ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

I
about a fifth as much extractable magnesium in these soils as there was calcium,
however, despite the fact that the total amount of magnesium is twice that of
calcium. The concentrations of the extractable forms of both elements were a fourth
to a third greater in the surface 5 cm of mineral soil than they were below that
depth.
The amounts of available boron showed no particular pattern with respect to
treatments or depths. Boron concentration appeared to be slightly less in the
I deeper soi 1 1 ayer , however.
Zinc, in the 0-5 cm layer, was two to three times more concentrated under the
burned debris piles than on any other treatment, a highly significant difference.
Higher zinc concentrations, though not statistically significant, a1 so occurred on
the broadcast burned sites. Lesser concentrations of this element occurred in the
5-15 cm layer, a1 though the same pattern seemed to hold true.
Iron was significantly concentrated in both layers of soil under the chip
mulch--twice as concentrated as in the undisturbed forest. The next greatest
concentration occurred under the burned piles. Both soil layers had about equal
concentrations of this re1 atively abundant element.
Cation exchange capacity
The quantity of available metallic nutrients retained by soil depends upon the
soil's cation exchange capacity, which, in turn, depends upon the nature and amount
of clay and the amount of organic matter in the soil. Most of the cation exchange
capacity of these soils is in the clay fraction--a parameter not likely to be altered
much by the imposed treatments. The cation exchange capacity of the surface 5 cm
averaged 18.63 meq and that of the 5-15 cm layer averaged 15.27 meq per 100 g of
soil.
The four cations quantitatively analyzed in 1977 (potassium, sodium, calcium,
and magnesium) occupied a bit less than half the average exchange capacity in the
undisturbed forest, about half of this average under four of the treatments, and
nearly three-fourths of it under the burned piles.
Soil Solutions
From 1972 through 1977 mare than 600 samples of soil solutions from 44 tubes
under the six treatments were analyzed. The average concentrations of each element
for this period are summarized in table 6. Not all treatments were in effect for
this entire time. Only two treatments--forest and chipped-removed--produced records
for all 6 years; piled-burned (under) data cover 3 years; conventional clearcut only
1 year; all others produced 5 years of data.
Potassium concentrations increased under the chip mulch and under both burning
treatments (broadcast and beneath pi1 es) . This increase was most permanent, 1 asting
up to 5 years, under the chip mulch, whereas the effects diminished rapidly after 2
years under the broadcast burn. Sodium increases due to treatment were greatest
beneath burned pi 1 es.
Slightly higher concentrations of magnesium were observed on the treated sites,
especially under chipped-returned and the burns. The duration of these effects was
similar to that of potassium. Calcium levels increased and persisted under a1 1
treatments. Clearcutting alone appeared to be the primary cause for the increase of
both calcium and magnesium, with the chip mulch and the ash concentration under
burned pi1 es contributing additional amounts under these two treatments.