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~ ,1 '. .~ I , ,I ~\ ,1 i \ I 1 ! .\ ;i I .~: . ,~ " ~ 1 \ t j , I I , , i f ! I . , "i i " , ,'''' , CHAPTER II A DISCUSSION AND SYNTHESIS II Nel Coint ?I C P. Patrick Reid, P. J. Webber, and Donald A. Klein vat!on. With the exception of Wolf Creek Pass, no all-weatber roads cross the mountain area and much of it lies within the Weminuche Wilderness. INTRODUCTION This chapter is intended to dr<l'l.' tor,ether the main conclusions of ChanteT IV of this report ~ith regard to the influence of cloud seedin~ on the terrestrial ecosystems of the San Juan Mountains. :Pollowing a brief description of the field area, the ecosystem components are considered separately and then the p06sibility of linked interactions among them. which may lead to either damped or amplified reeponses to snowpack augmentation, is discussed. This treatment requires some speculation about poten- tial ~pacts, especially long te~ ones, since not all of tbe predictions made here are based upon statis- tically proven relationships. The speculation is, however, that of scientists who have worked in. the tSan Juan Mountains for S years and so is usefuily included in a general discussion of ecological effects, bearing in mind the increased risk of error which such speculation entaUs. During the 5 year life of the research reported here (1970-1975), the San Juan Mountains have' been the site of '8 pilot project designed to teat the operational effectiveness of snowp8ck aUgra~ta~' tioa through a randomized seeding exper~ent. Or1J;inally. it was anticipated that the project .,. would Rive a 15 ~ercent increase in winter snowpacksi that is ahout one half of the expected full poten- tial of vinter cloud seeding in the area. ~ubsequent . evaluation of the cloud ~eeding experiment has led to the conclusion that actual snowpack augmentation was below the anticipated 15 percent level (Howell, this vol~ p. 5). Any artificially caused increase in the snowpacK of the San Juan Mountains has been imposed on a region in which precipitation and snow acc~at~on is naturally ~ig~ly var1able: annual snowfall there ranges between 35 percent less and UU percent greater than the annual mean ot 4U cm water equivalent (w.e.) measured over a 25 year period. ~ny of the estimates of ecologic impact made in this study are based on the potential 30 per- cent increase in mean snowpack accumulation that was originally assumed to be poss~ble in an operational phase ~f winter cloud seeding. TIlE FlEW AREA In southyestern Colorado, the Continental Divide makes a wide bend to the vest around the headw8tu8 of the Rio Grande and through the San Juan Mountains. The target area for cloud seeding has been a 3400 km2 area in the southern and eastern part of the range, extending from the. Colorado-New Mexico stat.e line to the Needle Mountains. Most of the field 'investiga.. tions of the San Juan Ecology Project have been conducted in this target area (Figure I, Chapter I). In the target area, the Continental Divide runs almost east-west and subsidiary ridges extend from it to the south or southwest betweeo tributaries of the Sao Juan River. The topography of the area is generally rugged with some of the peaks ~xceeding 4250 m ele- 1/ In Steinhoff, Harold W. and Jack D. lves (Eds.) 1976. - San Juan Mountains, Colorado. Final Report, San Juan Fort Collins. ~I Present Address: Geologically, this is a young part of the 50uthern Rockies and is composed largely of Tertiary volcanic tuffs and lavas, although metamorphic materials of Precambrian age are exposed extensively in the Needle Mountains and Grenadier Range at the western end of the target area. Mesozoic sedimentary materials are found only at lower elevations: This diversity of parent materials, combined with the changes of climate and vegetation due to elevation and a his- tory of multiple late-cenozoic glaciations, has ; produced a complex pattern of 80i1s and surficial depositsi however, this complexity is typical of the southern Bocky Ifoun~ains. . tf I . - .s,e.c.:TU>l'~.-O."'" e"'- CONCLUSiONS I I,' >l"{, ,The-~esult8 of" the San Juan Ecol02v Proiect SU~Rest that,~here should be no immediate& larKe-scale aces on the terrestrial ecos stems of these" mountains followinR an addition of up to percent of the,normal snowpack, but with no addition to ~ raxitDUflt. snowpaclts. Further. much of the work re- ~p'orted b~re.su22est8 that compensating mechanisas within the studied ecosystems are such that any impacts would be buffered, at least for! short periods of time and of lesser ma itude thaD the chao ea in snow conditions, required to pr uce them. POwever, .some 'parts.of the ~u~tain ecosystem are much more susce~tible to chanRe9 in snow conditions 'yhan others. so important local effects are oossible. in general, these susceotible components are very small harts of the entire system but their economic O~ est etic value may be much g~eater than ~belr mass or area SUR~est. Remedial action is possible in most of these cases but has not been studied in this project. Our work has shown three ecosystem com nents to be most 8usce tible to increased snow all: snowbank situations at e evations above treeline; (21 elk herds (in other counta1n ranges other big game speCies may be similarly affected)i and 3) so~ small mammal 0 ulations, es ec1all the deer mouse. Not al1'0 these impacts are necessaril deleterious; an increase in the area of snowbank edge habitats in a pine area may, or examp e. increase the niches available for rare plant species. inall even in the small areas where we predict rea test impacts from increased snow a ,t e c ange6 nvolved are un e y to approac t e magn u e 0 at er man-ma e mpacts on mounta n ecosystems. ow- ever, it shOuld be rememnerea tnat tney may act in phase with other man-made impacts and with natural climatic changes, in which case the total effect could be much greater than our studies suggest. ~, Ecological impacts of snowpack Ecology Project, Colorado State augr.lentati(1n "in t'llfc University rtl~l.. INSTAAR, University of Colorado, Boulder. Colorado 80309. -29- A-13-S