WMOD00246 - Laserfiche WebLink

Home Browse Search

..._w_. .~ -, ,""'" -~ . " , L-.Gt;I.~I~[~o. l-~~C].~_Q..t. .PF~oir~ft. AL1GXENTJf!lON IN TilE e..AN JuAN MOUNTAINS OF COLORADO CHAPTER 1 INTRODUCTION .1. r. I\'es. J. M. S~ceney. H. ~o Steinhoff. and W. W. Howell This document 1s the fi.nal report of the San Juan Ecolog}' Project (SJEP) \.tole" has been supported by the United States Bureau of Reclamation under Contract No. 1~-06-o-7052 from 1970 to 1975. An earlier study, that was prepared as a prohlem analysis, has been re- 'ported previously (SJEP, Phase I Final Report: Teller et al. 1970).' Th~ present report (Phase 11) does not include any of th~ early, preparatory material. SUMMARY OF KEY CONCLUSIONS This Summary condenses the evaluation of ecologic 1~acts due-to varv1n~ snowpaCK in the San Juan Moun-- tains.' It,is based 'bn a study of ,the influence of a snowfall-'which. is 'quite variable -1.n- 'both space and' . t1me~. O!rect'observation of the effects of snovpack . .~".ugmentation were not possible during the 5-year lUe of the'S4n'Juan ~eolo Pro ect, but the relationships eeta _he etWeen ecos stem co onent. an snow oond!tion.,~llov the e.t~~tion 0 poa. e e Bets of, long-te~ successful cloud seeding. ';"." ,. The Btacements whieh follow'treat the main. ecosystem ,components in ~rder. The impact '-of snovpaclr. 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 the ~ddition of more snow and more 8ilver~ Such changes could initiate a chain- of effects that would radiate throughout the ecosystem. The first links in the ch41n.,~1ch'have a significant impact on eCOBY8t~ components :are:' (1) lower 80i1 temperature 1n the spring, (2)" more moisture in the spring, (3) deeper snowpack. ando'(4) more silver. This summary includes only statements verifiable from the data. with causal connections and cancIuGtons that would be accepted by scientific peers 1n environ- ',mental disciplines. Speculation about causal links 1n the chain, or extension of implications beyond effects . which were' studied 1n the chain. and where the extension involves application of general ecologic understanding, ~re 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 apec- 'ulative by implication through the use of terms such 86 Ilmay be" or"probably", or which are labelled 88 "broad' significance" or "implications." Many other findings, vh1ch are not directly related to the effects of snowpack augmentation on the indicated ecosyste~ components are a natural part of such studies. For a s~ry of these findings reference is made to the abstracts ~f individual reports or to the detail~ of the individual reports themselves 1n Chapter IV. Plants "Only twO enviro;lJn~nt"aJ changes \!hich might be induced by increased Rnot.Jfall hll\'c been found to relate signif- icantly to plal1tl> in the San Junn Mountains; lo....:er soil temperatures and rn0re soil moisture. _ Lower Soil Temperatures .inittatil'ln of shoot elollj.tAtion \o:as delay~d for pla-nts orh 1n the tundra and f()rest~ ns 11 result 01 lo....:(!r Boil temperatures assoC'j.ate:d .... t 1 a eeper sno......pac 0 for . the species studied. These includeo Englemann spruce l (f1fE engeLT:!!..t!.1l.;..:). quaking ilSpE:'l1 (POjl~~ t.rcmuloidcs), Thurber f~sc:u~ (X~~~ _t hU'rbp;,..\.~i), :lnd nlil:ld"OllS herbaceous species in both the tundra and forest roea- do'-'s. e dele \laB most apparent in species with ~rowth points in t e ~e ate zone 0 oW~r temperaturu 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 te~perature effects on root function. 7rom this a less clear re- lationship between growth incept10n and snowpack was anticipated although there \las a general correlation of bud burst dstes for both spruce, and aspen with the snow clear dates. Moisture stress in spruce was un- usually hiRh durin2 the period of snowmelt and decrea8e~ pramaticallv at about the. snow clear date~ This did not affect the annual tot.l rad~l srowth of spruce. vhlch initiated 2 to 4 weeks earlier than bud burst, apparently independent of 8nowp.ek~j:Resultant annual biomass Rrovth of spruce ~.. rem4rkably constant from ear to year, unrelated to anovfall. Aspen was more var a e n annua omasa pro uct on. Aspen growth inception ~as delayed by . later snow clear d~te. but we did not determine whether o~-not this vas directly linked to variatione ,in b1~~~~.product10n., The dela, in beRinnldk of Rrowth persisted throuRh the other stages of the life cycle of most plants, but with less magnitude. There seemed universally 8 compensatlon ractor wh1cb permltted every species to complete its, annual cycle of develo~ent each .summer, regardless ot snowpack depth. ~cept tor spruce, tfiere was no 81ml~ar c~pen5acory mechanism for bioma8s production.',. In most herbaceous species of the tundra, biomass production was inversely related to depth of snowpack. No effect vaa found on either in1tiation of development or biomass production of oak (Quercus ~ambellii). pre- sumably because even in a deep snow year the snow had alvays disappeared from oak plots before the earliest date of growth initiation. - liore Moisture Phytosociological 8tudies in botb 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 (~lasiocarpa), and finally to Englemann spruce as the snow clear date extends later into the year. The change was less obvious in the dr1er communities, i.e. 1n oak. The tundra changed from xeric (drier) to more mesic or even hydric comm9niries. This~could be expected to result in an increase in frequency of the rarer species. A dendrochronologlc 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 yould presumably shov an increase in gro~th if floud seeding were to add to mJd-winter snowfa)l. No 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.... depth, which mi~ht be expected to follow an increase in snow- fall. have been found influential on animal activity.