WSP09641

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/9/1976
• Author: Steinhoff and Ives
• Title: Ecological Impacts of Snowpack Augmentation in the San Juan Mountains - Colorado - March 9 1976
• Water Supply Pro - Doc Type: Report/Study

1- Report No. OD225S 2. 3. Recipient's Accession No.
CSU-FNR-7052-1
4. Tit Ie 5. Report Da te
Ecological Impacts 'of ~owp8ck Augmentation in the San Juan March 1976
Mountains of Colci~rado . 6. ,
"
7. Author:(s) 8. Performing Organization Report No. ;
" ,
Harold W. Steinhoff and Jack D. IveB (EdB)
9. Performing Organization Name and Address O. Work Unit No. ,
College of Forestry and Natural Resources
Color"a.do State. Univers.ity l- Contract or Grant No.
Fort Colltns, Colorado 80523 14-06-D-7052
2. Sponsor tng .Agency Name and Address 3. Type of Report
Bureau of Reclamation Final Report
Building 67, Denver Federal Center 4.
Denver, Colorado 80225
5. Supplementary Notes
This document represents a cooperative research effort between Colorado State University, the University of
Colorado. Bnd Fort Lewis College. This report supersedes the previous Interim Progress Reports of 1971 ,
1973, Bnd 1975. Also, this report has been designated as a contribution to the United Nations Man and the
Biosphere (MAB-6) Program.
6. Abstract
The following conclusions summarize the work of 33 scientists from Colorado State UnIversity, the University
of Colorado, and Fort Lewis College who studied the effects of varying snowpack on the ecosystems of the San
Juan Mountains in Colorado from 1970 to 1975. Initiation of ahoot elongatIon was delayed for plallts 1n the
tundra and forests as a re8~lt of lower temperatures associated with deeper snowpack. The delay was most ap-
parent for herbaceous species, such as Thurber fese ue (festuca thurberi), whose growth points lay in the
immediate zone of lower temperature at ground level. The effect on trees such as Engelmann spruce (Picea
en~elmanii) and quaking aspen (Populus tremuloides) was less. The result was a decrease In hiomass production
of herbaceous species. but not of trees or of Gambel oak (Quercus ~ambellli). which was found in a zone that
became snow clear very early. The delay in beginning of growth persisted through the other stages of the
annual cycles of most plants but with less magnitude. There seemed universally a compensation factor which
permitted each species to compress ita annual cycle in years with a ahorter growing season caused by greater
depth of snowpack. Phytosoclological studies in both foreats and tundra showed that plant communities wer~
arranged along a snow clear date gradient. In the forest, Gambel oak gives way to quaking aspen. then to sub-
alpine fir (Abies lasiocarpa), and finally to Engelmann spruce, BB the snow clear date extends later into
the year. A noticeable decline in forest populations of deer mice (Peromyscus maniculatus) and. to a lesser
extent, chipmunks (Eutaudas spp.) and Microtus spp., followed winters of heavy snowfall. The basic reason
was a delRY in breedjng and in availability of essential foods. No similar effect was found for the pot':: ki:! t
gopher (Thomomys talpoides) or mountain toad (Bufo~). Elk (Cervus canadensis) were almost excluded
from regions with more than 70 cm of penetrable snow depth, and their travel was noticeably restricted at
depths over 40 em. Movement of elk to higher elevations in spring coincided with the initiation of gro.....th of
herbaceous plants rather than directly with the receding snow line, and adequate calving aress were always
present. Plant litter in the tundra decreased in areas df deeper snowpack. Local changes 1n the rate (If
50il erosion may increase by a factor of 10 a9 a result of the greater area of bare 90il left by thp. decrertAt>
in vegetative, cover around snowbanks. The area involved is small and thus the total impact is very small
regionally. The long term climatic trend since 1930 has been toward higher temperatures and les8 precipitatioll,
with short term fluctuations, of a few years, from relatively dry to wet modes. No significant loc reases 'n
silver concentration were detected, because of the small amounts added in cloud seeding and the high back-
ground levels of silver in the target area. No deleterious effects of silver iodide have been found at con-
centrations which could be expected due to cloud seeding.
17. Key Words 18. Distribution Statement
alp ioe tundra , climate, cloud seeding. Colorado, Available From:
aspen, National Technical Information Service
ecology . ecosystems , elk. environmental impact, fescue, Springfield, Virginia 22151
fo~eBt5. geoworphology. oak. phenology, phytosociology.
productivity, San Juan Mountains. silver iodide, small
mammals, snow, spruce, weather modification.
19. Secuirty Clasaif. of this report 20. Secur1ty Classif. of this page 2l- No. of pages 22. Price
Unclassified Unclassified 489

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