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Natural disturbance and climate variability in the dry cool sub-boreal spruce ecosystem of the central interior of British Columbia Campbell, Kirstin Anne

Abstract

This research presents an evaluation of current sustainable forest management policies in British Columbia within the context of past, current and future disturbance regimes, and including the possibility of a changing climate, for a 1 million ha study area in the dry cool sub-boreal spruce ecosystem in the central interior of the province. In British Columbia, policy mandates that management should be consistent with the temporal patterns of natural disturbance processes. This research critically assesses such a policy from a number of perspectives, including an historical analysis, a modelling exercise of future conditions, and an examination of the relationship between climate and disturbances. Spatial disturbance data for fires and mountain pine beetle (1904-2004) were combined with vegetation data to create a comprehensive database of historical disturbances and landscape conditions in the study area; these data were used in all subsequent analyses. The historical and current range in variability in natural disturbances was characterized in order to make recommendations of refinements in BC's sustainable forest management policies. Compared to the time period 1904-1953, disturbance frequency was lower, return intervals were longer, and early seral stage forests have declined in more recent time periods (1954-2004). In most cases the current landscape does not meet the policy guidelines. There is a need, however, to make these policies species-specific rather than ecosystem-specific. A forest management model was used to examine the potential impact on the landscape of harvesting forests at the same rate as historical disturbances. Only after 130 years of such a harvesting or disturbance regime, did the landscape return to the historical range of variability in condition. The relationship between annual area disturbed and the Pacific Decadal Oscillation, temperature and precipitation) climate variables over an 89-year time period were modelled using Poisson regression. Although broad-scale variables such as temperature and precipitation were important, so was the multidecadal cycling of finer scale processes such as the Pacific Decadal Oscillation. The main conclusion of this dissertation is that any analysis of the historical range of variability in disturbances, especially if it is being used to guide management policy, must include the effects of climate on disturbances.

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