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The carbon, water and energy balances of two lodgepole pine stands recovering from mountain pine beetle attack in British Columbia Brown, Mathew

Abstract

Over the past decade British Columbia (BC) has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy covariance (EC) technique to examine the impact of the MPB outbreak on the net ecosystem production (NEP) and evapotranspiration (E) of two lodgepole pine stands in the central interior of BC from 2007 to 2010. MPB-06, an 85-year-old stand, and MPB-03, a 110-year-old stand, were first attacked by the beetle in 2006 and 2003, respectively. EC measurements were also made in two harvested stands, one in 2005 and one in 1997 (CC-05 and CC-97, respectively) during the 2007 growing season. Annual NEP increased from -81 to 64 g carbon (C) m-² from 2007 to 2010 at MPB-06 due to an increase in gross ecosystem photosynthesis (Pg). At MPB-03, annual NEP also varied with Pg, ranging from -57 g C m-² in 2007 to 6 g C m-² in 2009. Annual ecosystem respiration (Re) did not vary greatly over the four years at both sites. At MPB-03, Pg was reduced by drought in 2009 and 2010. The increase in Pg at both sites was due to an increase in the photosynthetic capacity of the surviving trees and vegetation, as shown by foliar net-assimilation measurements. Light response analysis indicated that daytime Re values derived using nighttime NEP data were likely realistic estimates of the actual respiratory fluxes. NEP measurements at CC-97 and CC-05, showed that these stands are likely to remain C sources for as many as 10 years following harvesting. There was little interannual variation in E at both sites as the surviving trees and vegetation compensated for reductions in E due to the death of the overstory. Root-zone drainage was much greater at MPB-03 than at MPB-06, due to larger P at MPB-03. Growing season water deficit showed both stands to be water limited in spite of the high proportion of dead pine trees. Results from this study showed the importance of the remaining healthy trees and vegetation in the recovery of these stands from MPB attack.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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