Impact of variable retention harvesting on carbon sequestration in a red pine plantation in southern Ontario
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Forest management options aimed at mitigating the rate of increase in atmospheric concentrations of CO2, include thinning and partial harvesting to increase growth and carbon (C) capture of residual trees as a stand matures. Variable retention harvesting (VRH) can be used to increase forest growth rates and C sequestration, while enhancing biodiversity and resilience. Across southern Ontario, Canada, numerous plantations were established in the early 20th century on abandoned agricultural lands to stabilize soils, restore forest habitat, and produce wood products. Red pine (Pinus resinosa Ait.) was often planted because it grows rapidly and tolerates a variety of soil types. An 88-year-old red pine plantation was sampled to examine tree and stand level growth responses to different VRH treatments during a five-year pre- (2009–2013) and post-harvest (2014–2018) period. The treatments included: 33% and 55% aggregate retention, 33% and 55% dispersed retention, and an unharvested control. Stem radial growth and annual C increment were calculated for individual trees and at the stand level. At the tree level, growth and C increment increased under a dispersed retention pattern, regardless of the percentage of trees retained. At the stand level, total C increment was greatest at the higher retention levels and did not vary with retention pattern. The results suggest that retention level and pattern are important determinants of the mitigation potential of VRH. Where maximizing total stand C is a primary objective, higher retention levels should be considered. In comparison, a dispersed retention pattern can be used to maximize stem growth, C storage rate, and size of individual trees for use in long-lived wood products.