ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Per unit of depth, there was almost twice as much nitrogen in the surface 5 cm
of mineral soil than in the next 5-15 cm layer.
Organic matter content
The content of organic matter in the surface 5 cm of the undisturbed forest
soil ranged between 5 and 6 percent. In the 5-15 cm layer it declined to half this
concentration. The organic fraction of the surface 5 cm under each of the treatments
were:
Forest 6.0 5.2
Broadcast burned 7.2 5.9
Pi 1 ed- burned (under) 6.9 4.1
Pi 1 ed- burned (between) 7.1 4.6
Chi pped-removed 6.6 5.9
Chi pped-returned 7.1 8.6
Logging, broke up the fine organic debris in the A. horizon and incorporated
it into the mineral soil beneath, likely causing the initial increase in organic
matter content in 1972-1973. Burning and decomposition of this increment (and of
the residual organic material in the surface 5 cm) no doubt produced the decline
shown in 1977 on most treatments. During this timespan new plant growth added
little organic matter to the soil on these clearcut sites; hence, the decrease could
be expected.
Available nutrients
Table 5 shows the amounts of available nutrient elements (except sodium)
extracted from the 1977 soil samples. Total extractable sodium was the same for a1 1
sites--approximately 0.1 meq per 100 g of soil at both depths.
Available phosphorus was almost twice as abundant in the surface soils 5 years
after logging than it was in the undisturbed forest. The largest quantity was found
under chip mulch, followed by the soil under burned piles. In contrast, the soils
between burned piles did not differ significantly from those of the forest.
Table 5 expresses potassium, calcium, and magnesium cations in the form of
mill iequivalent weights of the total extractable amounts per 100 g of soil. The
total extractable amount is the sum of the exchangeable content plus the water
soluble content. Exchangeable cations comprised 90 percent or more of the total
extractable cations in these soils.
Extractable potassium was greatest in 1977 at both depths under the burned
piles of debris. Otherwise, the amounts of this element did not differ significantly
among treatments. There was about 20 percent more potassium in the surface 5 cm of
soil than in the 5-15 cm depth.
Logging increased slightly the amounts of extractable calcium in soils. In
1977 the surface 5 cm of soil under the burned piles contained almost twice the
calcium concentration of the undisturbed forest, this amount--14.6 meq per 100 g--
was significantly greater than all others. The highest amount of calcium in the
next 10 cm layer also were found under this treatment. Levels of extractable
magnesium, a similar divalent cation, followed the same pattern. There was only