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<br />"Bo lewood product ion of spruce-fir stands was found to <br />remain constant over a 20-year study period, and it was <br />thought that productivity is mainly under genetic control. <br />Tree biomass was shown to undergo severe perturbat ions <br />attributable to catastrophic events such as windthrow, <br />insect outbreak, or fire. It was considered debatable <br />whether changes in snowpack could positively or negatively <br />influence these disturbance events. <br /> <br />IIMeasurement s of water stress in forest vegetat ion resulted <br />in the identification of two periods of elevated stress, <br />one immediately preceding snowmelt, the other later in the <br />season, after the exhaustion of soil moisture held over from <br />winter. If precipitation management were to extend the date <br />of moisture release from snow cover, this might extend the <br />duration of the spring period of moisture stress. The <br />opinion was also expressed in the findings that the major <br />effect of this high-stress period would be to reduce photo- <br />synthesis rather than cell division, since the trees were <br />found able to rehydrate at night. As long as the stress <br />period occurs before the beginning of phenological activity, <br />little change in growth would be expected. Significant <br />alteration in growth would result only if precipitation <br />management were to delay snowmelt into the period of active <br />growth.1I [2, p. 3-111J <br /> <br />Two Sierra Ecology Project Workshops examined the effects of precipita- <br />tion increases on vegetation. Workshop I, IIAn Evaluation of Possible <br /> <br />25 <br />