ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

The silvicul tural treatments applied were clearcutting, she1 terwood, and group
selection cuts. Within each replicate of these were four levels of slash disposal:
1. slash left in place; 2. slash removed; 3. slash burned-low intensity burn; 4.
slash burned-medium-low intensity burn (Barger , this proceedings).
Abbott Creek is an intermittent creek which begins in the study area and then
goes below ground to emerge below the treated areas. None of the treatments appl ied
produced significant changes in stream water chemistry, and only minor increases in Na
content for a few days. These results are not definitive because of the peculiar
nature of the stream, but other studies have shown 1 ittl e stream pollution from log-
ging and light burns away from the riparian zone. The burns in this study had to be
done in unusually wet fall weather so that no significant nutrient losses occurred on
any of the treatments from fire.
Clearcutting represents the most severe case of nutrient removal from harvest.
Table 1 shows that under 0.25 percent of the total soil root zone nutrients were
removed in the boles as a result of clearcutting. Table 2 shows that harvest removes
under 15% of the immediately available nutrients except for Zn. The parent material
is low in Zn, and hence, available zinc is low. The removal of wood and bark takes
away low levels of all nutrients, but proportionally large amounts of zinc. This
would have no immediate impact on regeneration or seedling growth because the soil
still has its normal complement of available Zn and it will be at least 20 years
before the regeneration begins to make heavy demands on the soil for zinc. The zinc
in the wood and bark has accumulated there over 70 to 100 years at a slow rate. About
60% of that zinc left in heavy slash will be returned through decay in the next 70
years.
This study, along with others (Carlisle 1975) has shown that the nutrients removed
throuah the conventional harvest of wood and bark will be restored to the soil in 70
to 100 years through precipitation, even after clearcutting. The nutrient 1 eve1 s in
the precipitation at Coram are a bit higher than in other areas because of the ions
added to the atmosphere from a nearby aluminum plant.
If more fiber is removed beyond the usual level , the nutrient depletion could be
more serious, especially on a young, poor soil.
THE IMPACT OF FIRE AND LOGGING ON
NUTRIENT CYCLING AND SOIL DETERIORATION
If we have to resort to heavier utilization to provide fiber for supplementing
energy shortages through burning pelletized slash in generators for electricity or for
some other reasons, how much can we safely remove from the forest? How much nutrient
must be left to grow the next forest?
To answer these questions, we must first lay some ground rules. We cannot
accurately measure weathering rates, but we know that weathering is occurring. It
would seem unwise ecologically to depend on weathering to provide any portion of the
nutrients to grow the next forest. If we depend on the nutrients released from weath-
ering to grow the next forest, then the soil portion of "site" will never improve or
mature. Since we have largely young soils, we can anticipate gradual improvement in
the quality of these soils with each rotation if the nutrients released through weath-
ering are left behind when we harvest. Changes brought about by weathering will not
only improve nutrient availability for the next rotation, but will also increase the
water and nutrient storage capacities of the soil.