ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

the soil will retain its ability to support tree growth. If organic matter is des-
troyed, the productivity associated with it also is destroyed until restoration
occurs. In instances where organic matter in the form of pathogen infested residues
is responsible for the spread of disease, organic matter removal and the resulting
loss of N or of ectomycorrhizal activity may be the best choice for production of
susceptible conifers. In other words, in an active root disease center, the losses
from root decay are likely to exceed any potential gain from leaving the infested
residues on the site if a susceptible species is the major component of the stand.
Where possible, conversion to disease tolerant species would be the preferred method
of dealing with pathogen-infested residues if organic matter is in short supply.
POTENTIAL HARVEST-RELATED IMPACTS ON SOIL QUALITY
Since ectomycorrhizal activity and non-symbiotic N-fixation rates vary directly
with forest site productivity (temperature-moisture) , and are somewhat predictable
within soil components, the importance of these components to conifer growth can be
estimated. If we assume microbial activities provide direct support to the growth of
a stand, as appears to be the case, then one can estimate the cost or beneflt , i n
terms of percent of growth change, from manipulating quantities or types of soil
organic matter on a giyen site. Our present data base provides an appropri>ate
exampl e .
Figure 1 outlines trends in ectomycorrhizal activity within the wood and humus
of three forest stands with adequate organic matter. Although the data are not
equivalent to a regression, they are indicative of we1 1 founded statistical changes
that can be expected. If, for instance, we were considering application of intensive
fiber utilization practices to these three sites, it is evident that the greatest
potential for negative impact would exist on the Douglas-fi r/ninebark habitqt type.
The figure indicates that up to about 38 percent of the seasonal growth on the
Doug1 as-fi r/ninebark site may be based on ectomycorrhizal activities supported by
soil wood. Therefore, if we removed the source of soil wood, there would be a
potential for reducing growth from the time the existing wood was dispersed Sn the
soil until new wood could be produced, decayed and reincorporated into the soil.
Turnaround time for such processes approximates 150 to 200 years (fig. 2). If it
takes 100 years to disperse the existing soil wood, then there would be a period of
50 to 100 years during which the growth potential of that site would be reduced.
Additionally, there would be a period of time during which a lesser reduction in
growth, proportionate to the gradual loss or restoration of soil wood, would occur.