ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Moisture
Moisture is frequently identified as a major factor limiting the growth and
development of forest vegetation. Stem elongation and dry weight production can be
decreased at water potentials of -0.5 bar. And the growth rate of seed1 ings is often
substantially decreased at soil water potentials of -2 to -4 bars. It is not uncommon
to reach these levels in the upper layers of soil. Commonly reached lethal levels
can explain mortal ity of seed1 ings and sometimes mature plants. Large conifers have
been observed to split open as a result of drought (Hungerford 1973). Many good
articles discussing water deficits and plant growth are available (Kozlowski 1968a,
1968b, 1972, 1976, 1978; Slatyer 1967). Newmann (1980) and Packer (1980) discuss the
specific site effects of water deficits.
Gases
Carbon dioxide is needed for photosynthesis and to produce dry matter. Although
we know its importance in maintaining forest vegetation, we know very little about
how COP 1 imits vegetation in forested systems. We also know very 1 ittle about how
forest activities such as timber harvesting influence levels of carbon dioxide. It
generally is assumed that the levels of carbon dioxide are adequate, and we know that
global suppl ies of carbon dioxide are increasing (Machta 1972).
Oxygen concentrations affect the respirqtion rates of organisms. Probably the
most significant alteration of oxygen and carbon dioxide levels in forests can occur
in soils. Various activities such as scarifying and skidding can either loosen the
soil or compact it, thus altering gaseous exchange with the environment, Corn action
reduces the exchange, which causes an accumulation of carbon dioxide and depe ! etion
of oxygen. The result is a decrease in microbial activity and possibly root growth
(Boll en 1974). Reduction in microbial activity can adversely affect the nutrient
capital of the site. Residues or residue treatments that impede aeration or cause
surface compaction will a1 ter biological activity. A detailed discussion of such
relationships is beyond the scope of this paper. Bolin (1970) discusses the carbon
cycle and vegetative re1 ationships; Harvey (1 980) and Larsen (1 980) discuss microbiql
re1 ationships; and Jurgensen (1 980) discusses nitrogen re1 ati\onships.
Wind
Wind speed and direction affect biological systems in many ways, Since some
species are more susceptible to windthrow because of rooting habits, harvesting
prescrtptions must take local situations into account. If one relies on natural
regeneration for restocking, wind becomes an important factor in determining the
proper size and method of cutting. Since species differences exist, wind cqn hqve
differential effects.
Wind energy, particularly at high elevations and near coastal areas is also a
factor in distributing species and damaging vegetation. Wind-carried particles of
sand, etc., kill seedlings, Salt spray from ocean winds also causes damage. Constant
strong winds, such as at high elevations, cause deformities.