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Effects of natural disturbance and harvesting on the landscape and stand level structure of wet, cold Engelmann Spruce-Subalpine Fir forests of south-central British Columbia, Canada Kopra, Kristin

Abstract

Engelmann Spruce-Subalpine Fir (ESSF) forests of interior British Columbia have increasingly become the target of forest harvesting in the past 40 years. Over the past decade, increasing public concern over maintaining biodiversity and ecological health within forests has brought about two primary pieces of legislation—The Forest Practices Code of 1995 and The Forest and Range Practices Act of 2002—that shape the current paradigm directing forest management. This paradigm maintains that biological diversity can be preserved by designing forest harvesting practices that result in regenerated forests that closely mimic naturally disturbed forests. It has been suggested that fire is the primary form of natural disturbance in ESSF forests. To date, there has been little knowledge gained about the natural disturbance patterns in ESSF forests, leaving forest managers with little guidance as to how to emulate these patterns. In this study, I sought to quantify both landscape-level and stand-level differences between naturally disturbed and harvested forests in the North Thompson variant of the wet, cold subzone of the ESSF (ESSFwc2) using the Geographical Information System Arcview and field measurement techniques. A decrease in the amount of old-growth forest as well as a decrease in the mean disturbance interval from naturally disturbed to harvested forests was found. Both patch size and patch size variability decreased with harvesting in older age classes and increased with harvesting in young age classes. A decrease in the amount of coarse woody debris and snags from naturally disturbed to harvested stands, as well as a significant difference in tree species composition between naturally disturbed and harvested stands was found. If emulation silviculture is the goal of forest management, this study concludes that the current harvesting method of clearcutting is failing to do so and, therefore, alternative harvesting methods and/or non-timber outputs should be considered.

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