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

mate!y the same ttme every year, significant prob-
lems could arise if the high stress period was
extended late enough into the summer period by
increased snowpack. These phenologic events current-
ly oocur after the period of high water stress. If
they occurred during the period of high stress. a
significant growth reduction might occur. Further
coordination with the Tree Biomass and Tree Phenology
projects will be necessary to examine these implica-
tions.

4.5.4. Proposed Future Research

Little additional field data will be collected during
the upcoming year except to fill some gaps of missi~
information. The majority of effort.will be concen-
trated on computer analysis of data for all six
plots and analysis and interpretation of the root
resistance study. When the tree core information
becomes available, it will be correlated with
moisture stress.

4.5.5 SummarY

The growlng,season of Engelmann spruce can be divided
into two parts concerning water s.ress, the snowmelt
period and the midsummer peribd. Water stress
during the midsummer period is primarily determined
by daily weather and expressed as two factors, one
atmospheric and the other deep soil. A regression
model was developed to predict water stress during
this period from the following variables (R2 - .81);
surface soil temperature, air temperature, -25 soil
temperature. and -15. cm soil water.

The snowmelt period is characterized by high levels
of ~idday water stress which become less severe as
snowmelt prQceeds and more soil is bared -of snow.
The 50% reduction in midday stress over this period
1s probably due to lowered root resistance to water
flow c8used'by increasing soil temperatures. This
theory is substantiated by preliminary analysis of
root resistance studies which demonstrated a rate of
water movement through roots at 7.5oC about 3X
greater than at O. SoC. ~

The major effect of these high stress levels during
snowmelt would be in photosynthesis reduction rather
than cell division since trees were able to rehydrate
at night. ~s long as this high stress period occurs
before the beginning of major phenological activity,
little change in growth would be expected. If
delayed snowmelt from snowpack augmentations resulted
in the high stress period being extended later into
the year, occurrence of phenological events during
this stress period could result in a significant
alteration ~f growth pattern.

4.5.6. Literature Cited

Evans, A.K. 1973. Patterns of water stress in
Engelmann spruce. M.S. Thesis. Colorado State
University. 57 pp.

A cold tempera-
technique.

Evans, A.K. and C.P.P. Reid. 1974.
ture error in the pressure chamber
Can. J. Forest Res. (In press).

Reid, C.P.P. and A.K. Evans. 1971. Moisture stress
as an indicator of the effects of snow on biomass
product~on of forest trees, pp. 58-78. ~ An
evaluat~on of the ecological impact of weather
modification in the Upper Colorado River Basin.
Teller, H.L., J.D. Ives, and H.W. Steinhoff (eds).
CSU-DWS :Report No. 7052.

Reid, C.P.P. and Kent Evans. 1973. Moisture stress
as an indicator of the ef ects of snow on biomass
,production of forest tree pp. 34-39. In
Teller, H.L., J.D. lves, nd H.W. Steinhoff (eds).
CSU-DWS Report No. 7052-Z

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