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Natural regeneration on abandoned cutblock roads in the Okanagan Timber Supply Area McAllister, Daniel Allan

Abstract

Current knowledge of access structure site productivity is inadequate for determining whether these sites can support substantial tree growth. While many studies have examined tree growth on skidtrails and landings, their conclusions are based upon short-term results, and cannot be used to predict future stand growth. Several studies designed to assess the long-term effects of soil disturbance on tree growth are currently ongoing. This study looked retrospectively at disturbed sites within the Okanagan TSA in order to gain some understanding regarding the long-term effects of cutblock roads on forest site productivity. Productivity measures were employed to assess tree regeneration on traffic and non-traffic areas on roads that had been abandoned by traffic for at least 20 years. Adjacent non-roaded cutblock areas were used as controls. Study sites were established in six areas. Soils information, including bulk density, macroporosity, texture, coarse-fragment content, and organic matter content was collected from one study area. In total, over 80 traffic, non-traffic and control plots were established. The study found that the effects of cutblock roads varied significantly within the study areas among the study sites. There was no statistically significant reduction in site index of trees growing on areas where cutblock roads had been established. Traffic area stand densities, however, were found to have an overall average reduction of 70% when compared to control areas. Soil fine fraction bulk density on traffic road plots was found to be 36% greater than that of control plots. Non-traffic road plots had 16% higher fine fraction bulk density than controls. Macroporosity was reduced by 55% within traffic road plots, and by 38% within non-traffic road plots, when compared to control soil macroporosity. Within the traffic road plots, both site index and stand density were correlated with both soil bulk density and macroporosity. Plots with low site indices and low stand densities were associated with higher soil bulk density and low soil macroporosity. In addition, on traffic road plots, higher clay content was associated with low site index and low stand density. On traffic road plots, there was a correlation between site index and site tree age. This was not observed within either the non-traffic road plots or the control plots. This might be interpreted as a sign of site recovery being reflected in increased rates of tree growth.

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