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. . LG,~'~i_~..-,- ~}'AC.l.~l !-~:~:,;?~CK A:':G:~,F..:,TA}'10l~ :S 7P.E SA.'; JlA.~ HOm;TAI~;S OF COLOkADQ CP.APTER I INTRDDVCTIuN h'€s, J. ~. S\.:~(:nE:Y. H. ....'. Steinhoff, and \"'. W. Ravell This r.ocUl:Jcnt is the fin;;.l repC'rt of tb~ San Juan Ecology Project (SJEP) ~h~ch ~as Deen supported by the United States Bure~u of F.~21a~ation unGer Ccntract No. 14-06-D-7052 fr')tr, 1970 to 1975. An earlier study. that ~as prepared as a prohle~ analysis, has been re- ported previously (S~EP. Phase I Final Report: Teller et a1. 1970). Th~ pn-sl2nt report (Phase II) does not include any of :he cdrly, preparatory material. SUW.ARY Of fT:{ CO~~CLL'SID!iS this Summar- condenses the evaluation of ecologic impacts due to varvin~ sncvpack in t e San ueo Moun-- tains. It is based on a study of the influence of a snowfall ~hich is quite variable in both space and time. Direct observation of the effects of sno~ack au entation were not possibl~ during the 5-year lite of the San Juan Ecology Project. but the relat ons ps ~stablished between ecosystem components and snow conditions allow the estiL~tion of possible effects of" long-term successful 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 th~ effect. The basic environmental changes are the ~ddition 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 cbain which have a significant impact on ecosystem components are: (1) lo~er soil temperature in the spring. (2) more moisture in the spring. (3) deeper snoYp3ck. and (4) more silver. This summary includes only statements verifiable from the data. with causal connections and conclus~ons that would be accepted by scientific peers 1n environ- , mental disciplines. SpeculatIon about causal links in the chain, or e~tension of implications beyond effects ~hich were studied in the chain, and where the extension involves application of general ecologic understanding, are avoided in this summary. Such appropriate 6cIen- tific conjecture can be tound in Chap~ers 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 Io.'hich are labelled as "broad significance" or "implications." Many other findings, ~hich are not directly related to the effects of sno~~ack augmentation on the indicated ecosystem components are a natural part of such studies. For a surr~ary of these findings reference is made to the abstracts of individual reports or to the details of the individual reports themselves in Chapter IV. Plants ..Only t...'o env~rG;)mt2r,l:..1 cnallj.;es l-..hich rdght be induced by increased ~no~"fDl1 h,,\'e b(,'en found tc relate Signif- icantly t.o p],l.!;tl; in the Sa71 JU:lll Nountains; ]o\.;er soil te.mperatures bnd I.K're soil rnolsture. - Lo~~r Soj] Temperatures ..3:niti03t:!on of shoot elongation .....as delayed fer pl.1nts both 1n 'the tlmdrn ~nd forests [,5 a :-(;~aJl [ '_'f 10~'cr soil tern eratllTeS a!;sorj.,;tE::d ....itl1 a deeper sno~'p;;cF for .the species studied. Th~se jncJudea Eng e~ann spruce (Pice.. enge-!'p~;. quaking <.lsp€-n (Po;->~ ~~), Thurber f~$cu€ (I.:.Htu_~ _~rbf':..~j), nnd numerOllS herbaceous species in both the tundra and forest t~a- do~s. e delay was most apparent in s?eci€::s~ith ~~o~th points in the 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 and terminal buds. ~ere affected more indirectly, possibly through soil temperature effects on root function. From this a less clear re- lationship between growth inception and snowpack vas anticipated although there ~as a general correlation of bud burst dates for both spruce and aspen vith the SQOV clear dates. Moisture stress 1n spruce vas un- usually hi~h durin~ the period 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 erowth of spruce was remarkably constant from year to year, unrelated to snowfall. Aspen was more variable in annual biomass production. Aspen growth inception was delayed by a later snow clear d~te. but we did not determine whether or Dot this was directly linked to variations 1n biomass production. .The eela, in be~inn~~ of ~rovth persisted throu~h 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 co~plete its. annual cycle of development each summer, regardless ot snowpack depth. t%cept tor spruce. tnere was no s1mliar compensatory mechanism for biomass production. In most herbaceous species of the tundra. biomass production was inversely related to depth of snowpack. No effect was found on either initiation of development or biomass production of oak (Quercus Kambellii). pre- sumably because even in a deep snow year the snow had always disappeared from oak plots before the earliest date of growth 1nitiation. - Non Moisture Phytosociological studies in both forests and tundra showed that plant communities were arranged along snow clear date gradients. In the forests oak gives ~ay to aspen. then to subalpine fir (Abies lasiocarpa), 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 more mesic or even hydric co~unities. This could be expected to result in an increase in frequency of the rarer species. A dendrochronologic survey of ponderosa pine (~ 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 ~ould presumably sho~ an ir.crease in gro~th if cloud seeding \Jere to add to mid-winter sno~.fall. !:o 'such relationship .....as found for Engelmann spruce, the only other species on which dendrochronologic ~~rk has been conducted in this study. AniI:la]s Only the 10~r soil temperature and greater sn0~ deyth. ~hich mi~ht be expected to follo~ an 1ncrease in snow- fall, have been found influential on anirr~l activity. ! i