ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

The soils on the study site have developed in glacial ti1 1. The surface organic
horizon in the forest, made up largely of decaying pine needles and twigs, is 2 to
3 cm thick. Below this, the surface mineral soil typically is loam with a platy
structure. This grades into sandy to gravelly loam, with coarse fragments (> 2 mm
in diameter) making up as much as half the volume below a depth of 112 m. The
soils classify as Mollic Cryoboralfs and Mollic Cryochrepts.* Many roots are found
in the upper 30 to 40 cm of mineral soil. Mottled and grey coloration, indicating
a lack of aeration and sometimes water saturated conditions, frequently are found
below depths of 1 m.
METHODS
Four units of approximately 8 hectares (20 ac) each were selected for clear-
cutting in 1971 (fig. 2). Two units were harvested using methods conventional in
this region--trees were felled, limbed, cut to a 15 cm diameter top, and then tree-
length skidded to landings with crawler tractors. The other two units were harvested
using a mechanical fell er-buncher; rubber-tired skidders hauled enti re trees to
landings, where the sawlogs were cut out and the remainder was chipped. All standing
1 ive and dead trees to 8 cm (about 3 in) in diameter, and a1 1 down logs to 15 cm
diameter, were removed from these two "near complete" units.
After harvest, each unit was divided into quarters and a1 ternative treatments
applied to the logging debris. On each of the conventionally logged areas the
debris was left as it fell for broadcast burning on two quadrants or piled with
dozer blades into windrows on the remaining two quadrants. These windrows, where
debris was concentrated on about 18 percent of the area, were burned a year later,
in the fall of 1972. The broadcast slash was burned in June 1973. The "near
complete" logged units were re1 atively free of coarse logging slash. The quadrants
on these were either left untouched, or were mulched with a layer of woodchips
equivalent in volume to the amount of nonmerchantable material that had been removed.
~ulchin~ with chips to an average depth of 10 cm was completed in the spring of
1973.
To study tree regeneration, the quadrants on a11 units were divided into
thirds. In June 1973, one-thirdkf each quadrant was planted to 2-0 lodgepole
pine, one-third was spot seeded to lodgepole pine, and one-third was left to
regenerate natural 1 y.
In addition to the four study units, a fifth, conventionally logged, nearby
unit was used for comparing soil solution chemistry under and between burned piles
of logging debris. This unit was clearcut in 1973 and piled and burned in summer
and autumn of 1974. Soil solution samplers were installed there in spring 1975.
Except for the fifth unit, data from the study area were gathered during five
growing seasons after completion of all treatments.
Five planted trees and five seeded trees were sacrificed from each quadrant of
each unit in 1977. Each tree was dissected into five components: (1) needles of
current year, (2) needles of prior years, (3) terminals of current year, (4)
remainder of above-ground portion of tree, and (5) roots. These were oven-dried
and weighed, then analyzed quantitatively for contents of nitrogen , phosphorus,
potassium, calcium, magnesium, sodium, zinc, iron, ash, and, in the case of planted
stock only, boron. Similar, but less detailed, sampling and analyses of lodgepole
pine regeneration were made in 1975, after three growing seasons. All chemical
2Personal communication with A. R. Southard, Utah State Univ., Logan.