You are here

Harvard Forest >

Harvard Forest Symposium Abstract 2005

  • Title: Recovery of net ecosystem carbon sequestration following a shelterwood harvest at Howland Forest, Maine, USA
  • Primary Author: Neal Scott (Woods Hole Research Center)
  • Additional Authors: Bryan Dail (University of Maine); Eric Davidson (University of Maryland - Center for Environmental Science); David Hollinger (USDA Forest Service); Holly Hughes (Woods Hole Research Center); John Lee (University of Maine); Chuck Rodrigues (University of Maine)
  • Abstract:

    Forest management practices can have a large impact on rates of carbon sequestration in forest, yet little research has explored the magnitude and direction of these changes for different management practices. This is a critical issue in the northeastern USA, where a majority of forests are managed with varying degrees of intensity. Harvesting activities give rise to a short-term decline in leaf area and an increase in detritus on the forest floor, but whether this leads to a reduction in net carbon sequestration over time depends greatly on rates of individual tree growth after harvest and rates of residue decomposition. We are evaluating the impact of a commercial shelterwood harvest on forest carbon sequestration at Howland Forest in central Maine. A cut to length system with forwarding was used. Under this management system, one ~60-year rotation includes three harvests, each removing about one-third of the basal area. This type of management has increased dramatically throughout the region over the past decade.





    Harvesting removed about 15 Mg C/ha (SEM=2.1) (~30%) of live biomass, and created about 5.3 Mg C/ha (SEM=1.1) of aboveground and 5.2 Mg C/ha (SEM=0.7) of root/stump detritus. Leaf-area index and litterfall declined initially by about 40% with harvest. A comparison of half-hourly summer-time (August) net ecosystem exchange (NEE) between unharvested and harvested stands indicated about an 18% reduction in NEE one year after harvest. This resulted from both a decline in rates of carbon uptake, and a decline in respiration (Table 1). In 2004, three years after harvest, comparison of carbon uptake and respiration during the growing season suggests that daytime carbon uptake rates have recovered to almost pre-harvest levels, while increased respiration resulting from slash and detritus decay kept NEE lower than the control tower. Slash respiration rates correlated positively with both temperature and moisture, yet moisture content varied little during 2004 due to well-spaced rainfall events. Based on exponential models of slash decay, and an assumed reduction in carbon uptake rates by the trees in proportion to the reduction in basal area, we suggest that the harvested stand at Howland Forest should be storing about 0.6 Mg C ha-1 y-1.into vegetation (Figure 1, middle line). This agrees closely with measured annual C sequestration in 2004, which show the forest storing about 0.7 Mg C Mg C ha-1 y-1 (Figure 1). While annual NEE is still quite low in the harvested stand compared to the control stand (~2.5 Mg C ha-1 y-1) three years after harvest, our results suggest that carbon uptake and storage in the live vegetation during the growing season recovers quickly following a shelterwood harvest.





  • Research Category: