Abstract:
This study evaluated the recovery of compacted soils on logging
skid trails in clearcuts of the western Cascade Mountains of Oregon.
Soil types included clay, clay loam, silt loam, loam, sandy loam
and loamy sands. Sites ranged in age from five to 38 years since
harvest and 370 to llOOm in elevation. Soil bulk density, measured
with a nuclear density probe, was used to characterize compacted
soil conditions. A number of soil, vegetation and site variables
were studied to determine possible cause and effect relationships
with compaction recovery.
Study design consisted of nine sites with nine plots at each
site. Plots were classed by level of use with three plots in each of
the low, medium and high use level classes. At each plot, measurements
of bulk density were taken at the skid trail center, skid trail track and the less-disturbed area adjacent to the skid trail.
Determination of vegetative cover was also made at these locations.
Depths of measurement for bulk density were 5.1cm, 15.2cm and 30.5cm.
No statistical difference of bulk density values was detected
between skid trail use-level classes. A similar result was found
for the vegetative cover variables. Bulk density values on the
skid trail center and skid trail track were statistically similar.
However, density on the skid trail track (and center) were greater
than those of the less-disturbed area ([alpha]= 0.05). When the data
were stratified by site age, the skid trail track still retained
greater bulk densities than the less-disturbed area on the 38 year
old site. No trends in bulk density changes were observed over
time.
Interaction between herbaceous cover and overstory cover
decreased the usefulness of these variables for correlation with
recovery. However, shrubs indicated a reduction of percent cover
on skid trails up to 21 years since harvest, but not after
that time. This was the only variable measured which indicated
possible skid trail recovery.
Regression analysis was performed using the bulk density
difference between the skid trail track and less-disturbed area as
the dependent variable and several soil, site and vegetative variables
as independents. Multicolinearity among the independent variables
was high and when coupled with the variable nature of the bulk
density data, produced inconsistent results.
