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<br />CHAPTER 1 I
<br />A DISCDSSION .~~D S~THESIS II
<br />
<br />INTRODUCTION
<br />
<br />:\eJ C;~il;!. =- . C. P. P.>trick Reid. P. J. \.'ebber, and Donald A. Klein
<br />
<br />vatian. \.'ith the exception of ~olf Creek Pass, no
<br />all-~eather roads cross the mountain area and much
<br />of it lies within the Weminuche ~ilderne~s.
<br />
<br />This chapter 1s intended to dr~~ to~ether the main
<br />conclusions of Chdvt~r lV of this report ~ith
<br />regard to the influence of cloud seeding on the
<br />terrestrial ecosystems of the San Juan Mountains.
<br />Following a brief description of the field area, the
<br />ecosystem components are considered separately and
<br />then the possibility of linked interactions among
<br />them, which may lead to either damped or amplified
<br />responses to snowpack augmentation, is discussed.
<br />This treatment requires some speculation about poten-
<br />tial impacts, especially long term ones. since not all
<br />of the predictions made here are based upon statis-
<br />tically proven relationships. The speculation is.
<br />however, that"of scientists who have vorked,in the
<br />San Juan MOuntains for 5 years and so is usefully
<br />included in a general discussion of ecological
<br />effects, bearing in mind the increased risk of error
<br />which such speculation entails.
<br />
<br />During the 5 year-life of the research reported
<br />here (1970-1975)~ the San Juan MOun~a1ns have'
<br />beeD the site of a pilot project designed to" test
<br />the operational" effectiveness of snowpack augmenta-
<br />tion through a randomized seeding experiment.
<br />Ori~iDally. it vas anticipated that the project
<br />would Rive a 15 percent increase in winter snowpacks;
<br />that is about one half of the expected full poten-
<br />:t18l of winter cloud seeding in the area. Subsequent
<br />evaluation of the cloud ~eed1ng experiment has led to
<br />the conclusion that actual snowpack augmentation was
<br />below the anticipated 15 percent le~el (Howell, this
<br />vol. p. 5). Any artificially caused increase in the
<br />snowpack of the San Juan Mountains has been imposed
<br />on a region in which precipitation and snov
<br />accumulation is naturally highly variable: annual
<br />snowfall there ranges between 35 percent less and
<br />HO percent greater than the annual mean at 4U cm
<br />water equivalent (v. e.) measured over a 2S year
<br />period. ~ny of the estimates of ecologic impact
<br />made in this study are based on the potential 30 per-
<br />cent increase in mean snowpack accumulation that was
<br />originally assumed to be possible in an operational
<br />phase .of "triter cloud seeding.
<br />
<br />TIlE FIELD AREA
<br />
<br />In southwestern Colorado, the Continental Divide
<br />makes a vide bend to the west around the headwaters
<br />of the Rio Grande and through the San Juan Mountains.
<br />The target area for cloud seeding has been a 3400 km2
<br />area in the southern and eastern part of the range,
<br />extending from the Colorado-New Mexico state line to
<br />the Needle Mountains. Most of the field --investiga-
<br />tions of the San Juan Ecology Project have been
<br />conducted in this target area (Figure I, Chapter I).
<br />
<br />In the target area, the Continental Divide runs almost
<br />east-west and subsidiary ridges extend from it to the
<br />south or southwest between tributaries of the San
<br />Juan River. The topography of the area is generally
<br />rugged with some of the peaks ~xceeding 4250 m ele-
<br />
<br />11 In Steinhoff, Harold W. and J~ck D. Ivcs (Eds.) 1976.
<br />- San Juan Mountains, Colorado. Final Report, San Juan
<br />Fort Collins.
<br />~I Present Address:
<br />
<br />Geologically. this is a young part of the southern
<br />Rockies and is composed largely of Tertiary volcanic
<br />tuffs and lavas. although metamorphic materials of
<br />Precambrian age are exposed extensively in the ~cedle
<br />Mountains and Grenadier Range at the ~estern end of
<br />the target srea. Mesozoic sedimentary materials are
<br />found only at lower elevations; This diversity of
<br />parent materials, combined with the changes of
<br />climate and vegetation due to elevation and a his-
<br />tory of multiple late-cenozoic glaciations, hqs
<br />produced a complex pattern of soils and surficial
<br />deposits; however. tMs complexity is typical of
<br />the southern Rocky Kountains. tf J
<br />. ' -',SecTi.""s-Q,...,; '" -
<br />colicLiJsioNS, ~', "". c ",'
<br />
<br />;":"f<:;:":""\;' ,1-->11.':-'
<br />
<br />".~"' "" -0;","
<br />
<br />The results of the San Juan &colo~ Pr01ect ~Rest
<br />that there should be no immediate. larRe-scale " ~
<br />_iCDacts on the terrestrial ecosystems of these.
<br />mountains followinR an addition of up to JO percent
<br />, of the. normal snowpack, but yith DO addition to
<br />;.. r8xiunuo" snowpacks.". Further. much of the work re-
<br />ported ,~ere sunests that compensating mec.'lanisms
<br />within the studied eCOsTstems ~re such that any
<br />ftlpacts would be buffer!';". at least lfar short periods
<br />00:;"" of time. and of lesser lllsKtlltude than the changes
<br />in snow conditions required co produce the=.
<br />
<br />Howe~er~ s~m~ "'~art~' ~f\h~-.~~~~tai~ eco"~"~~t~ are
<br />
<br />much more suscePtible to chan~es in snow conditions
<br />than others, so important local effects are possible.
<br />n general, these susceptible components are very
<br />small parts of the entire system but their economic
<br />or esthetic value may be much greater than their
<br />mass or area SUR~est. Remedial action 1s possible
<br />in most of these,cases but has not been studied in
<br />this project. Our work has shown three ecosystem
<br />components to be most susceptible to increased"
<br />snowfall: 1) snowbank situations at elevations above
<br />treeline; (2J elk herds (to other mountain ranges
<br />other big game species may be similarly affected);
<br />and 3) some small mammal populations, especially
<br />the deer mouse. Not all of these impacts are
<br />necessaril deleterious; an increase in the area of
<br />snowbank edge habitats in alpine area may. or examp e,
<br />increase the niches available for rare plant species.
<br />
<br />Inall even in the small "areas where we predi€t
<br />rea test impacts from increased snow a . t e c anges
<br />nvolved are un i e y to approac t e magn u e 0
<br />ot er man-ma e mpacts on mounta n ecosystems. ow-
<br />ever, it should be remembered tnat ~ney may act in
<br />phase with other man-made impacts and vith natural
<br />climatic changes, in which case the total effect
<br />could be much greater than our studies suggest.
<br />
<br />___ _________J
<br />
<br />Ecological impacts of snowpack
<br />Ecology Project. Colorado State
<br />
<br />augQentation in t!l~
<br />University l'\.t-l..
<br />
<br />INSTAAR, University of Colorado, Boulder. Colorado
<br />
<br />80309.
<br />
<br />A-13-5
<br />
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