Moving towards carbon neutrality: CO2 exchange of a black spruce forest ecosystem during the first 10 years of recovery after harvest

Abstract

Disturbances control the landscape-level C dynamics of boreal forests, but post-disturbance C dynamics are usually poorly quantified. In the current study, we use 10 years of CO₂ flux measurements at a boreal black spruce ( Picea mariana (Mill.) B.S.P.) cutover in eastern Canada to estimate time to C neutrality, quantify the relative role of respiration versus photosynthesis during recovery, and determine the agreement between cumulated CO₂ fluxes and plot-level changes in C content. The site was a net source of 139 g C·m^–2·year^–1 2 years post-harvest, dropped further to a source of 173 g C·m^–2·year^–1 4 years post-harvest, following a scarification treatment, and was nearly C neutral 10 years post-harvest. Gross ecosystem productivity (GEP) increased by 50 g C·m^–2·year^–1 post-scarification, while ecosystem respiration (ER) increased by only 23 g C·m^–2·year^–1. The resulting net rate of increase of 27 g C·m^–2·year^–1 in net ecosystem productivity was driven by changes in increasing leaf area. In fact, vegetation regrowth had a much greater impact on annual fluxes than did interannual variability in climate. Biometric-based measurements of total C losses after harvest were in relatively good agreement with eddy-covariance-based estimates 8 years after the harvest.