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<br />OOllE? <br /> <br />creation of openings in forest stands due to natural <br />causes, forest harvest operations, grazing by wildlife and <br />domestic stock, and any other change to the climatic and <br />cover conditions existing at any point in time and space." <br />[19, pp. 1-31 to 1-34) <br /> <br />The Sierra Cooperative Pilot Project Environmental Assessment discusses <br />the effects of precipitation increases on herbaceous plants and grasses <br />and states: <br /> <br />"With regard to precipitation, it is generally believed <br />that the average annual rainfall is the basis for the <br />species composition of an area; and that it is the end of <br />the curve (the drought or below-average situation) that <br />determines whether a given species will continue in an <br />area. Shifts in moisture through the middle range of <br />moisture availability will affect growth and biomass, but <br />do not have a controlling impact on composition of the <br />plant community. <br /> <br />"It would require a significant increase in moisture supply <br />over a middle to long-term periOd in order that competing <br />plants would invade an area and push existing species <br />out. <br /> <br />"Small shifts in species may occur due to late-lying <br />snowbanks at small localized sites if the wind and other <br />snow-depositing controls extend the same snowbank each <br />season during an extended research period. Plants at the <br />edge and downslope of an extended snowbank will increase <br />growth somewhat due to the increase in moisture from the <br />melt. However, this effect could be offset to a degree, or <br />entirely, by decreases in soil temperature. During years <br />within the average spectrum, no noticeable effects will <br />occur. In other than average periods, some increase or <br />decrease in plant growth may detectable, but no change in <br />composition would be expected." [12, pp. 85, 86 et seq.) <br /> <br />The Skywater Programmatic FinaL Environmental Statement reached the <br />following conclusions with regard to the impacts of winter precipita- <br />tion variations on herbaceous vegetation: <br /> <br />"The study situations encompassed seasons of naturally <br />heavy and naturally light snowfall, and of naturally early <br />and naturally late snow cover. In addition, artificial <br />snow accumulations were deposited on portions of some study <br />areas in both forest-meadow and alpine-meadow locations. <br />Preliminary results indicate that heavy or late-lying snow <br />tends to shift the growing season to a later date, but not <br />to affect its length. In delayed seasons, species were <br />observed to complete their growth cycles and set seed. <br /> <br />20 <br />