Climate variability and management impacts on carbon uptake in a temperate pine forest in Eastern Canada using flux data from 2003 to 2013

Abstract:

Temperate forests play an important role in global carbon cycle. In this study, we evaluate the impacts of climate variability and management regime on carbon uptake in a 75-year old temperate pine (Pinus strobus L.) forest, near Lake Erie in southern Ontario, Canada using eleven years (2003 to 2013) of eddy covariance flux data. These fluxes are compared with similar measurements made in an 80-year-old deciduous (Carolinian) forest, established in 2012. Both forests are managed stands and part of the Turkey Point Flux Station and global Fluxnet. Mean net ecosystem productivity, NEP, in the conifer stand is 145 (range 35 to 277) g C m² y^-1 over the 2003 to 2013 period, while mean NEP in the deciduous stand is 271 (226 and 317) g C m² y^-1 from 2012 to 2013. The study period experienced four distinct extreme weather patterns: warm and dry springs in 2005 and 2012, extremely wet and warm summer in 2006, a summer drought in 2007 and warm summers in 2010 and 2012. In February-March 2012, the conifer stand was selectively thinned and approximately 30% of trees were removed to improve light and water availability and stimulate growth of remaining trees. Thinning reduced NEP in the first post-thinning year, with mean annual NEP of 48 g C m² y^-1 in 2012. Increased supply of dead organic matter and warm temperatures in 2012 increased ecosystem respiration much more than photosynthesis, resulting in lower annual NEP. Heat stress and drought in spring of 2005 reduced NEP of the conifer stand to 35 g C m² y^-1. The impact of this extreme weather event on NEP was similar to that observed in 2012 when the stand experienced a drastic structural change, a dry spring and warm temperatures throughout the growing season. Observed fluxes from this forest and other Fluxnet sites were used to develop and validate a C and N coupled dynamic vegetation model, CLASS-CTEM-N that was applied to simulate terrestrial ecosystem’s carbon, water and energy budgets at 0.5 x 0.5 degree spatial resolution across the globe from 1901 to 2010 as part of North American Carbon Program (NACP) site-level and model intercomparison initiatives. The inclusion of the N processes in CLASS-CTEM model has improved model response to changing climate and atmospheric CO₂ concentration levels.