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Harvard Forest Symposium Abstract 2015
- Title: Carbon sequestration dioxide in regenerating New England forests: quantifying pools, constraining fluxes, and characterizing response to disturbance
- Primary Author: Allison Dunn (Worcester State University)
- Abstract:
In this study, we investigate the long-term carbon balance of three differently-aged stands in Harvard Forest. This study began in 2008 and consists of eighteen plots across three separate study areas (Figure 1). One study area (Control) is the unharvested portion of plantation 25-H in the Prospect Hill Tract, which was planted in 1925 with red pine. The 2008 Harvest study area is directly adjacent to the control site and represents the portion of plantation 25-H that was harvested in 2008. The 1990 Harvest study area is a former red pine plantation harvested in 1990. Six 10-m radius circular plots were established at random locations in each of the study areas. All trees ≥ 5 cm diameter breast height (DBH; 1.3 m) were identified, measured, and tagged, totaling more than 800 trees across the 18 plots. Coarse and fine woody debris ≥ 2.5 cm diameter was surveyed using the line-intercept method along randomly oriented 10 m transects. DBH surveys were conducted yearly from 2008-2014; woody debris surveys were conducted in 2008, 2010, and 2014.
Our results show striking changes in forest structure and carbon sequestration since 2008. There has been a significant loss of aboveground woody biomass at the control site, from 137 Mg C ha-1 in 2008 to 109 Mg C ha-1 in 2014 (Figure 2). This was primarily driven by losses of approximately 33 Mg C ha-1 red pine, much of it during the 2008 ice storm (which generated ~9 Mg C ha-1 in that year alone.) As the overlying red pine canopy has thinned, the thickening understory now sequesters ~40% more carbon, increasing from 12.5 Mg C ha-1 in 2008 to 17.4 Mg C ha-1 in 2014. This can be seen in Figure 3, showing that trees with lower DBH values (understory) have increased their proportion of the stand at the same time as the larger red pine canopy trees have decreased.
In contrast, the 1990 Harvest site has steadily sequestered carbon during the entire study period, with its aboveground woody biomass rising from 35 Mg C ha-1 in 2008 to 47 Mg C ha-1 in 2014. There was little impact form the 2008 ice storm, with mortality the following year only 1.2 Mg C ha-1. The size class distribution of this young stand is widening and shifting larger (Figure 3) as the trees mature. We continue to monitor the growth of the 2008 harvest site, but as of yet its woody biomass remains too small in stature to be included in these calculations.
We plan to continue to monitor these three stands during the summer of 2015. We also plan to conduct a thorough inventory of standing dead wood at the control site to ensure accurate carbon accounting of the debris created by the 2008 ice storm. In cooperation with collaborators at UNH, we will resurvey the Chronic Nitrogen Amendment Study’s red pine control site to assess the representivity of our control site.
- Research Category: Forest-Atmosphere Exchange
- Figures: DunnAbstractFigs.pdf
