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,I [COLOefCAl r~AGT1> OJ_ ~~._'::';~T!~c~: AUG}'(E,\"TATIQr{ IN THE SA.~ Jt;AN MOrn;TAINS OF COWkADQ CHAPTER I I~rrRoDucrION 1.:' IVes. J. "" S".eeney. H.~. Steinhoff, and W. Y. Hovel1 This document 1s the final report of the San Juan Ecology Project (SJEP) ....hich hils been supported by the United States Bureau of Reclamation under Contract No. 14-06-0-7052 from 1970 to 1975. An earlier study. that ~as prepared as a problem analysis, has been re- ported previously (SJEP, Phase I Final Report: Teller et al. 1970). Th~ present report (Phase II) does not include any of the early, preparatory material. SUMMARY OF KEY CONCLUSIONS This Summar condenses the evaluation of ecologic impacts due to varying snowpac in the San uan oun-- tains. It is basea on a study of the influence of a snowfall which is quite variable in both space and time. reet observation of the effects of snowpack au~ntation were not possible during t e -year e of the San Juan Ecology Project. but the relationships established between ecosystem components and snow conditions allow the estimation of possible effects of long-term successtul cloud seeding. The statements which follow treat the main ecosyStem components in order. The impact of snowpack augmen- tation on each ecosystem compOnent is arranged accord- ing to the nature of the environmental change which produced the effect. The basic environmental changes are th~ addition of more snow and more silver. Such changes could initiate a chain" of effects that would radiate throughout the ecosystem. The first links in the chain which have a significant impact on ecosystem components are: (1) lower soil temperature in the spring. (2) more moisture in the spring, (3) de~per snowpack, and (4) more silver. This summary includes only statements verifiable from the data. with causal connections and conclusions that would be accepted by scientific peers in environ- f mental disciplines. Speculation about causal links in the chain, or extension of implications beyond effects which were studied in the chain, and where the extension involves application of general ecologic understanding, are avoided in this summary. Such appropriate scien- tific conjecture can be tound in Chapters II and III and in segments of individual reports that are spec- ulative by implication through the use of terms such as "may be" or"probably". or which are labelled as "broad significance" or "implications." Many other findings, which ar~ not directly related to the effects of soawpack augmentation 00 the indicated ecosystem components are a natural part of such studies. For a summary of these findings reference is made to the abstracts of individual reports or to the details of the individual reports themselves in Chapter IV. ~ ,.Only two envirOillllentaJ change:; ".,'hich might be induced by increased sno~fall hnve been found to relate signif- icantly to plants in tht:: San JU:ln MOuntains; lower soil temperatures and m(lre soil moisture. - Lower Soil Temperatures initiation of shoot e]on!-!lltion ....as delayed for plants otn in tn(! tundra and forests 8S a :-esult ot lo","Cr . soil temperatures asso<'iCitEd ..dt 1 a eeper sn01.'Pac' for the species studied. These includeQ Englemann spruce 1 ~ engelrnannJ.J.j, qu.':Iki.ng aspen (Po~ulus trem~loides), Thurber fescue (T:::.estU(;3 thurhf':.!}), and numerous herbaceous species in both the tundra and forest cea- do1.7s. e delay was most apparent in species 1.7i th ~rowth points In t e mme ate zone 0 ower temperatures at the ground level. This includes pri- marily the herbaceous species. The gro~th regions of trees, in the cambium snd terminal buds, were affected more indirectly, possibly through soil temperature effects on root function. From this a less clear re- lationship between growth inception and sno~ack vas anticipated although there was a general correlation of bud burst dates for both spruce and aspen with the snow clear dates. Moisture stress in spruce was un- usually hi~h durin~ the neried of snowmelt and decreased dramatically at about the snow clear date. This did not affect the annual total radial growth of spruce. which initiated 2 to 4 weeks earlier than bud burst. apparently independent of snowpack. Resultant annual biomass ~rowth of spruce was remarkably constant from year to year, unrelated to snowfall. Aspen was more variable in annual bioll3ass production. Aspen growth inception was delayed by 8 later snow clear d~te, bu~ we did not determine whether or not this was directly linked to variations in biomass production. The delay in beainnidg of growth persisted throURh the other stages of the life cycle of most plants, but with less magnitude. There seemed universally a compensation tactor which permitted every species to complete l~s annual cycle of development each summer. regardless ot snowpack depth. LXcept tor spruce, there was no S1mi~ar compensatory mechanism for biomass production. In most herbaceous species of the tundra, biomass production vas inversely related to depth of snowpack. No ~ffect was found on either 1nitiation of development or biomass production of oak (Quercus ~ambel111). pre- sumably because even in a deep snow year the snow had always disappeared from oak plots before the earliest date of growth initiation. - More Moisture Phytosociological studies.in both forests and tundra showed that plant communities were arranged along snow clear date gradients. In the forests oak gives way to aspen. then to subalpine fir (Abies lasiocarpa), and finally to Englemsnn spruce as the snow clear date extends later into the year. The change was less obvious in the drier communities, i.e. in oak. The tundra changed from xeric (drier) to more mesic or even hydric communities. This could be expected to result in an increase in frequency of the rarer species. A dendrochronologic survey of ponderos8 pine {Pinus ponderosa) immediately outside the target area showed its growth on dry sites to be associated with December precipitation. The relationship is a direct one and pine would presumably show an increase in gro~th if cloud seeding were to add to mid-winter snowfall. ~o such relationship was found for Engelmann spruce, the only other species on which dendrochronologic ~ork has been conducted in this study. Animals Only the lower soil temperature and greater sno\ol depth, which mi~ht be expected to follow an ~ncrease 1n sno~- fall. have been found influential on animal activity.