http://cfs.nrcan.gc.ca/authors/read/22242?format=title&lang=en_CA Publications by V.N. Foord en-ca 2012-03-05 16:12:33 MST 2012-03-05 16:12:33 MST webmaster@nofc.cfs.nrcan.gc.ca http://cfs.nrcan.gc.ca/publications?id=33347 Disturbances play an important role in determining the C balance of North American forests. This study used the eddy covariance (EC) technique to examine the impact of mountain pine beetle (MPB) (<em>Dendroctonus ponderosae</em>) outbreak on the gross ecosystem photosynthesis (P_g), ecosystem respiration (R_e) and net ecosystem production (NEP), of two lodgepole pine-dominated stands in the central interior of British Columbia. MPB-06, an 85-year-old stand, was first attacked in 2006 and by 2010 only ∼16% of the trees remained healthy. MPB-03, a 110-year-old stand with a developed secondary structure (tree seedlings and saplings, sub-canopy and canopy trees that survive the attack), was first attacked in 2003 and by 2007 had >95% pine canopy mortality. Annual NEP increased each year at MPB-06, from −81 g C m^-2 in 2007 to 64 g C m^-2 in 2010, due to an increase in P_g from 440 g C m^-2 in 2007 to 576 g C m^-2 in 2010. Annual R_e was more conservative, −ranging from 512 g C m^-2 in 2010 to 557 g C m^-2 in 2008. At MPB-03, NEP increased from −57 g C m^-2 in 2007 to 3 and 6 g C m^-2 in 2008 and 2009 before falling to −26 g C m^-2 in 2010. Between 2007 and 2010, P_g and R_e ranged from 430 to 516 g C m^-2 and from 487 to 513 g C m^-2, respectively. Variation in NEP at both sites was mainly a result of changes in P_g. At MPB-03, P_g was reduced by drought during the 2009 and 2010 growing seasons. An empirical logistic equation best described the relationship between R_e and soil temperature at 5-cm depth (T_s), and the relationship varied significantly over the four years at both sites. At both sites, over the 4 years the ratio of the growing season totals of modelled R_e using nighttime and daytime NEP data was well within 15% with the exception of 2010 at MPB-06. Growing season averages of foliar net assimilation followed a similar trend as average growing season P_g, increasing from 2007 to 2009 at MPB-06, and decreasing in response to drought in 2009 and 2010 at MPB-03. Growing season water use efficiency (P_g/evapotranspiration) increased from 2.2 to 2.8 g C (kg H₂O)^-1 from 2007 to 2010 at MPB-06, and ranged from 1.7 to 2.0 g C (kg H₂O)^-1 between 2007 and 2010 at MPB-03. Spring NEP was an important determinant of the annual C balance at both sites. Mon, 05 Mar 2012 http://cfs.nrcan.gc.ca/publications?id=33347 http://cfs.nrcan.gc.ca/publications?id=31532 British Columbia (BC), Canada is experiencing a severe mountain pine beetle (MPB) (Dendroctonus ponderosae) epidemic extending over an area of 135,000 km2. The widespread mortality of lodgepole pine (Pinus contorta var. latifolia) caused by the beetle has significant implications for BC's timber supply and Canada's carbon (C) budget. This study used the eddy-covariance technique to examine how the beetle is impacting the net ecosystem production (NEP) of two attacked lodgepole pine-dominated stands in the central interior of BC. MPB-06 is an 83-year-old stand that was first attacked in 2006. At the start of 2007 roughly 60% of the canopy had been attacked and by October 2008 only 21% of the trees remained healthy. MPB-03, a 110-year-old stand, had >95% pine canopy mortality as a result of a 2003 beetle attack, and also differed from MPB-06 in that it had a more developed secondary structure (consisting of tree seedlings and saplings and sub-canopy and canopy trees) that survived the beetle attack. Eddy-covariance measurements were also conducted in two stands near MPB-06 harvested in 2005 and 1997 (CC-05 and CC-97) for approximately three-week periods each during the 2007 growing season. MPB-06 had an annual NEP of -82 and -33 g C m-2, while MPB-03 had an NEP of -56 and 4 g C m-2 in 2007 and 2008, respectively. In the 2007 and 2008 growing seasons (May–September), MPB-06 was a sink of 12 and 52 g C m-2, while MPB-03 was a sink of 17 and 68 g C m-2, respectively. The productivity at MPB-06 resulted from an increase in photosynthesis by the remaining healthy trees and understory vegetation, while at MPB-03 the secondary structure and understory vegetation showed a strong capacity to sequester C due to an opening up of the stand as a result of canopy mortality. Average daily values of NEP during the measurement periods at CC-97 and CC-05 were -0.37 and -0.87 g C m-2, respectively, showing that even 10 years following harvesting, these stands are likely to remain growing season C sources. That MPB-06 and MPB-03 were growing season C sinks suggests that deferring the harvest of stands with significant levels of secondary structure could prevent MPB-attacked forested areas from becoming C sources over extended periods. Thu, 08 Apr 2010 http://cfs.nrcan.gc.ca/publications?id=31532