WSP00036

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/1/1975
• Author: BOR
• Title: San Juan Ecology Project - Interim Progress Report - March 1975
• Water Supply Pro - Doc Type: Report/Study

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(Fig. 1). These data indicate that bolewood produc-
tion on a yearly basis was not significantly influ-
enced by varying environmental factors, including
those influenced by changes in snow parameters. It
has been suggested that cambial activation may begin
with snow still on the ground. Sometimes, this snow
persists for some time into the growing season (Fig.
4). If this persistent snow influences cambial cell
division and expansion early in the growing season,
this delay in growth may be compensated for by more
rapid growth later in the season, resulting in a
comparable amount of wood produced each year. In
another study with Engelmann spruce Gary (1974) found
that the growing season was long enough to overcome
any inhibitive effect due to late-lying snow and that
there was no significant difference in growth between
snow-covered and snow-free plots. This type of
"catch-up factor" has also been suggested for other
subalpine plant species (Owen, 1973).

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This constant annual wood production can probably be
ascribed to the intrinsic genetic controls of the
species themselves. These spruce and fir trees have
genetically adapted over long periods of ecologic
time to the environmental conditions of the subalpine
and thus, the amount of wood produced each year
appears to be fixed.

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4.4.3. Conclusions and Recommendations

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Individual trees of the Engelmann spruce-subalpine
fir association were shown to exhibit relatively
constant bo1ewood production on a yearly basis. This
constant production is attributed to, the genetic
properties of the species themselves, rather than
controlled by factors of the environment. Therefore,
changes in snow parameters probably do not affect the
wood production of individual spruce trees on a year
to year basis.

Bolewood production of spruce-fir stands was also
shown to remain constant over the 20 year study
period. This trend is probably a function of genetic
control also, because stand production is a reflection
of the cumulative responses of the individual trees.
Such constant production is also a result of the
climax status of these forests; uneven-aged climax
forests typically exhibit a constant production over
time with minor fluctuations resulting from individual
tree mortality.

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Bole biomass values for these stands were shown to
exhibit severe perturbations in standing crop values
and these sudden losses in biomass were attributed
to catastrophic events such as windthrow, insect out-
break or fire. Therefore, these forests could be
chara~terized as a "disturbance climax" in which the
spruce and fir trees dominate the site and reproduce
under their own shade, but show severe fluctuations
in standing crop because of disturbance events. It
is debatable as to whether changes in snowpsck
conditions could positively or negatively influence
these disturbance events.

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These conclusions must be conditional, however, due to
the short time period of this study. Cumulative
effects of snow manipulation could not be evidenced
in a study of this duration and detrimental effects of
direct snow on sapling and seedlings could affect the
future status of these forests. Therefore, it is
recommended that future studies be conducted on seed-
ling establishment and early growth. Also, the cell
deposition pattern within the growing sesson should be
investigated to reveal possible delayed cambial
activity in years of late sn~ melt.

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4.4.4. Literature Cited

Alexander, R.R. 1958. Silvical characteristics of
Engelmann spruce. USDA, USFS, RMFRES Sta.
Paper 31. 20p.

Blaue, R.W. 1973. Phenology of Engelmann spruce
in southwestern Colorado. M.S. Thesis, Colorado
State University, Ft. Collins, Colo. 85 p.

Gary, H.L. 1974. Growth of Engelmann spruce (Picea
en~elmanni1) unaffected by increased snowpack.
Arctic and Alpine Res. 6:29-36.

Kirs, T., H. Ogawa, K. Yoda and K. Ogino. 1967.
Comparative ecological studies on three main types
of forest vegetation in Thailand IV. Dry matter
production with special reference to the Khao
Chong rain forest. Nature and Life in Southeast
Asia 5:149-174.

Ovington, J.D. 1962.
woodland ecosystems
Res. I:103-183.

Quantative ecology and the
approach. Adv. in Ecol.

Owen, H. 1973.
The San Juan
Report 1973.
7052-Z.

Herbaceous phena10gy p. 14-16 IN:
Ecology Project, Interim Progress
U.S. Bureau of Reclamation, CSU-DWS

Whittaker, R.H. 1970. Communities snd ecosystems.
Collier-Macmillan Ltd., London. l58p.

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