ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

By changing wind patterns, clearcutting and partial cutting increase the suscep-
ti bil i t y of a stand to blowdown. Considerable windthrow occurred around the clearcuts
and within the partial cuts at Coram. Partially-cut sites on the Flathead National
Forest, at least in the vicinity of Hungry Horse Reservoir, frequently experience
bl owdown,
Residues left on the site slow air movement near the ground. The amount,
character, and placement of residues alter the wind speed with height. As a result,
evaporation and convective energy exchanges are a1 tered. Decreasing wind movement
decreases minimum and increases maximum temperatures.
POTENTIAL BIOLOGICAL CONSEQUENCES
Light
The amount, qua1 ity, and duration of 1 ight are significant to biological pro-
cesses, Light affects plant growth through both photosynthesis and the thermal
balance that controls transpiration and other internal physiological processes.
Light levels also affect the distribution and survival of other organisms,
Photosynthesis depends on a photochemical reaction that requires 7 ight energy to
split water molecules. If other factors of heat and COz are not 1 imiting, photosyn-
thesis increases in proportion to 1 ight intensity. Species have different intensity
requirements at which maximum photosynthesis will occur. Foresters have labeled
plants tolerant or intolerant. Certain of the chemical processes in photosynthesis
are temperature sensitive or COz sensitive. If either of these factors becomes
critical under adequate 1 ight, photosynthesis will decrease. Any one of these three
factors may become limiting in nature. Water is also critical to the photosynthetic
rate which can be limited by dry or cold soils. The viscosity of water is increased
in cold soils; this increases the resistance to movement and decreases the rates of
chemical reactions. High 1 ight intensities and high temperatures indirectly 1 i mi t
photosynthesis by causing damage to tissues. Excessive supplies of COP cause injury
a1 so.
Photosynthesis and respiration determine growth rate and production of biomass.
Respiration rates or oxidation of the carbohydrates produced in photosynthesis are
controlled by temperature asd oqgen levels. Plants with photorespiration exhibit
optimum respiration fro! 10 C-25 C. Plants without photorespiration exhibit optimum
respiration at about 35 C. Increases in temperature at certain levels increase
respiration and decrease net photosynthesis. Lee and Sypol t (1974) found that basal
area growth of a forest in West Virginia was reduced because high canopy temperatures
reduced dry matter production. These high canopy temperatures resulted from high net
radiation loads and cooler soi 1 temperatures, The cooler soil temperatures decreased
water absorption to the point where canopy transpiration exceeded the rate of water
absorption. Lee and Sypolt (1974) suggested that high net radiation levels (greater
than 0.7 cal/cm2/min) may directly reduce net assimilation.
Light, as indicated in the above discussion, can increase the temperature of a
plant leaf. This increase in temperature increases the difference between the vapor
pressures of air and of the internal cavities of the leaf, thereby, increasing
transpiration. This is what took place in the above example. Light also causes the
stomates to open, allowing transpiration. Transpiration effectively cools the