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

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.

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

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-yr 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 clearcut (MPB-09C) over the growing season. 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 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 stand amounted to a recovery corresponding to a 25% 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 clearcut harvesting.

Influence of spring and autumn phenological transitions on forest ecosystem productivity

We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an ‘extra’ day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixed-species stands.

Ecosystem carbon exchanges of a subtropical evergreen coniferous plantation subjected to seasonal drought, 2003–2007

The behavior of whole ecosystems in humid climate zone in response to drought is less well documented. Continuous measurements of carbon dioxide and water vapor exchange using the eddy covariance technique during 2003–2007 were made above a subtropical evergreen coniferous plantation in Southeast China. Seasonal distribution of precipitation and temperature was inconsistent during the summer, which resulted in droughts frequently. Gross ecosystem photosynthesis (GEP), ecosystem respiration (RE) and net ecosystem production (NEP) showed clear seasonality, with low rates during droughts and in winter. With statistical significance, the monthly GEP and RE increased exponentially with air temperature, but the monthly NEP was less sensitive and only increased linearly with air temperature. However, the function response of monthly NEP and its components (GEP and RE) disappeared under high temperature and low soil moisture. Monthly and yearly RE showed a statistically linear and positive dependence on the corresponding GEP. Annual NEP varied among years from 306 to 430 g C m−2 (mean 395, SD 50). Interannual variability in NEP was controlled primarily by air temperature and the ratio of precipitation and evapotranspiration that affected the RE/GEP ratio, which varied between 0.76 and 0.81 (mean 0.78, SD 0.02).

Ecosystem carbon exchange of a subtropical evergreen coniferous plantation subjected to seasonal drought, 2003–2007

The behavior of whole ecosystems in humid climate zone in response to drought is less well documented. Continuous measurements of carbon dioxide and water vapor exchange using the eddy covariance technique during 2003–2007 were made above a subtropical evergreen coniferous plantation in Southeast China. Seasonal distribution of precipitation and temperature was out of step during the summer, which resulted in droughts frequently. Gross ecosystem photosynthesis (GEP), ecosystem respiration (RE) and net ecosystem production (NEP) showed clear seasonality, with low rates during seasonal drought and in winter. The exponential response of monthly GEP and RE to air temperature provided us an implication that monthly NEP was less sensitive and only increased linearly. However, the function response of monthly NEP and its components (GEP and RE) disappeared under high temperature and low moisture. Monthly and year RE showed a linear and positive dependence on the corresponding GEP, with statistically significant. Annual NEP varied among years from 306 to 430 g C m−2 (mean 395, SD 50). Interannual variability in NEP was controlled primarily by air temperature and the ratio of precipitation and evapotranspiration that affected the RE/GEP ratio, which varied between 0.76 and 0.81 (mean 0.78, SD 0.02).