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Impacts of partial harvesting on stand structure and wildlife habitat in the Prince George Forest Region Nishio, Grant Richard

Abstract

The present mountain pine beetle (MPB) epidemic is the largest forest insect infestation in Canada's history. The most common MPB management strategy involves clearcut harvesting large areas. However, i f all of the beetle-killed pine is removed with large clearcuts, the landscape will suffer dramatic reductions in wildlife habitat for many years. Alternatively, sometimes different types of partial harvesting are used that conserve some of the habitat values that would otherwise be removed with clearcutting. This study, done in the Prince George Forest Region, examines two types of partial harvesting I refer to as 'aggregate treatment' and 'dispersed treatment'. These treatments were not originally prescribed as true retention systems, but they are similar in design to aggregated and dispersed retention systems. The aggregate treatments retain small unharvested areas and the dispersed treatments retain individual dispersed trees (usually Douglas-fir veterans) throughout the cutblock. Two related studies were completed at the same site using the same data. The purpose of Study 1 was to determine how the abundance of several wildlife habitat variables differed between dispersed, aggregate, and unharvested control treatments. The purpose of Study 2 was to estimate the probabilities of windthrow and mortality according to tree, site, and neighbourhood factors. Tree size and species influenced windthrow occurrence, but as expected, windthrow was chiefly related to post-harvest exposure. Recommendations for future partial harvesting strategies must include consideration of the potential risk of windthrow. Large Douglas-fir trees have the lowest risk of windthrow and should be retained in dispersed treatments. Two or three time the desired number of trees should be retained in the dispersed treatments to compensate for the inevitable occurrence of windthrow. Aggregate patches should be at least one hectare in size to minimize windthrow damage. Lodgepole pine is at a high risk of MPB attack and non-pine species should therefore be retained in aggregates. It is also recommended to retain deciduous species in aggregates whenever possible since they have high wildlife value, but were relatively scarce in the study area.

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