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T)~ees-- TIle
Lillk Betweell Silvicultllre and
Hydrology
Merrill R. Kaufmann, Charles A. Troendle, Michael G.
Water and timber are fore~t products that result from
complex processes at the watershed, stand, and tree levels.
Subalpine forest ecosystems, whic.h are considered here. to be
equivalent to stands or small catchments, receive inputs of
energy, carbon, water, and nutrients. Within the ecosystem, a
wide array of processes involves conversions and exchange of
these components. The net r~su1t of these processes and
transformations affects the quantity of water available for
streamflow and biomass production, induding merchantable
bole volume.
The study of processes involved in water and biomass
production from subalpine forest ecosystems often requires
research on isolated components of the ecosystem. Yet, an
understanding of ecosystem behavior also requires that all the
components be. considered together, because all of the processes and components of the. ecosystem interact to produce the
observed outputs.
Tre.es playa crucial role in ecosystem behavior, because a
major portion of energy, carbon, water, and nutrient exchange
in ecosystems are influenced by or occur in trees. At the level
of forest stands, for example, the canopy intercepts energy and
influences air movement, thereby affecting photosynthesis,
transpiIation, and the thermal and light environment of the
forest stand. An existing stand represents the current status of
competition for energy, water, and nutrients.
At the leve.l of foliage, carbon is fi.'"{ed by photosynthesis,
some of it stored in wood or other portions of the biomass until
harvest or death, some utilized for foliage or fine roots having
a shorter lifetime than that of the tre.e, and some utilized in
respiration. Also in foli~lge, water absorbed by tree roots is
transpired and returned to the atmosphere as vapor. And
finally, nutrients continually are absorbed and used for growth
or returned back to the forest floor by foliar leaching or loss
of plant tissue.
The gas exchange processes of the foliage provide one link
between silvicultural and hydrologic phenomena. CO? enters
foliage through stomata, and water leaves the foliage through
the same stomata (fig. 1). Thus, dry matter production, the
essence of timber productivity, and transpiration, a major
com~onent of the hydrologic. cyc1.e, are simultaneously de··
Ryan, H. Todd Mowrer 1
pendent on stomatal behavior. This paper focuse·s on how
trees influence various aspects of the water and carbon cydes,
and discusses how tree processes are involved in subalpine
forest hydrology and silviculture.
Papers by Smith, Meiman, and Troendle and Kaufmann
(this volume) discuss related aspe.cts of silviculture and hydrology of subalpine forests in the central Rod:y Mountains.
Stottlemyer addresses the trends in input/output chemical
balances of the Fraser Experimental Forest watersheds.
TREES AND THE CARBON CYCLE
Carbon fixation by tree·s is the sole source of dry matter for
wood production, except for very minor amounts of nutrients
found in woody material. While photosynthesis by the understory vegetation may be substantial in some forest types and
may be important in forage production, it does not contribute
to commercial wood production.
Carbon fixation depends upon a number of factors. The.re
is reasonably good evidence that, for young stands, biomass
productivity is nearly linearly related to interception of radiation (Linder 1985). Radiation interc.eption is dependent on
day length, slope and aspe.ct, shading by c.ompeting vegetation,
and the arrangement of foliage within a crown. For a given
physiographic location, optimal stand productivity depends
upon the canopy being configured in a way that maximizes
light interception while guarding against the negative effects
of over-crowding, whic.h may lead to carbon allocation away
from harvest able. product. Silvicultural rese.arch (e.g., Alexander 1986a, 1986b; Alexande.r and Edminster 1980, 1981) has
been conducted to maximize timber productivity using an
empirical approach to density c.ontrol that effectively optimizes radiation interception for a given site.
The volume growth of a tree depends not only upon how
much energy the tree crown captures and upon factors affecting photosynthesis through effects on stomatal behavior, but
also on the allocation of the newly fi.~ed carbon. Within trees,
carbon may be all.ocated to stem dry matter production,
replacement of foliage and fine roots, or maintenance respiration. The "harvest index,'·' the proportion of stemwood to
total tree biomass, is one measure of long-term effe.cts of
annual carbon allocation. \\Taring and Schlesinger (1985)
Research Forester, ResE~arch Hydrolcgist, Statistician, and Research Forester, Floc~(y Mountain Forest and 11ange Experiment Sta.tion,
Headquarters is in Fort Collins, in cooperation with Colorado State
University.
54
CARBON CYCLE IN TREES
HYDROLOGIC CYCLE
CO, Return to
CO, from
Water Loss
Water from
Atmosphere
Atmosphere
to Atmosphere
Atmosphere
\
TransPira:{,
Stomata
~
Photosynthesis
/'
Maintenance
Respiration
/
~
Interception
I
Photosynthetic
Uptake by Plant
Products
~
1
Root and
Stem and
Leaf Turnove:.
Branch Growth
~
Surface and
Streamflow
Soil Storage
Figure 1.--Simplifled carbon and hydrc)loglc cycles. Photosynthesis and transpiration involve the exchange of CO 2 and water vapor through stomata.
hypothesize that there is a hierarchy of priority for receiving
newly fixed carbon, and stemwood is generaUy produced only
after demands by foliage and fine roots have been met. An
understanding of allocation processes therefore may help
determine how management practices can alter the harve,st
i.ndex.
There is increasing evidence (Grier et aL· 1981, 1982;
Linder and Axelson 1982) that fine root production represents
a major sink for newly fixed carbon. Fine roots (including
fungal symbionts) are very important for both water and
nutrient uptake, and above.ground production may de.pend
more on how such carbon is used by fine roots than on
differences in assimilation. Thus, silvicultural practices, such
as thinning and fertilization, may increase the harvest index
because of decreased allocation to fine root production rather
than increasing net assimilation.
eurre.nt empirical prediction models provi.de estimates of
timber and water production on a par wi.th our present ability
to measure them. ~Thile empiricisms are seldom the best
possible estimators of tree or stand performance and interaction, estimators specific to each microprocess within a tree are
likely to involve too much inherent variability for accurate
prediction when aggregated to a stand level. Knowledge of
carbon balance and carbon allocation in subalpine species is
very limited, however. Additional research on the carbon cycle
in subalpine trees may refine our understanding of the effects
of stand structure, site, and environmental conditions on tree
growth. Enhanced knowledge of these microprocesses within
the tree and their effect on macroprocesses within the ecosystem will certainly provide guidance to improve predictive
relationships at the tree and stand level.
Kaufmann and Ryan (1986) examined the growth rate of
individual subalpine conifer trees. They determined that volume growth is influenced by energy capture, which is a
function of leaf area, but concluded that other factors also
were i.m portant. Thei.r data showed that the growth effi.ci.ency
of trees (volume growth per unit absorbed radiation) was
different among species and varied with tree age. Efficiency
was notably different between lodgepole pille, an intolerant
species, and Engelmann spruce and SUbalpine fir, both tolerant species (fig. 2; also see Ryan, this volume). The growth
efficiency of pine was much higher during the first 100 years
than that for spruce and fir, but it declined to the spruce-fir
levels in about 200 years.
It may be hypothesized that tree volume growth and growth
efficiency depend, in part, upon the amount of new photosynthate that i.s utili.zed in maintenance respiration, and that the
maintenance respiration requirements depend on the respiratory biomass existing in the tree. Ryan (this volume) reports
that the amount of sapwood supported per unit leaf area varies
among species, and he is currently conducting studies on the
sapwood respiration rates of pine and spruce of varying sizes
and ages. These studies may be helpful in reaching an understandi.ng of the balance and allocation of carbon in subalpine
conifers, and they may provide a basis for evaluating limitations of growth caused by inadequate water or nutrient availability.
TREES AND THE
If~'DROLOGIC
CYCLE
The hydrologic cycle of an ecosystem includes water input
as precipitation (snow or rain), movement within the ecosystem (often involving a change of phase from snow to liquid
water and from liquid to vapor), and output in the forms of
55
a
Engelmann Spruce
b
Subalpine Fir
c
Lodgepole Pine
o
~o
• Azimuth 90 to 270 deg
o Azimuth <90 or >270 deg
o
w
.r:
~
2
~
2.0_
@
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o ~
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~
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CI:
cf] •• o
o.ct
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. • .. a •
C§}J
°-.:Xo
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200
400
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00
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<i' I2P ' ••• ~rS1(
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L--_--'---_-..::L_--=-.L...---!.-l
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0
0
0
'3
0
•
• 0:
200
o• • ~~8...~p
•
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200
400
Age (yr)
Figure 2.--Relatlve grow1h efficiency as a function of tree age and aspect of the site for (a) Engelmann
spruce, (b) subalpine fir, and (c) lodgepole pine. The relative growth efficiency Is a measure oftree
volume grow1h In relation to potential absorbed radiation.
attributed to effects on total annual ET, because the gross
annual precipitation and percolation to groundwater (if any)
are not likely to be affected by stand density. In a review of the
use of forest management techniques to increase the yield of
water from subalpine forests, Troendle (1983) provided evidence indicating that water yield augmentation re.suited from
stand harvesting effects on both summer ET and winter
snowpack accumulation. ~feiman (this volume) reviews evidence that the snowpac.k water equivalent in harvested watersheds is increased because of a reduction in sublimation when
stands are thinned or clearcut. Troendle and Kaufmann (this
volume) address the effect of stand density on both total
annual water yield and on growing season soil water depletion
rates.
Annual ET of subalpine forests has several components.
Variation in these com ponents through the year and as a result
of stand manipUlation makes ET both dynamic. and very
complex. During the summer months when no snow exists,
stand ET indudes overstory transpiration, understory transpiration, and evaporation of water intercepted by the vegetation
and the litter and soil. During the winter, stand ET is com posed
primarily of evaporation from the snowpack and evaporation
of snow intercepted by the forest canopy. The generally frozen
conditions prevent transpiration by the trees. During the
transition periods of spring and autumn, transpiration by the
overstory varies widely with weather conditions. Snow cover
during these periods is incomplete or transient, and ET
beneath the overstory occurs as evaporation from the snowpack and litter, transpirati.on from the understory vegetation,
or both. Interception losses duri.ng thi.s period include evaporation of both rain and snow.
water (streamflow) or water vapor (evapotranspiration or
ET). Associated with the movement of water is the movement
of chemicals, both those entering and leaving the ecosystem
and those c.yding within the ecosystem. Trees absorb water
and nutrients from the soil. Through transpiration they release
water to the. atmosphere, and through foliage le.aching and
foliage and root turnover they release some nutrients to the soil
and litter. Trees also intercept significant quantities of water
that evaporates without entering the soil-plant system, and
they intercept chemicals from the atmosphere, both in precipitation and as dryfall.
Streamflow from forested ecosystems depends upon the
total precipitation received and the amount lost from the unit
as ET, plus any amount that percolates directly into the
groundwater supply. Trees have a direct influence over the
amount of precipitation input available for streamflow, because they (1) transpire water, (2) intercept water that is
evaporated or sublimated directly back to the atmosphere, and
(3) modify the. understory ET environment.
Water yield from subalpine forests in the central Rocky
~10untains is very important in the 'Vest, and considerable
attention has been given to the effects of stand management
on wate·r yield from subalpine watersheds. ~1any studies have
indicated that the annual yield of water may be increased by
stand manipulation. Three watershed experiments in Colorado have demonstrated increased water yield after harvest
(Wagon \\Theel Gap, Fool Creek, and Deadhorse Creek--see
Troendle 1983). The Fool Creek experiment continues to
demonstrate increased stre.amflow more than 30 years after
harvest. Furthermore, calculations based on time-s~ries analysis of the dedine in increased streamflow, on the dedine in
winter snowpack accumulation, and on projected increases in
tree leaf area index (LAI) in the harvested areas, all indicate
that the increase will not totally disappear (return to pretreatment streamflow) until 70 to 80 years after harvest (Kaufmann
1985a, Troendle 1983, Troendle and King 1985).
1\10st effects of stand manipulation on water yield may be
Summer
ET
The principal pathways of water loss for the overs tory,
understory, and ground are shown in figure 3. Each compo-
56
Onrstory Transpiration
nent of summer ET i.s influenced by the type and structure of
the forest stand occupying a site. Most evidence suggests that
during summer months, ET in the subalpine forest exceeds
precipitation and results in a moderate soil. water deficit.
Troendle (1987) recently showed that in an uncut area, soil
water depletion exceeded summer precipitati.on, resulting in
soil water deficits. Flow into a subsurface collection system at
the base of a forested slope occurred only in the spring after
snowmelt satisfied recharge requireme.nts. Recharge requirements on a nearby deareut plot were substantially less. Subsurface outflow from the dearcut occurred after a significant
summer rainfall or in early autumn when ET was reduced,
indic.ating that 1% or 2% of the summer rainfall may directly
become streamflow following timber harvest.
Overstory transpi.ration is directly related to the atmospheric. evaporative demand, but i.t also is influenced by LAI
and stomatal behavior (Kaufmann 1984a, Kaufmann and
Kelliher in press). At equivalent stand basal areas, LAI varies
greatly depending on the species composition of the stand
(Kaufmann et a1. 1982). Furthermore, stomatal behavior also
varies among spedes, such that for e.quivalent environmental
conditions and basal areas, stands of different species may
have widely different tree transpiration rates (Kaufmann
1985b). I)hysiograph~c characteristic.s of the site (slope, aspect, and elevation) also influence overstory transpiration
through effects on light, temperature, and humidity within the
forest canopy.
These results illustrate the importance of the forest canopy
in affecting summer ET. A forested site utHized both summer
predpitation and some of the water stored in the soil, resulting
in soil water depletion during the summer months. In an
unforested site, however, the understory vegetation utilized
much less of the stored soil water, resulting in a 2.5- to 3-inch
(6- to 8-cm) re·duction in soil water depletion. This allowed
large storms duri.ng the summer and precipitation in the.
autumn (when ET demands were lower) to create a surplus,
resulting in outflow from the dearcut. Since more than 95(10 of
the measured flow increases occur during the spring snowmelt
period, the subtle growing season changes observed at the plot
level are not easily detected at the watershed level. Howeyer,
Troendle and Leaf (1980) noted that flow increases can occur
any time precipitation i.nput (rain or snowmelt) exceeds the
recharge requirements in the cutover area (also addressed in
Troendle 1983).
Understory ET
Overstory stand density and species composition also may
affect understory ET. Differences in tra.nsmission of irradiance by the over~tory affect how much energy is available at
the forest floor for understory ET. Light transmission of
subalpine forest sta.nds is a function both of LAI and of leaf
area dumping within crowns (unpublished data, Oker-Blom,
Ryan, and Kaufmann). At equal stand densiti.es, the LA! for
lodgepole pine and aspen stands is considerably lower than for
Engelmann spruce-subalpine fir stands. Differences in light
transmission to the forest floor may influence the understory
species composition and vegetation density, as weU as the
environmental conditions regulating ET.
Overstory densi.ty and structure affect aerodynamic mL~­
ing in the forest stand, and this may affect ET processes. Most
Water Sources
Vapor Losses
Overstory
Interception
Foliage
Sapwood
Overstory Et
Overstory E i
Understory
Intercept ion
Foliage
Below Ground
Soil
Roots
Understory E t
Understory E i
Litter EI
Soil Es
Figure 3.--Water sources and a.venues by which watln vapor is lost fr()ln a fl)rest. EvapI)transplration
(shown hem as E) ma.y occur through transpiration (subscrlptt) from thl~ OVI!rstOI'Y and undel'story
vegetation, through evaporation of Intercepted water (subscript i), and thl'ough evap0l'ation fl'om
litter and soil (subscripts I and s).
57
evidence suggests that air in the overstory of conifer stands is
well mixed, and as a result transpiration is regulated primarily
by stomata and the vapor gradient (J an'is 1985, Kaufmann and
Kelliher in press). Lower in the canopy, however, mixing is
poorer. As a result, the microenvironmental conditions existi.ng at the. understory level depend much more on the radiation
envi.ronment than they do in the overstory. This is evidenced
by the much warmer temperatures of air and soil on southfacing slopes than on north-facing slopes during midday
(Noble and Alexander 1977), even though canopy temperatures of the overstory seem to be relatively unaffected by
radiation input (Kaufmann 1284b). Furthermore, canopy
density and the. re.late·d aerodynamic mjxing may differ with
aspect, with north aspects typically having a more dense
overstory than south aspects. .
As a consequence of these overstory effects on the distribution of radiation and on aerodynamic mixing, the density
and structure of the overstory may play an important role not
only in affecting overstory transpiration, but also in regulating
understory ET. ""hile data are not available, it is quite possible
that tree harvesting techniques that result in different patterns
of leaf area di.stribution in the overstory (I.e., partial harvest
versus patch cutting) could alter understory ET even though
they result in the same total residual stand LA!.
structure and composition may have complex effects on ET,
because several components of ET may be changed.
Considering overstory transpiration alone, transpiration
apparently is affected by LAI, and it varies widely among
spedes at the same stand basal areas (Kaufmann 1984c,
1985b). But within a species, a change in stand density and LAI
influences interception of precipitation by the overs tory, the
transmission of light to the understory, and perhaps water
availability for growth and transpiration by understory ve.getation. Similarly, the differences in LAI among species at
similar stand densities may affect interception and understory
ET processes.
For example, the unde.rstory vegetation bene·ath spruce.-fir
stands is often fajrly sparse, whereas beneath aspen stands the
vegetation is freque.ntly dense and lush. Estimated branch
transpiration rate.s for aspen were considerably lower that
those for spruce-fir, suggesting that less soil water was extracted by aspen than by spruce-fir (Kaufmann 1985b).
However, the aspen measured were in mbced stands rather
than in pure stands. In pure stands, a well-developed aspen
understory may use considerably more water in ET than a
spruce-fir understory because of higher light transmission,
better development of the vegetation, and higher availability
of soil water. Consequently, some of the savings by the aspen
overstory may be offset by increased losse.s from the understory. Limited data from the Fraser Experimental Forest
indicate soil water depletion rates under various densities of
aspen are similar to those under similar densities of lodgepole
pine.
Interception
Rainfall interce ption by the overstory is affected by the size
and duration of storm e.vents, but interception depends as well
upon the surface area on which water can accumulate. ",'ilm
and Dunford (1948) measured precipitation in openings and
beneath lodgepole pine stands of varying density and observed
interception losses by the overstory of 7% to 32% of precipitation during July, August, and September. Reynolds and
Knight (1973) observed that throughfall was 79% of precipitation for four lodgepole pine stands, compared with 60% for
four spruce-fir stands (equivalent to interception rates of 21~,
and 40%). Interception in both of these studies appeared to be
positively correlated wi.th LAI.
Interception by the. understory and litter also prevents
rainfall from reaching the rooting zone of the trees. Reynolds
and Knight (1973) obse.rved that the water-holding capacity of
u.tter was about 125% of the litter dry weight in both lodgepole
pine and spruce-fir types. It also is possible that, in harsh sites
where mineral soil is exposed, intercepted water in the upper
few centimeters of soil may be unavailable to trees because the
absorbing roots are deeper under these conditions.
As another exam pIe of the complexity of relating total ET
to stand conditions, a reduction in basal area by partial harvest
versus patch cutting may be considered. When LAI is reduce.d
over an entire stand by uniformly distributed tree harvesting,
light transmission to the forest floor increases, favoring increased ET from the forest floor. In a dearing created by
re·moval of the same basal area in patches, the exposed forest
floor receive·s the entire radiation input and probably has
higher aerodynamic mixing, thereby favoring substantially
increased ET than for the understory vegetation in the uncut
portion of the stand or in the partially harvested stand. In
addition, changes in the amount of understory vegetation may
influence the relative losses from transpiration and evaporati.on from the forest floor or dearcut. The net effe.ct of these
differenc.es on total ET of the two stands is not known.
Research is being conducted on each component of ET,
with the goal of developing and testing techniques for estimating the ET components independently. If successful, this
research will provide methods for assessing how total ET may
be manipulated through stand trea.tment. Furthermore, this
research may bring us closer to the ability to estimate each term
of the hydrologic cycle i.ndependently without obtaining any
component by difference ("closure"), and it may facilitate
relating summer hydrologic processes to processes important
in tree ecophysiology and in nutrient cycling.
Off-Setting Conditions
It is clear from this discussion that a number of factors,
which may vary naturally or as a result of management
activities, can affect the ET processes occurring during the
transpiration season. It also is obvious that changes in stand
58
WinterET
Alexander, Robert R.; Edminster, Carleton B. 1980. Management of spruce-fir in even-aged stands in the central
Rocky J\.fountains. Res. Pap. RJ\.f-217. Fort Collins, CO:
U.S. Department of Agriculture, Forest Service, Rocky
J\.fountain Forest and Range Experiment Station. 14 p.
Alexande.r, Robert R.; Edmjnster, Carleton B.1981. Management of lodgepole pine in even-aged stands in the central
Rocky Mountains. Res. Pap. RM- 229. Fort Collins, CO:
U.S. Department of Agriculture, Forest Service, Rocky
J\.fountain Forest and Range Experiment Station. 11 p.
Winter water vapor losses do not appear to be as complex
as summer ET losses, although they are not well understood.
Winter losses in subalpine forests are primarily through sublimation of i.ntercepted snow (or evaporation of snow meltwater on branches if air temperatures are warm enough) and
sublimation of the snowpack Transpiration of trees is negligible during winter months because of stomatal inactivity and
freezing conditions in the soil-plant system.
Grier, C. C.; Vogt, K. A.; Keyes, M. R.; Edmonds, R. L. 1981.
Biomass distribution and above- and below-ground production in young and mature Abies amabilis zone ecosystems of the Washington Cascades. Canadian Journal of
Forest Research 11: 155-167.
Data summariz.ed by J\.feiman (this volume) indicate that
snowpack water equivalent can be Hllearly increased up to
30 1%or more as basal area is reduced, and a significant portion
of the annual increase in water yield associated with timber
harvest is related to the associated reduction in interception
loss. Consequently, LAI and the spatial distribution of foliage
in trees and stands influence winter interception and evaporation in much the same way they;affect summer interception
and ET. Effects on snowpack evctporation are not well understood, but it has been shown that energy input through air
movement and, to a lesser degree, solar radiation influence
winter evaporative rates in much !he same way they are
presumed to affect understory ET during the summer.
Grier, C. c.; Vogt, K. A.; Teskey, R. O. 1982. Carbon uptake
and allocation in subalpine ecosystems. In: Vlaring, R. H.,
ed. Carbon uptake and allocation in subalpine ecosystems
as a key to management: IUFRO workshop; 1982 August
2-3; Corvallis, OR. Corvallis, OR: Oregon State. University, Forest Research Laboratory: ~4-69.
Jarvis, P. O. 1985. Transpiration and assimilation of tree and
agricultural crops: the "omega factor". In: Cannel, 1\1. O.
R.; Jackson, J. E., eds. Attributes of trees as crop plants;
United Kingdom: Institute of Terrestrial Ecology, Natu~
ral Environment Research Council: 460-480.
SUMMARY COJ\.lMENT
Kaufmann, M. R. 1984a. A canopy model (R1\f-CWU) for
determining transpiration of subalpine forests. I. J\.fodel
development. Canadian Journal of Forest Research 14:
218-226.
Kaufmann, J\.f. R.1984b. Effects of weather and physiographic
conditions on temperature and humidity in subalpine
watersheds of thc~ Fraser Experimental Forest. Res. Pap.
RJ\.f-2S1. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range
Experiment Station. 9 p.
All aspects of forest management, for whatever intended
purpose, and all aspects of forest ecosystem behavior center
on trees as the main biological unit and on stands as the
organizational structure within which they function. Complex
and dynamic silvicultural and hydrologic processes are
thereby linked at the stand and tree level. An understanding of
these processes may be helpful in forest management and in
assessment of subalpine forest ecosystem function. Continued
research on tree and stand behavior will increase our understanding of all the biological and physical implications of stand
management and environmental change.
Kaufmann, M. R. 1984c. A canopy model (RJ\.I-CWU) for
determining transpiration of subalpine forests. II. Consumptive water use in two watersheds. Canadian Journal
of Forest Research 14: 227-232. Kaufmann, M. R.1985a.
J\.fodeling transpiration of subalpine trees in the central
Rocky Mountains. In: Jones, E. B.; Vlard, T . .T., eds.
Watershed management in the eighties: proceedings of
the symposium; 1985 April 30- May 1; Denver, CO. New
York, NY: American Society of Civil Engineers: 61-68.
LITERATURE etTEn
Alexander, Robert R.1986a. Silvicultural systems and cutting
methods for old-growth spruce-fir forests in the central
and southern Rocky J\.fountains. Gen. Tech. Rep. RM125. Fort Collins, CO: U.S. Department of Agriculture,
Forest Serviee, Rocky J\.fountain Forest and Range Experiment Station. 33 p.
Kaufmann, M. R. 1985b. Annual transpiration in subalpine
forests: large differences a.mong four tree species. Forest
Ecology Management 13: 235-246.
Alexander, Robert R.1986b. Silvkultural systems and cutting
methods for old-growth lodgepole pi.ne forests i.n the
central Rocky Mountai.ns. Gen. Tech. Rep. RJ\.f-127. Fort
Collins, CO: U.S. Department of Agriculture, Forest
Service, Rocky Mountain Forest and Range Experiment
Station. 31 p.
Kaufmann, J\.ferrill R.; Troendle, Charles A.; Edminster,
Carleton B. 1982. Leaf area determinations for subalpine
tree species i.n the central Rocky Mountains. Res. Pap.
RJ\I-238. Fort C~ollins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range
Experiment Station. 7 p.
59
Kaufmann, M. R.; Kelliher, F. 1\1. 198__ . Estimating tree
transpiration rates in forest stands. In: Lassoie, J. P.;
I-Hnckley, T.1\1., eds. Techniques and approaches in forest
tree ecophysiology. CRC Press. (In press)
Reynolds, J. P.; Knight, D. H. 1973. The magnitude of snowmelt and rainfall interception by Htter in lodge.pole pine
and spruce-fir forests in Wyomi.ng. Northwest Scie.nce 47:
50-60.
Smith, F. W. 1987. (this volume.)
Troendle, C. A. 1983. The potential for water yi.eld augmentati.on from forest management in the Rocky Mountain
region. "'ater Resources Bulletin 19: 359-373.
Troendle, Charles A. 1987. The potential effect of partial
cutting and thinning on streamflow from the subalpine
forest. Res. Pap. R1\I-274. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain
Forest and Range Experiment Station. 7 p.
Troendle, C. A.; Kaufmann, 1\1. R. 1987. (this volume)
Troendle, C. A.; King, R.1\1. 1985. The Fool Creek watershed-thirty years later. Water Resources Research 21: 19151922.
Troendle, C. A.; Leaf, C. F.1980. Hydrology. In: An approach
to water resources evaluation of non-point silvicultural
sources. Athens, GA: U;S. Environment Protection
Agency: 1-173.
"'aring, R. H.; Schlesinger, W. H. 1985. Forest ecosystems-concepts and management. New York, NY: Academic
Press. 340 p.
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