Carbon sequestration in trees and regrowth vegetation as affected by clearcut and partial cut harvesting in a second-growth boreal mixedwood

Abstract

Ecosystem biomass and C sequestration and cycling were measured in a mature, budworm-ravaged, second-growth boreal mixedwood stand subjected to clearcut and partial cut harvest treatments. Ninety permanent sample plots, distributed among fifteen 10 ha blocks, were established in 1993 and remeasured shortly after harvest and, again, 5 years later to ascertain C removals, as well as post-harvest ingrowth and upgrowth. In addition, litter bags and litter traps were installed and ground vegetation and forest floor samples were collected to monitor changes in ecosystem C pools and fluxes as affected by harvesting. The harvested blocks were quickly reoccupied by a thriving ground species regrowth, followed by a prolific trembling aspen thicket. Despite this, 5-year growth per area on control plots exceeded that on either partial cut or clearcut plots. Annual C assimilation rates in the post-harvest period were similarly significantly higher on control (3.1 Mg ha −1 per year) than on partial cut (1.8 Mg ha −1 per year) or clearcut (0.3 Mg ha −1 per year) plots. When growth was expressed as a function of biomass, the order reversed indicating the young growth to be the more vigorous. The forest floor lost little mass during the post-harvest period. Further, leaf litter decomposition was slower on clearcut plots than in uncut forest. Results suggest that ecosystem C pools and fluxes are rapidly reconstituted following harvest. If harvesting were to occur, ecosystem C assimilation in boreal mixedwood forest would be maximized under partial cutting.