Understanding forest carbon uptake and associated growth response is important for carbon sequestration and water management practices given the large quantities of carbon stored in forest ecosystems. Climate variability and forest management practices influence the magnitude and rate of soil CO2 efflux; however, their combined effects are complex and not well understood. This study investigated the response of soil CO2 efflux to the combined effects of climate variability, including those caused by climate oscillations, and shelterwood harvesting in a mature temperate white pine (Pinus strobes L.) forest, located near Lake Erie in southern Ontario, Canada. Analyses indicated that local winter temperatures and precipitation were influenced by climate oscillations, which affected forest carbon dynamics. After the shelterwood harvest removed approximately a third of the overstory canopy, no significant differences were found for soil temperature and soil moisture between the pre-harvesting (2008 to 2011) and post-harvesting (2012 to 2014) periods. Despite similar climate conditions pre- and post-harvesting, soil CO2 effluxes post-harvesting were lower. A Gaussian-Gamma specification model determined that heterotrophic (autotrophic) respiration decreased (increased) between pre- and post-harvesting, respectively. Mineral-soil respiration were similar pre- and post-harvesting. Soil CO2 efflux accounted for 78±9% of the annual ecosystem respiration (RE), derived using eddy-covariance fluxes. However, the overall net ecosystem productivity showed no significant difference between pre- and post-harvesting. This was attributed to an increase in the gross ecosystem productivity post-harvesting, compensating for the increased losses (i.e. increased RE). This study highlights the complexities of measuring various components of ecosystem respiration after a disturbance, such as a harvest. The knowledge gained from this study provides a better understanding of climate variability and shelterwood harvesting influences on ecosystem respiration and can be useful for forest managers focused on carbon sequestration and forest conservation. / Dissertation / Doctor of Science (PhD) / Coniferous forest plantations in eastern North America are undergoing silvicultural management to enhance their carbon sequestration capabilities and native-tree species diversity. This study investigated the combined influence of climate oscillations and shelterwood harvesting on soil carbon dynamics of a planted pine forest in southern Ontario, Canada. Between pre- and post-harvesting, soil temperature and soil moisture did not show any significant differences. However, soil CO2 effluxes in post-harvesting years were lower than pre-harvesting years. A Gaussian-Gamma specification model determined that heterotrophic (autotrophic) respiration decreased (increased) post-harvesting and mineral-soil respiration was similar between pre- and post-harvesting. An increase in ecosystem respiration post-harvesting, despite soil CO2 efflux decreasing and being the largest component, was primarily caused by the increase in autotrophic respiration due to enhancement in forest growth. This study improved the understanding of forest carbon dynamics by highlighting the importance of accounting for all components, which may contribute to ecosystem respiration. Results can be useful for forest management practitioners, specifically those focused on carbon sequestration and forest conservation.

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