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Illfluence ()f Forests on Snowllack
Accunllliation
James R. Meiman 1
I
Abstract--There is ample evidence that both small patch cuts and thinning In..crease snow accumulation in the treated area. These effects extend
well beyond the approximately 50 years of record at the Fraser ExperImental Forest. The processes responsible are not yet precisely defined, but
reduced snow interception losses appear to be a major factor. There is no
evidence from recent studies at Fraser of significant redistribution from
forests to openin~ls during between storm intervals.
..
In the subalpine forests snow is the major source of wa.ter
supply and an important ecologiC-al factor. Thus a better
understanding of the processes that influence the accumulation, redistribution and ablation of the snow cover is essenti.al
for effective management of subalpine forests. This paper
focuses on the influence of forests on snowpack accumulation.
Other factors that influence. snowpack accumulation include
climate, topography and nonforest vegetation. Although a
brief review of literature on related studies is given, the
emphasis is on the work at the Fraser Expe.rimental Forest
whe.re the author has worked in association with the US Forest
Service over the past 20 years.
snow and removal of snow by wind. These two publications
provide an excellent set of references on snow interception
processes.
l\feiman (1970) reviewed approximately 70 North Anlerican studies on snow accumulation in relation to elevation,
aspect and forest canopy with emphasis on the subalpine and
montane zones. This review illustrated that although elevation
has a greater effect on snow accumulation on a large scale,
forest canopy can have a dramatic effect over very small
distances. Among the. studie.s reviewe.d that attempted to give
a quantitative relationship between snowpack water equivalent and canopy de.nsity, Packer (1962) reported a 0.42 inch
inc.rease per 10 perce.nt decrease in canopy, Lull and
Rushmore (1960) indicated a value of 0.33 inche.s, and
Kittredge gave. value.s ranging from 0.50 inches to 2.2 inches.
The study by Gary (1974) of snow accumulation as influenced by a small clearing in a lodgepole pine forest is relevant
to the Fraser Experimental Forest work because it wa.s located
in an area with similar climate and stand conditions. He found
an increase of approximately 24 percent in peak snow water
equivalent in a one tree height wide (lH) clearing. Further, he
found the excess water equivalent in the opening was nearly
equal to the deficit in the leeward forest zone. The author
commented that he could only conjecture as to the processes
responsible for the greater accumulation in the clearing.
Among the processes dLc;cussed were backed dies of the
airstrea.m during storms and/or redistribution from the leeward forest border during or following storms. An alternate
hypothesis wa.s that the greater snow in the clea.ring was offset
partly by greater loss by vaporization in the sun exposed lee
forest. The author did not discuss reduced interception loss as
a. possible cause of the increase.
In a follow up study Ga.ry (1980) increased the width of the
IH clearcut to 3H and 5H in consecutive cuttings. The width
Studies Related to Fraser Experimental Forest
Among the earliest recorded observations in the United
State.s on the influence of fore.sts on snow accumulation we·re
those made by Carpenter (1901), Church (1912), Jaenicke and
Foerster (1915) and Betts (1916). The most graphic desc.ription was given by Church who described the. ideal forest for
snow accumulation as resembling a giant honeycomb, the
glades of the forest repre.senting the c.ells of the comb.
l\filler (1964 and 1966) presented two comprehensive.
reviews of interception processes and transport of intercepted
snow during snowstorms. In these reviews Miller discussed the
factors influencing the adhesion of snow on foliage temperature., wind and characteristics of the obstades; and the factors
influencing cohesion of snow atmospheric a.nd crown conditions. Processes involved in transport of intercepted snow
from tress induded snow sliding from branches, stem flow and
dripping of melt water, vapor transport from melt water and
1Associate Vice President for Research and Professor of Watershed
Management, Colorado State University, Fort Collins, Colorado 80523.
61
before and after thinning indicated a peak snow water equivalent increase of 2 inches or approximately 30 percent.
extension was done on the lee side of the original cut. Data for
10 winters indicated an average net loss of 6.5 percent for all
widths when the volume of snow in the opening plus that in the
lee forest was compared with the upwind forest even though
there was 20 to 48 percent greater snow accumulation in the
openings. Sublimation and wind transport outside the. plot (i.e.
into the lee forest beyond the measured area) were thought
to
.
account for the loss. For two of the ten years, barners were
constructed along the lee side of the 3H opening. For the 1974
snow year a belt of small (5-1/4-foot) lodgepole trees was
erected along the lee border of the cut area. For the 1978
winter a 12-1/2-foot wood sno~r fence (40 to 50 percent
density) was used. Placement of the barriers did not change the
expected pattern of snow accumulation inside the clearing but
snow catch along the lee side of the clearing and lee forest
border was greatly altered. The fence. was more effective than
the trees and resulted in a 13 percent net snow increase on the
study plot (opening plus lee fore.st). The. barriers provided
evidence that considerable amounts of snow are transported
away from the lee forest border.. by wind action.
A set of studies in Canada (Golding and Swanson, 1986)
have particular relevance to Fraser studies. At the James River
study area, 60 miles northwest of Calgary, Alberta, the authors
reported a spatially preferential loss from the snowpac.k in
different sectors within forest dearings. The implication from
this study is that differential ablation during the accumulation
period can be an important factor in evaluating differences in
snowpac.k accumulation in forest openings. At the James
River study site snow water e.quivalent in 1/4H to 6H circular
clearings range.d from 13 to 45 perce.nt greater than in the
forest and was reported to be "probably" a result of a
combination of interception and redistribution.
At the l\larmot Creek experimental watershed 24 miles SE
of Banff, Alberta, clearings on two subbasin clearings were
studie.d Twin and Cabin. On the. Twin subbasin, clearings of 3/
4 to 1-1/4H had 28 percent greater snow water equivalent than
the intervening forest which the authors reported "seemed" to
be the re.sult of redistribution because the increase in the
clearings just balances the decrease in the forest (based on an
calibration with separate control area). On the Cabin subbasin
the. 20 to 32 acre blocks averaged 20 percent greater snow
water equivalent than the forest and there was no evidence of
redistribution of snow. The authors suggest that the increase
is the result of elimination of interception.
These studies illustrate the complexity and frustration of
trying to separate the interception redistribution ablation
effects on snow accumulation and, as the authors indicate, ".
.. the data do not provide definitive answers c.oncerning the
source of increased snow water equivalent in forest clearings."
Gary and Watkins (1985) reported on the effects of
thinning a lodgepole pine stand in "'yoming at an elevation of
9000 feet. The thinned area had a lodgepole stand of 10,000
stems/acre before thinning and was thinned to a density of
about 850 trees/acre with a basal area of 70 ft2/acre. The
remaining trees had an average diameter of 4 inches and an
average height of 30 feet. Comparison with a control area
Fraser Studies
.
Wilm and Dunford (1948) reported the first comprehen··
sive snow accumulation studies at Fraser. Twenty harvest
cutting plots were established in 1938. The five acre plots were
in mature lodgepole pine (Pinus contorta) intermixed with
Engelmann spruce (Picea engelmannii) and alpine fir (Abies
lasiocarpa). The stand contained 300 to 400 trees per acre
larger than 3-1/2 incbes d.b.h. with a height range for most of
these trees between 35 and 85 feet. The merchantable timber
volume (trees larger than 9-1/2 inches d.b.h.) averaged 12,000
board feet per acre. These stands were at an elevation of 9150
to 9700 feet. The experiment was designed to place four
treated and one control plot in each of four randomize.d
blocks. In 1940 all trees larger than 9-1/2 inches d.b.h. were
removed from one plot in each block; three other plots were
cut to a residual stand of 2000, 4000 and 6000 board feet of
merchantable volume per acre.
In order to determine the effects of timber cutting on snow
storage, 25 sampling points were established in each plot.
Snow water equivalent was measured with a Utah snow
sampler and weighed with a balance to 0.1 ounce between
March 15 and April 1. These measurements were taken in 1938
and 1939 before cutting and in 1941 to 1943 after cutting in
1940.
The after harve.st value.s as adjusted by "Tilm and Dunford
are presented in table 1. These values were calc.ulated by
covariance analysis used to adjust for aspect and yearly
snowfall differences. Thus the heaviest cutting resulted in a net
gain of 1.99 inches or 26 percent over the uncut plots. Snow
accumulation increased in relation to intensity of cut. In
presenting these results on snow accumulation, the investigators wrote as follows:
The smallest quantities were observed under dumps
of trees, and the largest quantities in the largest
available canopy openings, about 60 feet in diameter.
These observations provide a graphic clue to the
probable effect of timber cutting on snow storage,
because such treatments would increase the number
and size of openings in the forest, and hence it should
increase the average amount of stored snow.
Another important finding came from these early studies.
On one half of each cut plot a minor timber stand improvement
Table 1.--lnltlal snow storage as a "esult of timber cutting (Wllm
and Dunford 1948).
Treatment
11,900 f.b.m. uncut
6,000 f.b.rn. residual stand
4,000 f.b.rn. residual stand
2,000 f.b.rn. residual stand
o f.b.m. residual stand
82
Inches of water
7.(50
8.41
8.61
9.09
9.59
---
was made. by removing undesirable trees within the diameter
range from 3.6 through 9.5 inches. The number of trees
removed averaged 56 per acre. This treatment resulted in an
average increase of 0.46 inches in snow accumulation or about
a 5 percent gain.
In addition to comparing the initial snow storage (Le.
snowpack accumulation as of March 15 April 1), a comparison
was made of net spring precipitation (mostly snow) during the
period from March 15 A prill to June 30 by using nonrecording
rain gages on each of the plots for the years 1941 to 1943. These
results from Wilm and Dunford are presented in table 2. Wilm
and Dunford made severa.l sali~.nt observations on the spring
period results pointing out that about four fifths as much water
was supplie.d by this source as by stored winter snow, and that
the percentage increases resufting from heavy cutting were
very similar to those found for winter snow storage.
Although 'VHm and Dunford did not specifically mention
the cause of the increased snow accumulation in their original
work, later interpretation by Goodell and Wilm (1955) attribute.d it to the eljmination of evaporation losses from snow
jntercepted on tree crowns.
Hoover and Leaf (1966) summarized much of their observations on snow interception at Fraser. Based on photographic
records during the 1963 and 1964 snow season and long term
nleasurements on Fool Cree.k, they inferred that snow re.distribution could be a major factor causing differential snow
deposition. This inference was based on their observations
that snow remained on trees a relatively short time at their
observation site near the Fraser Experimental Station headquarters, that the analysis at that time. indicated no overall
increased snow accumulation on the Fool Creek Watershed as
a result of cutting, and that, despite considerable regrowth of
young trees on the clear cut and heavily thinned plots of Wilm
and Dunford, the ratio of treated to uncut plots had changed
little if any. In concluding, the authors emphasize.d the extreme.Iy complex series of proce·sses re.Iated to the accumulation and disposition of intercepted snow and called for additional studies on the aerodynamic processes involving transport of snow through and from the forest canopy.
1943. These watersheds were calibrated from 1943 to 1952.
Roads were constructed on Fool Creek in 1952 and timber was
harvested in 19541956. Forty percent of the 714 acre watershed was cut in alternating strips with uncut forest of 1 to 6 tree
heights wide (66 to 396 feet). Snow water equivalent was
sampled at approximately 100 points on each watershed on or
about April 1 from 1943 to 1954 prior to cutting on Fool Creek.
Postharvest measurements at the same points were reported
for 1959 and from 1967 to 1984. Intensive measure.ments we·re
made to compare the cut and uncut strips in 1964 and 1979.
The observed peak snow water equivalents on Fool Creek
and East St Louis Creek along with the estimated increase on
Fool Creek are presented in table 3. This analysis indicates a
1.0 inch (9 percent) watershed wide inc.rease in snowpack
water equivalent as a result of the timber harvest on Fool
Creek. This is the first reported analysis to indicate an increase
in snowpack on the overall watershed. If all of this 1.0 inch
increase occurred on the 40 percent cut area, then the average
increase on the cut area. would be 2.7 inches. This appears well
within the 3.4 inches (23 percent) increase reported by Leaf
(1975) in c.omparing the cut and uncut strips on Fool Creek. An
additional set of measurements were made on selected strips
to check the cut versus uncut snow in 1979. The average
increase on the cut strips was 3.8 inches (28 percent).
The exact proce.sse·s responsible for the increased snow in
cut areas are still not clear. Recent work at the Fraser
Experimental Forest by Troendle and l\leiman (1984) using
snowboards in small openings (1.5H) and in the adjacent
forests confirmed the increases in the openings, but did not
support the concept that snow was redistributed from the
forest into the openings during the intervals between storms.
Furthe.rmore, the percentage increase indicated by snowTable 3.~-Comparlson of snowl,ack peak water equivalents (Inches of
water) on Fool Creek and East St Louis Creek Watersheds
(Troendle and King 1985).
Fool Creek
Est. Incr. Fool Creek1
Year
East Sl Louis
1959
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
Average
Clearcut Studies
The Fool Creek watershed has been an important source
of information on snow accumulation. This data was summarized most recently by Troendle and King (1985). The Fool
Creek gage was constructed in 1941; the East St Louis gage in
Table 2.--Net precipitation during spring snowmelt period as a
result of cutting (Wllm and Dunford 1948).
Treatrnent
11,900 f.b.m. uncut
6,000 f.b.m. residual stand
4,000 f.b.m. residual stand
2,000 f.b.m. residual stand.
f.b.m. residual stand
o
Inches of water
5.73
6.60
7.01
6.94
7.56
12.1
9.6
11.3
10.0
8.0
16.3
10.6
7.8
12.7
9.8
9.2
5.8
12.8
11.4
13.9
5.4
15.8
12.2
12.7
12.0
19.0
20.1
15.3
11.4
15.6
12.5
12.9
8.1
15.9
15.6
18.4
7.8
1.6
0.8
·-0.6
0.2
0.4
1.1
2.8
2.1
0.7
0.9
0.9
1.1
0.9
2.2
2.1
1.3
12.6
15.1
15.6
17.2
0.8
·-0.5
1.0
1Estimated as PWE == PWE (Fool Creek) (0.37 + 1.146PWE East St
Louis),R2 = 0.93, standard error == 1.0inches; where PWE = peak water
equivalent.
63
tion occurred. The average accumulation on all boards in the
open was 104 inches of snow (de.pth, not water) compared to
68 inches in the forest giving a 65 percent increase. Virtually
all of the increased accumulation occurred during, not after
snowfall events. There was no diffe.rence betwe.en upwind and
downwind forest plots. These results confirmed the earlier
re.sults (Troendle and l\leiman, 1984) obtained on three openings 1.5H in diameter.
The most recently completed study at Fraser of snow
accumulation is that of Wheeler (1987). He used the same
plots as were used by Troendle and Meiman (1986), but greatly
increased the number of events sampled and the sampling
intensity. Each snowboard sample was weighed to determine
actual water equivalent on the snowboard. In addition to the
snowboard measurements, a recording anemometer was installed on a tower at 70 feet above. the ground in the c~e.nter of
the de.arcut plot. During the pe.riod from January to April,
1986, 22 snowfall events and 21 inter storm inten'als were
observed. Redistribution from the forest to the dearing was
observed only one time and accounted for only one percent of
the difference in accumulation in the clearing.
board measurements were larger than those found by snowpack water equivalent comparisons, thus indicating a relatively greater vapor loss from the snowpac.k in the openings.
The data for 'the 18 events measured in January through
l\iarch, 1984 are pre.sented in table 4. The ave·rage increase in
the opening compared to the windward forest was 31 percent.
In only one of the plots was there a significant difference in the
downwind plot. Very little redistribution occurred between
the 18 snow events. The accumulated amount of snow measured in the openings averaged 133 inches, approximately 0.8
inches or less than 1 perc.ent was measured in the between
snowfall intervals.
In order to measure more carefully the water balanc.e
effects of patch clearcutting, a plot study was established on
a 35 percent north facing slope' at the Fraser Experimental
Forest at an elevation of 9200 feet. The site was a uniform
forest of Engelmann spruce, SUbalpine fir and lodgepole pine
with an average canopy height of 64 feet. In 1980 the site was
divided into three equal plots 260 feet wide and 400 feet long.
In the summer of 1982 the centae plot was dearcut after two
years of calibration measurements of snow water equivalent
and soil water content. Comparison of peak snow water
equivalent for five years are presented in table 5. The increased accumulation averaged 5.8 inches of water or 45
percent more than in the upwind plot (probability < 0.001).
Furthermore, the.re was no significant difference in the downwjnd forest plot.
Twelve snowboards were place.d on each plot and read at
20 differe.nt times during the period betwe.en .lanuary 2, 1985
and April 4, 1985. The boards were read after each storm and
during nonstorm periods to determine when storm redistribu-
Snow accumulation in the upwind and downwind forest
was compared for seven storms. None of the storms showed
a significant decrease in the mean snow water eql;1ivalent in the
downwind forest. A comparison of the dearing with the
upwind forest indic.ate·d a 31 perc.ent greater accumulation in
the. clearing for the 21 storms. An analysis of average wind
speed during the storm as related to the perce.ntage increase
in the elearing resulted in a strong negative correlation r = 0.74
(p = 0.002). The inference drawn from the. lack of downwind
effect and the negative corre.lation of snow increase in the
opening with increase in windspeed was that snow interception was the dominant process influencing increased snow
accumulation in the dearing.
The recommendations from earlier studies that a watershed be treated with 5H circular openings was implemented in
the North Fork of Deadhorse Creek in 1977. Timber was
removed on 36 percent of the area by commercially elearcutting 12 small units approximately 5H (400 feet) in diameter. All
slash was lopped to a 4 inches top and scattered. Comparative
snow course observations betwee.n Deadhorse and East St
Louis Creek began in 1967. Transects consisting of a total of
118 sampling points cross all major slopes, aspects and elevations on Deadhorse. Snow sample.s using a federal snow
sampler are taken about April 1 each year.
Table IJ.--Comparlson of snow accumulation (Inches) In the forest and
open averaged for 18 snow events and COml)arlson of I)eak
SnOWI)ack water equivalent (percent) on AI>r1l1.
Unit
1
2
3
Windward
forest
5.7
4.S
4.5
Open
7.4*
5.9*
5.9*
%Inleeward crease In
open
forest
4.8""
4.1
4.3
% Increase
In snow water In open,
AI>r1l1.1
30.3
31.6
31.6
26
16
16
""Significantly different from windward forest at P = O.OS.
1Federal snow sampler measurements.
Table 5.--Peak snow water equivalent (Inches) as a result of timber
cutting (Troendle and Melman 1986).
Year
Upwind plot
1981
1982
6.1
12.2
1983
1984
1985
11.9
14.8
11.8
Cut plot
Covariance analysis of the pre and post treatment data
indicated no overall change in snowpack water equivalent on
Deadhorse North Fork \\'atershed following timber cutting
(Troendle and King, 1987). The authors attributed this lack of
difference in snow accumulation to the offsetting influence of
greater snow ablation in the openings on this south facing
watershed. Intensive sampling of several of the openings and
the surrounding forest in 1981 indicated an 18 percent greater
accumulation in the openings. Be·cause of the potential confouncUng of differential ablation with accumulation processes,
Downwind plot
------
6.2
6.1
12.5
12.S
--•.•••• Center plot cut ....... .
17.2*
12.3
14.4
21.3*
17.S*
Missing
""Significantly different from upwind plot (p < 0.001).
64
it is not possible to separate interception and differential
deposition processes in this data.
One final study dese.rves mention in relati.on to dearcutting. The optimum size of elearcuts generally has be.en given
as approximately 5H (Troendle, 1983) with the assumption
tha.t larger openings are subject to wind scour. A study was
initiated in 1981 to see if larger openings would hold more
snow than the adjacent forest if sufficient roughness were
maintained in the form of slash and non commercial trees
(Troendle and Meiman, 1984).
In 1981 an 20 acre area surrounding one of the original 8
acre c1earcut plots studied by,\\!ilm and Dunford was dearcut
along with the original 8 acre area. All merchantable trees
were removed, the slash lopped and scattered and most of the
larger trees felled. About 4 to 6 cavity trees per acre as well as
the non commercial ste·ms less than 6 inches d.b.h. were left
standing.
In the summer of 1983, all remaining trees on the site were
felled. A layer of slash up to 24 inches high remains. Peak
snowpack wa.ter equivalent measured around April 1 in 1982
and 1983 after the original 8 acre plot (5 acre cut + 3 acre
boundary) was recut produced no scour in the original 8 acre
area as a result of the now 28 acre opening. This indicated there
was still enough roughness in the slash and remaining trees to
protect the area from scour. After the removal of all remaining
trees in 1983, the accumulation patterns were as presented in
figure 1. These results suggest that the. slash is still an effective
snow trap in the large opening, but once the snowpack reaches
the level of the slash then effectiveness decreases.
have been somewhat overshadowed by the Fool Creek cutting
and the emphasis on small dearcuts as the preferred water
yield management practice.
Hoover and Leaf (1966) presented data on follow up
measurements on the original,\\Tilm and Dunford plots. Their
measurements for 1956 and 1964 have been added to the
original data and are presented together as table 6. In presenting the remeasured plot data, Hoover and Leaf emphasized
that the relative snow storage amounts had changed little if any
between 1941 and 1964 in spite of the considerable regrowth
of young trees and increased canopy density on the more
heavily cut plots. They attributed the effect on the 0 and 2,000
f.b.m. plots to the I trapping of snow from surrounding old
growth trees, but pointed out that a longer regrowth period
was needed for more conclusive results. It is of interest to note
that the 6,000 and 4,000 f.b.m. thinning effects persist as well
as those on the more heavily cut plots.
Troendle and Meiman (1984) analyzed records for one of
the original ,\\Tilm and Dunford dearcut plots for the period
1941 through 1981. This analysis indicated that the increased
snow accumulation in the dearcut area has been diminishing
by 0.028 jnches per year since 1941. In the· 40 year period the
recovery was 1.14 inches of the original 2.95 inches differe.nce.
Using a linear fit, total recovery would take 103 years. However if the nonlinear growth curve is assumed, total recovery
could be expected in a shorter period of time.
Peak snow water equi.valent has been measured on four
different stand densities in lodgepole. pine beginni.ng in 1978.
Each trunning level is applie.d to a 0.5 acre site and replicated
five times. These data are presented in table 7 and have been
reporte.d in part in Gary and Troendle (1982) and Troendle
Thinning Studies
Table 6.--Snow storage on lodgepole pine harvest plots.
Beginning with the work of Wilm and Dunford a number
of studies have been conducted at Fraser over the years on the
effects of partial cutting on snow accumulation. These studies
Merchantable
reserve stand per
acre
(f.b.m.)
140
0'
0
130
x
11,900, uncut
6,000
4,000
2,000
~85
Before treatment
1938-9 1
1941-3 1
---------- (Inches of water) ---------7.0
8.0
8.7
9.7
9.7
6.5
6.8
6.9
7.0
6.8
o
After treatment
19562
19642
8.4
10.8
11.6
4.8
5.6
6.3
6.8
6.7
u;
OJ
.2
120
:s:
(J)
~
c
110
OJ
c.
0
w
:s:
1From Wilm and Dunford 1948, unadjusted data.
2From Hoover and Leaf 1966.
~
w
1984
Table 7.--Maxhnum snowpack wstel' equivalent (inches) as related to
basal area (ft2 per aCl'e).
100
(J)
90
4
6
8
10
12
14
16
Year
140
19713
9.9
8.7
10.5
197!~
18
1980
19131
1982
198:3
19137
Snow water equivalent (SWE) in forest (inches)
Figure 1.--Comparlson of snow water equivalent In open to forest as
season progresses.
65
8.3
9.1
6.0
---------- Basal
120
9.1
13.9
11.2
3.:3
8.3
9 .:>
'5.8
area ----------
80
40
9.6
9.8
11.6
3.5
8.9
10.2
10.4
12.1
3.9
8.9
10.1
6.4
9.5
6.4
and ~feiman (1984). There is a consistent significant difference (p = 0.05) between the 40 and 140 levels. Although there
is a general trend of increased snow water equivalent with
de.creased basal area at the intermediate levels, these are not
statistically significant.
A much larger scale thinning study was established on
Unit 8 of Deadhorse Creek Unit 8 is a 100 acre north facing
slope that was partially cut in 1980 in the first step of a three
step shelterwood cut. Approximately 40 percent of the basal
area was removed as individually marked trees 7 inches d.b.h.
and larger. Peak snowpack water equivalent on Unit 8 was
compared to that on the East St Louis Creek control for 14
years prior to thinning and four years after. The r value for the
pretreatment correlation was 0.9~ with a standard error of 0.2
inches. Peak water equivalent compared to the control increased 1.9 inches or 16 percent over the entire unit (Troendle
and King, 1987). The re.suIts from this study indicate that the
thinning effects found on plot studies also apply to larger
thinned areas and, the.refore, strongly suggest that the proce.ss
4
responsible. is interception.
Troendle (1987) in attempting to summarize data on
thinning and dear cutting at Fraser and related studies developed the relationship presented in figure 2 illustrating the
general relationship between basal are·a and snow accumulation.
treated areas. The increase on Fool Creek in the cut areas
appears to be approximate.ly 23 percent and on the North Fork
of Deadhorse Creek approximately 18 percent. Conside.ring
the entire watershe·d including cut and uncut are.as, the·re is an
overall 9 percent increase on Fool Creek and no increase on
North Fork of Deadhorse Creek. These effects of clear cutting
small areas appear to be long lived, at le.ast we.11 be.yond the
almost 50 years of records to date. There is also some evidence
that we can achieve snow accumulation increases on cut areas
larger than 5H if we pay attention to maintaining sufficient
surface roughness through slash disposal and residual trees.
Inc.reases from thiJllning are somewhat more variable, but
information to date indicates increases from 10 to 25 percent
for basal area reductions of from 40 to 80 perce.nt respectively.
Demands on forest managers can change over time therefore the best knowledge base for sound management is a
thorough understanding of processes responsible for changes
brought about by different management practices. The effects
from both thinning and dearcutting have been demonstrated
on watershed as well as on plot studies. However a thorough
understanding of the processe·s responsible is not yet in hand.
The longer data base now available indicates a 9 percent net
increase of snow on the overall watershed on FOQI Creek thus
suggesting interception savings are important. We have not
found significant redistribution of snow from forest to openings during the intervals between storms. Still inseparable are
the processes of inte.rception and differential deposition
during snowfall events. Hopefully the snowfall process studies
using snow partide counters now underway at Fraser will help
us define better what is happening during snowfall events. We
have. not found consiste.nt decreases of snow acc.umulation in
forests downwind from openings. In those instances where
such decreases have been observed, it is not clear to what
extent wind scour has moved snow deeper into the fore.st.
There is also evidence that differential ablation in the open
areas and adjacent forest borders is a more important factor
in the subalpine than previously thought.
Summary and Management Implications
Fifty years of studies at Fraser have given us a wealth of
information on the influence of forests on snow accumulation.
There is ample evidence that both clear cutting and thinning
produce significant increases in snow accumulation on the
lC Wilm & Dunford 1948
• Troendle & Meiman 1984
o Troendle 1983b
£. Gary & Troendle 1982
... Gary & Watkins 1985
D Troendle & Meiman 1986
50
c
D
Q)
'i
>
·s
40
C'
I: ~ ~. . . . . ~.~. . . ~.... .
Qj
•
ro
.•.••
c
••••••
.. .
Q)
u
Qj
All of the above reinforce the need to continue the process
studies together with the larger area watershed measurements. It is this combination of integrated process, plot and
watershed studies that has made Fraser such a valuable source
of information for land managers through these past 50 years.
o Fool Creek
• Deadhorse Creek
Q)
10
y= 34.3 - .038x
R=.85
SE=7.7%
References
£.
Betts, N. DeW., 1916. Notes on forest cover anti snow retention on the east slope of the Front Range in Colorado.
Proceedings Society of American Foresters, 11:27-32.
Carpente.r, L.G., 1901. Fore.sts and snow. Colora.do Agricultural Experiment Station Bulletin 55.
Church, J.E., 1912. The conservation of snow: its dependence
on forests and mountains. Scientific American Supplement 74:152-155.
~
...........................
c..
100
80
60
40
20
o
Percent basal area removed
Figure 2.--Summary of cutting experiments at Fraser (l'I'oendle 1987).
66
H.'' .
Gary, Howard L. and Ross K. Watkins, 1985. Snowpack
accumulation before and after thinning a dog hair stand
of lodge.pole pine. Rese.arch Note Rl\f 450. U.S. Department of Agriculture, Forest Service, Rocky l\fountain
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Gary, Howard L. and Charles A. Troendle, 1982. Snow
accumulation and melt under various stand densities in
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Service Re.search Note. RM 417.7 p.
Gary, Howard L., 1980. Patch dearcuts to manage snow in
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Gary, Howard L., 1974. Snow accumulation and snowmelt as
influenced by a small dearing in a lodgepole. pine forest.
Water Resources Research 10(2):348-353.
Goodell, B.C. and H.G. Wilm, 1955. How to get more snow
water from forest lands. U.~. De.partment of Agriculture
Yearbook, 1955. 228-234. •
Hoover, l\fan'in D. and Charles F. Leaf, 1966. Process and
significance of interception in Colorado subalpine forest.
In: International Sym posium on Forest Hydrology. Pergamon }'ress. pp 213-224.
Jaenicke, A.J. and M.H. Foerster, 1915. The influence of a
western yellow pine forest on the accumulati.on and
melting of snow. Monthly V\'eather Review. 43:115-126.
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Hilgardia 22(1).
Leaf, Charles F., 1975. Watershed management in the Rocky
l\fountain subalpine zone: the status of our knowledge.
USDA Forest Service Research Paper RM 137. 31 p.
Lull,
and F.l\I. Rushmore, 1960. Snow accumulation and
melt under certain forest conditions in the. Adirondacks.
U.S. Forest Service, Northeastern Forest Experime.nt
Station Paper 138.
Meiman, J.R., 1970. Snow accumulation related to elevation,
aspect and forest canopy. In: Snow Hydrology, Proceeding of V\Torkshop Se.minar, 1968. Queens Printer for
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maximum snowpack water equivalent in a western white
pine forest. Forest Science. 8:225235.
Troendle, C.A., 1983. The potential for water yield augmentation from forest management in the Rocky Mountain
Region. Water Resources Bulletin 19(3):359-373.
Troendle, C.A. and R.l\f. King, 1987. The effect of partial and
c1earcutting on streamflow at Deadhorse Creek, Colorado. Journal of Hydrology 90:145157.
Troendle, C.A. and R.M. King, 1985. The effect of timber
harvest on the Fool Creek watershed, 30 years later. Water
Resources Research. 21(12):19151922.Troendle, C.A.
and J.R. Meiman, 1986. The effects of patch dear cutting
on the water balance of a subalpine forest slope. In:
Proceedings of 54th V\'estern Snow Conference. 93-100.
Troendle, C.A. and J .R.l\feiman, 1984. Options for harvesting
timber to control snowpack accumulation. In: Proceedjngs of 52nd Western Snow Conference. 86-97.
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67