WMOD00422

• Project Name: Colorado River Enhanced Snowpack Test
• Title: CREST - Environmental Assessment and Design Phase - Finding of No Significant Impact
• Date: 4/1/1981
• Weather Modification - Doc Type: Report

"Few circumstances were found where snow accumul ation appeared
to be a limiting factor in forest ecology. One of these, it was
suggested, was at some locations near tree line where ribbons
of forest alternate with glades in which snow accumulates. The
depth of snow, and the adverse effect of snow molds on survival
of young trees, apparently serve to stabilize the boundaries
of the glades. An increase in average wintertime precipitation
might lead to an extension of the area where the glade-and-
ribbon pattern prevails. On the other hand, in a New Mexico
sett i ng, the growth of spruce was found to be un i form in adj a-
cent areas even though the average snowpack differed by a factor
of more than eight.

"The conclusion was reached that a higher mean snow accumulation
probably would not affect primary productivity unless the
growing season was shortened." [2, pp. 3-111J

San Juan Ecology Study results agree with the Medicine Bow findings
and state:

"Bolewood production of spruce-fir stands was found to remain
constant over a 20-year study period, and it was thought that
productivity is mainly under genetic control. Tree biomass
was shown to undergo severe perturbations attributable to
catastrophic events such as windthrow, insect outbreak, or fire.
It was considered debatable whether changes in snowpack could
positively or negatively influence these disturbance events.

"Measurements of water stress in forest vegetation resulted in
the identification of two periods of elevated stress, one
immediately preceding snowmelt, the other later in the season,
after the exhaustion of soil moisture held over from winter. If
precipitation management were to extend the date of moisture
release from snow cover, this might extend the duration of
the spri ng peri od of moi sture stress. The opi ni on was al so
expressed in the fi nd i ngs that the maj or effect of thi s hi gh-
stress period would be to reduce photosynthesis rather than
cell division, since the trees were found able to rehydrate at
night. As long as the stress period occurs before the beginning
of phenological activity, little change in growth would be
expected. Significant alteration in growth would result only if
precipitation management were to delay snowmelt into the period
of active growth." [2, pp. 3-111J

Two Sierra Ecology Project Workshops examined the effects of precipi-
tation increases on vegetation. Workshop I, "An Evaluation of
Possible Effects of Weather Modification Upon Forest Insect and
Diseases in the American River Basin, California," noted the impacts
of a spectrum of events or activities upon the forest. These were
similar to those considered in the Medicine Bow and San Juan studies,
and included fire, grazing, logging, mining, recreation, and other
water management activities. Assuming that cloud seeding would occur
during years of below- and near-normal snowfall and produce a 10 to

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