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Some effects of forest floor displacement on soil properties and lodgepole pine productivity in the Boundary Forest District

University of British Columbia

Forest floor displacement occurs during ground skidding and other forest harvesting and silvicultural operations. It includes excavation, scalping, mineral soil exposure, and burial of the forest floor. Two aspects of forest floor displacement can result in soil degradation and may impede forest regeneration; the redistribution and loss of nutrients, and the exposure of unfavourable rooting medium. Current soil conservation regulations, introduced by the new British Columbia Forest Practices Code, limit the amount of forest floor displacement that is acceptable during harvesting operations. However, the limits imposed by the Code are contentious, especially in Boundary Forest District, where the prevailing soil conditions are regarded as being particularly sensitive to forest floor displacement by some foresters and particularly tolerant of it by others. Evidence regarding the long-term biological sustainability of forest floor displacement is needed to confirm or amend the current restrictions on forest floor displacement. A retrospective study of the effects of forest floor displacement on lodgepole pine productivity was performed. Soils were surveyed for forest floor displacement atfive sites and samples were analyzed to assess the impact of forest floor displacement on soil nutritional properties. Foliar tissue samples were collected at four sites and analyzed to assess the nutritional impact of forest floor displacement on lodgepole pine trees. Growth of trees ranging in age from three to twenty seven-years-old was assessed at four sites and stem productivity was related to the amount of forest floor displacement present around each stem. Soil organic matter content, total N and total C are reduced by forest floor displacement, while available P increases and the C:N ratio decreases. Soil chemical analysis suggests that although forest floor displacement results in a reduction in total soil nutrient content, the nutrients present on scalped soils may be more available for root uptake. Changes in the above soil properties are shown to be temporary as soils appear to recover from forest floor displacement over time. Statistically significant differences in foliar nutrient concentration are infrequent among seedlings growing on scalped and control soils. The mean foliar concentrations of macronutrients are often slightly higher in scalp trees compared to control trees. Statistically significant differences in seedling productivity are also infrequent, and no permanent, negative impacts on lodgepole pine productivity related to forest floor displacement are indicated. Possible ancillary effects of forest floor displacement on regeneration and stocking density are discussed. Recommendations regarding some aspects of the forest floor displacement regulations and future study are given.

Thesis/Dissertation

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2009-03-24

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http://hdl.handle.net/2429/6392

Soil Science

University of British Columbia

UBCV

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