Harvard Forest >

Harvard Forest Symposium Abstract 2011

• Title: Carbon exchange of two New England forest stands & differential response to ice storm disturbance
• Primary Author: Kelly Morgan (Worcester State University)
• Additional Authors: Allison Dunn (Worcester State University)
• Abstract:

  In this study, we investigate the carbon balance of two differently-aged stands in Harvard Forest, and investigate their differential response to the 2008 ice storm. This study began in 2008 and consists of twelve plots across two separate study areas. 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 other study area ("harvest") is a nearby former red pine plantation that was 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 nearly 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 in 2008, 2009, and 2010; woody debris surveys in 2008 and 2010.
  
  
  
  Aboveground woody biomass was calculated using species-specific allometric equations. Both the control site and the 1990 harvest site had significant changes in aboveground carbon storage over the 2008-2010 study period. Aboveground carbon storage at the control site declined from 137.2 Mg C ha-1 in 2008 to 113.1 Mg C ha-1 in 2010, mostly due to mortality, but also due to a small amount of shrinkage in the aging red pines. The harvest site, in contrast, increased its aboveground carbon storage over the same time period (35.2 Mg C ha-1 to 41.6 Mg C ha-1). The significant (17%) loss in aboveground carbon storage at the control site is primarily attributable to mortality in the red pines, which had a large decrease in biomass (20%). All other species in the control site increased in biomass. In the harvest site, all tree species but one had a significant increase in biomass between 2008 and 2010, especially red oak (37%), beech (31%), paper birch (28%), and red maple (27%). The one species that did not increase in biomass was black cherry, which had significant mortality and lost 13% of its biomass since 2008. The large pulse of mortality in the red pines (control site) and black cherry (harvest site) is primarily attributable to damage from the ice storm that occurred in 2008.
  
  
  
  Woody debris biomass was calculated using the methods of Van Wagner (1968) and the decay-class specific bulk densities of Liu et al. (2007.) The 2008 ice storm had a significant impact on woody debris stocks at the red pine plantation, which increased from 6.8 Mg C ha-1 to 29.9 Mg C ha-1 between 2008 and 2010. This average mortality rate of 11.55 Mg C ha-1 y-1 significantly exceeded the long-term average of 0.6 Mg C ha-1 measured by Barford et al (2001) in a nearby 75-to-100-year-old stand at Harvard Forest. The harvest site, in contrast, experienced no ice storm-related enhancements to woody debris stocks, which slightly decreased from 5.8 Mg C ha-1 to 4.1 Mg C ha-1 between 2008 and 2010. The 2008-2010 inputs to the woody debris pool at the plantation (23.1 Mg C ha-1) far exceed the aboveground woody increment (1 Mg C ha-1 in shrinkage).
  
  
  
  Carbon exchange at these sites evidently depends on both stand age and disturbance history. The harvest site is clearly in a period of vigorous growth, sequestering an average of 3.25 Mg C ha-1 y-1. This is significantly higher than the average aboveground woody increment of 1.4 Mg C ha-1 measured by Barford et al. (2001) in a nearby 75-to-100-year-old stand at Harvard Forest. In contrast, the control site is in a period of decline, losing 0.5 Mg C ha-1 via slow shrinkage. Additionally, the large pulse of woody debris into the control site by the ice storm will affect ecosystem carbon exchange for decades as it decomposes. Respiration from the 2010 woody debris pool was estimated using the model of Liu et al. (2007) using decay-class specific decay constants. Carbon loss to the atmosphere from the ice-storm enhanced woody debris pool at the red pine plantation is significant, and will remain above 0.5 Mg C ha-1 through 2030. Both of these results indicate that this forest stand has shifted from a carbon sink to a carbon source, and that disturbance events such as ice storms serve as an accelerant to the process. The long-term legacy of this ice storm is significant; the carbon efflux, especially through 2020, is of a similar magnitude to that sequestered by a nearby 75-100-year old stand at Harvest Forest (1.0 – 4.7 Mg C ha-1 yr-1, Urbanski et al. 2007).
  
  

• Research Category: Forest-Atmosphere Exchange