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i-:CCU"'Grc.'\~ :':"fPACI_S OF .~~:.:?:-::I"\C!-.: AL:C-:;::~:-;-A7)O;, :r-: THE SA"X JlA... XOm;rAI!\S OF COLORl.DO --~!~ .....~...- CPAPTL~! I~7RODUCTI0N .1 I.:. 1\"€5, J..... S\';~t:nf:Y. H. ;.,'. Steinhoff. and W. \..'. Ho....ell ., This docuQent is the finnl rep0rt of the San Juan Ecology Project (SJEP) ~hich has been supported by the United States Bur~au of Reclamation under Ccntract No. 1~-D6-D-]052 irow. 1970 to 1975. An earlier study. that was prepared as a proh~em analysis, has been re- ported previously (SJEP. Phase 1 Final Report: Teller et al. 1970). ThE:: prescnt report (Phase II) does not include any of the early. preparatory mate~ial~ SUMMARY OF KEY CO~CLUSIONS This Summa . condenses the evaluation of ecologic imPacts due to varving snowpack in the San uan Moun-- tains. It is based on a study of the influence of a snovfall which is quite variable in both space and . time. Direct observation of the effetts of snovpack augmentation were not possible during the 5-year lite of the San Juan Ecology Project. but the relationships _ established D~tween ecosystem components and snow conditions allow the esti~tion of possible effects of long-tena successtul cloud seeding. The statements which follow treat the main ecosystem . components in order. The impact. of snowpac:k augmen-: tation on each ecosystem component is arranged accord- ing to tbe nature of the environmental change which produced the effect. . The basic environmental changes are the 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 tbe chain which have a significant impact On ecosystem components are: (1) lower soil temperature in the spring, (2) more moisture in the spring. (3) deeper sDowpack, and (4) more silver. This summary includes only statements verifiable from the data. with causal connections and conclus1ons that would be accepted bv scientific peers in environ- ,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 1n 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 througb the use of terms such as "may-be" or"probably". or which are label1'ed as . "broad significancell or "implications." Many other findings, which are not directly related to the effects of snowpack augmentation on 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. !!!E.!!. rOnly two envirO~lm~nral chan~e5 I.!hich &'light be induced by increased snowfall hn~c been found to relate signif- icantl. to lants in th(; San Ju.,n Mountains; lo....er soil. temperatures God m0rc sol rno~sture. _- Lower Soil Temperatures ~ :.. 10it18t10o of shoot elongation was delayed for plants. oth in the: tundra and forests ;]~ n ~cslllt '..If lOIo.er soil temperatures 3ssoclnte 10' t 1 a eeper snm..1lac', for the species studied. These includeci Englemann spruce (Picea en~elnann11). quaking nspen (Po~ulus trc&'Iuloides), Thurbcr feSCue (~~ thurberi). and numerous herbaceous species in both the tundra anri forest oea- dows. e delay was mo~t apparent in S?eCie5~ith ~rowth points in the ~e ate zone 0 o~er. temperatures at the ground level.. This includes pri- marily the herbaceous species. The growth regions of trees, in the cambium and terminal buds. ~ere affected more indirectly, possibly through'soil temperature effects on_root function. From this a less clear re- lationship bet~een gro~th inception and snovPack was anticipated although ~here 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 hiRh durtnR the period of sno~elt and decreased pramaticallv 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 s~owpack.. Resultant annual biomass Rrowth of spruce was remarkably constant from year to year. unrelated to snowfall. Aspen wag more variable 1n annual biomass production. Aspen growth inception was delayed by a later _snow clear d~te. but we did not determine whether or not this was directly ~. linked to variations in biomass production. . The delay in be~innid~ of ~rowth persisted throURh the other stages of the life cycle of most plantsJ but with less magnitude. There seemed universally a com ensation tactor which permitted every species to complete. its annual cyc e 0 eve opment cac summer. regar4!ess at snowpack deptb. t%cept tor spruce, there ~as no S1mliar compensatory mechani~ for biomass production. tn most herbaceous species of the tundra. biomass production vas inversely related to depth of snawpack. No effect was found on either initiation of development or biomass production of oak (Quercus ~ambellii). 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 io 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)J and finally to Engle~nn 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 mo~e mesic or even hydric communities. This could be expected to result in an increase in frequency of the rarer species. A dendrochronologic survey of ponderosa 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 shov an increase in gro~th if ,cloud seeding were to add to mid-~inter snowfall. No such relationship was found for Engelmann spruce. the only other species on which dendrochronologic work has been conducted 1n this study. . Animals ..:. Only the lOYer soil temperature and' greater snov depth. which eight be expected to follov an increase in snow- fall. have been found influential on ani~~l activity.