ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

ehavior. The design also provided means for comparing such behavior on logged
and unlogged forest land.
Except for a one-time measurement of soil particle-size distribution, all
soil and vegetal characteristics were measured on all plots each year. Bulk
densities of the 0-1 inch and 1-2 inch depths of the soil mantle were determined
from rep1 icated vol ume-weight soi 1 cores taken at random locations within the
plots. Total pore space was determined from tension-table measurements on the
soil bulk density cores. Soil particle size distribution was determined from
one-third of the composited bulk soil samples taken from the 0-1 inch and 1-2
inch depths of the soil mantle at random locations within each plot. Water-
stable aggregate distribution was determined from another one-third of the
cornposited bulk soil samples, and soil organic matter content was determined
from the remaining one-third. Vegetal characteristics, consisting of live
plant cover density, 1 i t ter cover density, logging debris cover density, rock
cover density, ash cover density, depth of chips, and size of bare soil
openings were measured with a point analyzer on 100 points established on
transects within each plot.
A rainfall simulator was used to apply water to each jnfiltrometer plot at
a constant rate of 3.26 inches per hour for 30 minutes. Runoff from trough
rain gages was collected at 5-minute intervals to provide a record of rainfall
amounts and intensities. Plot runoff, including both water and eroded soil,
was caught at 5-minute intervals and recorded. This discharge was retained as
part of the total runoff and eroded material from each plot.
LOGGING AND RESIDUE TREATMENT EFFECTS
Both the logging and residue disposal treatments significantly influenced
soil and vegetative characteristics and altered surface runoff and erosion
behavior.
BULK DENSITY
Effects on Soil Properties
The effects of residue treatments on bulk density of the surface 2-inches
of soil are shown in figure 1. The highest bulk density in 1973 occurred on
the blocks where chips were spread over the surface. These higher bulk den-
sities were caused by compaction from tractors used to spread the chips.
The next highest bulk densities occurred between windrows on blocks where
the logging residue was dozer piled and burned. These bulk densities also are
re1 ated to tractor compaction.
Four years later, in 1977, the highest bulk densities were between windrows
on blocks where the logging residue was dozer piled and burned. The lowest
bulk densities were found on control plots in unlogged areas adjacent to the
cl earcut tracts.
In general, between 1973 and 1977, soil bulk densities improved on the blocks
where chips were respread and also on the blocks where chips were picked up and
removed. In contrast, soil bulk densities on sites from which residue had been
removed by dozer pi 1 i ng fai 1 ed to recover or improve.