
decline. In fact, it is probably not biologica lly possib le to have and main­
tain (t hrough natural or artificial means) a stand which will be perpetua lly
ideal "old growth" habitat. Structural features useful for old growth spe­
cies can probably best be achieved in a forest by maintaining a mixture of
stands across a landscape , with the structural features developing in differ­
ent stands at diff erent times (Oliver 1992). -This mixture will also keep
large areas from developing susceptib ility to a disturbance agentand being
destroyed at one time. It will probably be necessary to do stan d-replace­
ment harvests (varieties of chiarcut, shelterw'ooo , and seed tree harvests) to
some stands to maintai:O. open habitats (Young 1992) where natural distur­
bances do not create sufficient amounts across the landscape.
Each active silvicultural regime will create some structural features of
old growth at some times . Doing no silvicultural treatments will generally
create the fewest old growth features where the features do not presently
exist and may leave stands susceptible to various disturbances in the long
term. Which regime is used on a given stand will depend on the present
mixture of stand structures across the landscape, how this mixture will
change with time , and what is the desiied distribution of structures across
the landscape. It will probably be appropriate to prescribe different silvi­
cultural regimes for different stands within a landscape so .that different
stands produce desired structural features and avoid becoming susceptible
to disturbances at different times . This " landscape management " will
keep various "old growth" and other structural features available within
the landscape as a whole at all times (Boyce 1985).
·
Practical Considerations
Ma intaining a variety of stand structures across a landscape while re­
moving timber, with each stand developing to certain structural features
at different times , will also have practica l advantages . Silvicultura l treat-
.
....-- "'--'"'.:<"J
386 ASSESSING FOREST ECOSYSTEM HEALTH IN THE INLAND WEST
Oliver et al.
387
-
ments required will be diversified and staggered, so a relatively constant
work f9rce and budget can be maintained. Also, any products removed
will flow at a relatively steady rate to provide steady manufacturing
employment. The wood produced will provide an environmentally sound
substitute for more polluting steel, aluminum, brick, or concrete (Ker­
shaw et al. 1992) or for wood produced from regions of the world with
fewer env_ironmental safeguards. Finally, the diversity of stand structures
and times .of treatments will reduce the risk of catastrophic distUrbances
caused by synchronous buildups of fuels ·or insects across a large land­
scape.
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.• .
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Stage, A.L. 1 973. Prognosis model for stand development. USDA Forest Service
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