Carbon balance of a partially harvested mixed conifer forest following mountain pine beetle attack and its comparison to a clear-cut

A Mathys,A L Fredeen,G Nishio,N J Grant,R S Jassal,P J Burton,D L Spittlehouse,Z Nesic,M Brown,J A Trofymow,T A Black,R Bowler,G Meyer

doi:10.5194/bg-10-5451-2013

Abstract

Abstract. The recent mountain pine beetle (MPB) outbreak has had an impact on the carbon (C) cycling of lodgepole pine forests in British Columbia. This study examines how partial harvesting as a forest management response to MPB infestation affects the net ecosystem production (NEP) of a mixed conifer forest (MPB-09) in Interior BC. MPB-09 is a 70-year-old stand that was partially harvested in 2009 after it had been attacked by MPB. Using the eddy-covariance technique, the C dynamics of the stand were studied over two years and compared to an adjacent clear-cut (MPB-09C) over the summertime. The annual NEP at MPB-09 increased from −108 g C m−2 in 2010 to −57 g C m−2 in 2011. The increase of NEP was due to 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, exceeding the increase in annual respiration (Re) from 920 g C m−2 to 1011 g C m−2 during the two years. During the four month period between June and September 2010, NEP at MPB-09C was −103 g C m−2, indicating high C losses in the clear-cut. 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 stand amounted to a recovery corresponding to a 26% increase in the maximum assimilation rate in the second year. This study shows that retaining the healthy residual forest can result in higher C sequestration of MPB-attacked stands compared to clear-cut harvesting.

Highlights

Solid EarthForest management practices in response to insect outbreaks have an impact on the forest carbon (C) balance
Measurements at mountain pine beetle (MPB)-09 showed that 2010 was a warmer and drier year with a mean annual Ta of 4.9 ◦C compared to 3.0 ◦C in 2011 (Fig. 2; Table 2)
This study examined the effects of partial and clear-cut harvesting on the C balance of a sub-boreal forest that was previously attacked by the MPB

Summary

Introduction

Forest management practices in response to insect outbreaks have an impact on the forest carbon (C) balance. Columbia (BC) the mountain pine beetle (MPB) outbreak began in the late 1990s and has affected a total area of minitlolioAnlbheartoaf(Bpi.nTCe.-hlMeeaidnCiinstgrryystooafnsdFpsorhweseittshr,eaLarnecdesnatnedxpNaant--. The unprecedented scale of the outbreak has killed 710 million m3 or 53 % of the merchantable pine volume in BC from 1999 to 2011 (Walton, 2012). Reasons for the expansion of the outbreak include climate change, which has been attributed to increasing atmospheric concentrations of carbon dioxide (CO2) and other greenhouse gases on a global scale (IPCC, 2007). A. Mathys et al.: Carbon balance of a partially harvested mixed conifer forest

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