Net ecosystem productivity of temperate and boreal forests after clearcutting–a Fluxnet-Canada measurement and modelling synthesis

Abstract

Clearcutting strongly affects subsequent forest net ecosystem productivity (NEP). Hypotheses for ecological controls on NEP in the ecosystem model ecosys were tested with CO 2 fluxes measured by eddy covariance (EC) in three post-clearcut conifer chronosequences in different ecological zones across Canada. In the model, microbial colonization of postharvest fine and woody debris drove heterotrophic respiration ( R h ), and hence decomposition, microbial growth, N mineralization and asymbiotic N 2 fixation. These processes controlled root N uptake, and thereby CO 2 fixation in regrowing vegetation. Interactions among soil and plant processes allowed the model to simulate hourly CO 2 fluxes and annual NEP within the uncertainty of EC measurements from 2003 to 2007 over forest stands from 1 to 80 yr of age in all three chronosequences without site- or species-specific parameterization. The model was then used to study the impacts of increasing harvest removals on subsequent C stocks at one of the chronosequence sites. Model results indicated that increasing harvest removals would hasten recovery of NEP during the first 30 yr after clearcutting, but would reduce ecosystem C stocks by about 15% of the increased removals at the end of an 80-yr harvest cycle. DOI: 10.1111/j.1600-0889.2010.00500.x