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j; :" " ,. ,. 001569 f CSU-OWS-7052-3 I 2. Government Accession No, 3. Recipient's Catalog No. 5. Report Date The San Juan Ecology Project March 1975 6. Performing Organization Code 7. Author(s) 8. H. W.Steinhoff, Nel Caine (Eds.) Performing Organization Report No. 9. Performing Organization Name and Address 10. Work Unit No. Depa'rtment of Watershed Sciences Colorado State University 11. Contrac.t or Grant No. Fort Collins, Colorado 80521 14-06-0-7052 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Bureau of Reclamation Interim Progress Report Building 67, Denver Federal Center January 1973-June 1974 Denver, Colorado 80225 14. Sponsoring Agency Code 15. Supplementary Notes This document is a compendium of related physical and biological studies which are attempting to assess the ecological Impact of the Upper Colorado River Basin Pilot Froject. ,It represents a cooperative effort between Colorado State University, the University of Colorado and Fort Lewis College. 16. Abstract The results of the San Juan Ecology Project's third operational year are presented in this report. The project is administered as two major teams, the Forest and Alpine Tundra Ecosystems. Above timberline, it was found that an artificial increase in snowpack, produced by snow fences, does affect plant production, plant decomposition, seed germinabillty and early season phenological development; no effects on late season phenology were noted. Below timber !Jne, herbaceous plants at higher elevations and on ,north slopes mature and flower at a smaller size than those of the same species at lower elevations and on south slopes (i.e. areas of shorter~lying 'snow),. Several phenological parameters of spruce and aspen growth are apparently related to seasonal snow variation through changes in air and soil temperature. It has been shown that the early snowmelt period is definitely one of high moisture stress in trees; a model is being developed to relate this stress to environmental variables. Allometric equations have been developed _to relate tree biomass production to tree diameter and height, so that biomass may be related to snowpack variation. Forest phytosociological studies indicate that long term increases in moisture may gradually alter forest composition. e.g. from fir to spruce and from st~ble to successional aspen and fir. Above treeline, population characteristics of pocket gophers are being related to snow depths. Below treeline. evidence is accumulating that, within limits, population size Of some small ma'mmals under study is inversely relatea t6 snow depth. Elk appear to prefer oak communities on south aspects. where penetrable snowdepth is less than 35 cm. at time of maximum accumulation, but they will tolerate up to 70 em. depth if all available areas are under deep snow cover. Geomorphological studies indicate that summer erosion is the overriding factor in alpine soil movement, and that the San Juan area is not likely to be strongly influenced by the degree of climatic change which could be brought about by an increase in snowpack. An ecological overview is attempting to relate characteristics of alpine and forest study sites to the whole target area. No significant increases in silver concentration have been found on the target area after three winters of seeding, but definite increases have occurred in vegetation and litter at the-generator site understudy. No deleterious effects of silver iodide additions have been noted, either at the generator sites or in field application plots. The possibility of microbial conversion of insoluble to solubl,e silver forms has been observed. . . 17. Key Words 18. Distribution Statement alpine tundra, clouq seeding. Colorado, No Limitation ecology. ecosystems, forests, weather modification 19 Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified '. I:; ~ f , " , ~', ., " ~~ ~~ ~ _Y. " ( ;::- ff; }; :?: '. '.' ,,;.: " "::' f; 9.- ~." :0: -';.:, ( i-. l';' " '-o' ~, lie'",,"