Litterfall in the Clearcut Site at Harvard Forest 2012

Clearcutting a forest ecosystem can result in a drastic reduction of the stand’s
productivity. Despite the severity of this disturbance type, past studies have found that the
productivity of young regenerating stands can quickly rebound, approaching that of mature
undisturbed stands within a few years. One of the obvious reasons is increased leaf area with
each year of recovery. However, a less obvious reason may be the variability in species
composition and distribution during the natural regeneration process. The purpose of this study
was to investigate to what extent the increase in GEP, observed during the first four years of
recovery, in a naturally regenerating clearcut stand was due to 1) an overall expansion of leaf
area, and 2) an increase in the canopy’s photosynthetic capacity stemming from either species
compositional shifts or drift in physiological traits within species. We found that the
multi-year rise in GEP following harvest was clearly attributed to the expansion of leaf area
rather than a change in vegetation composition. Sizeable changes in relative abundance of
species were masked by remarkably similar leaf physiological attributes for a range of
vegetation types present in this early successional environment. Comparison of upscaled
leaf-chamber to eddy-covariance-based light-response curves revealed broad consistency in both
maximum photosynthetic capacity and quantum yield efficiency. The approaches presented here
illustrate how chamber- and ecosystem-scale measurements of gas exchange can be blended with
species-level leaf area data to draw conclusive inferences about changes in ecosystem processes
over time in a highly dynamic environment.