The effects of skid roads on soil physical and chemical properties, tree nutrition, and tree growth were studied at two steep sites with coarse-textured soils in the Interior Cedar-Hemlock zone east of Vernon, B.C. The study began in 1986 and continued for 11 years. Approximately one-third of each of the steep slope study areas was occupied by soil disturbances associated with construction and use of bladed skid roads. Treatment plots were established on five locations associated with skid roads: above and below the road, the inner and outer track of the road's running surface, and the skid road sidecast. Soil properties were measured before plantation establishment and during the first year of growth, and to a limited extent, after 10 years of growth. Seedling growth was measured at intervals between 1 and 10 years after establishment.
Whole soil bulk densities were increased by approximately 40% on the skid road surfaces. These bulk density increases were still apparent after 10 years. Although large relative increases were also evident in fine soil bulk densities, these bulk densities did not approach growth-limiting thresholds, except on the inner track at one site. Other soil physical properties, such as porosity, aeration, and water storage capacity were not reduced to below apparent threshold values. Soil moisture contents through the first growing season did not help to explain differences in the rates of tree growth. Although soil chemical content was reduced by displacement of the forest floor and surface mineral soil, soil chemical concentrations that remain may be sufficient to adequately support tree growth.
Tree growth over the 10-year period was best on the skid road sidecast and outer trail positions at both sites. Inner track growth was comparable to that of the non-track areas. Foliar nutrients did not indicate any possible deficiencies specific to the disturbed areas.
In these moist to wet ecosystems, the early growth of trees on the skid roads constructed on these very coarse-textured soils is enhanced relative to the undisturbed areas. However, the results should not be generalized and extrapolated to soils and ecological conditions outside those of the study areas. Ongoing mass wasting associated with the constructed skid roads may be reducing overall site productivity.
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Updated October 24, 2008