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Impact of partial harvesting on the net ecosystem production of a mixed conifer forest following mountain pine beetle attack Mathys, Amanda

Abstract

The recent mountain pine beetle (MPB) outbreak has had a major impact on the carbon (C) cycling of lodgepole pine forests in British Columbia. Mitigation efforts to control the insect outbreak have led to increased harvesting rates in the province. This study determines whether partial harvesting as an alternative forest management response to clearcutting can increase the net ecosystem production (NEP) of a mixed conifer forest (MPB-09) in Interior BC. Using the eddy-covariance (EC) technique, the C dynamics of the 70-year old stand were studied over the two years after partial harvest following MPB attack and also compared to an adjacent clearcut (MPB-09C) over the growing season. The annual NEP at MPB-09 increased from -107 g C m⁻² in 2010 to -57g C m⁻² in 2011. The increase of NEP was because the associated increase in annual gross ecosystem photosynthesis (GEP) from 812 g C m⁻² in 2010 to 954 g C m⁻² in 2011 exceeded the increase in annual respiration (Re) from 920 g C m⁻² to 1011 g C m⁻² in the two years of study. During the growing season of 2010, NEP at MPB-09C was -132 g C m⁻² indicating high C losses in the clearcut. MPB-09 was a C sink during the growing season of both years, increasing from 9 g C m⁻² in 2010 to 47 g C m⁻² in 2011. The increase of NEP in the partially harvested forest suggests stand recovery following harvest, which corresponds to a 25% increase in the maximum assimilation rate in the second year. This study shows that retaining the healthy residual forest can greatly enhance the C sequestration of MPB-attacked stands and has important implications for forest management.

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