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Harvard Forest Symposium Abstract 2016
- Title: Long term trends and variability in carbon exchange at Harvard Forest EMS
- Primary Author: J. William Munger (Harvard University)
- Additional Authors: Evan Goldman (Harvard University)
- Abstract:
The Harvard Forest Environmental Measurements Site (HFEMS) tower was established in 1989. Continuous CO2 flux measurements that can be integrated to determine annual carbon exchange between forest and atmosphere have been made since 1992. In 1995 we established a set of 10m diameter plots along eight 500m transects radiating from the tower in the dominant upwind direction to sample the vegetation in the tower footprint. These have been resurveyed annually to quantify above ground woody increments, mid-summer foliar nitrogen, and species-specific litter inputs.
Throughout the last 2 decades the forest surrounding HFEMS has been accumulating carbon. Annual NEE increased from a mean value of about 2 Mg-C ha-1y-1 during the 1990’s up to a maximum of 6 Mg-C ha-1y-1 in 2008. NEE declined over the next two years, following an ice storm in 2008, and a particularly wet and cloudy spring in 2009 (Figure 1). Annual NEE has recovered since 2011. Above-ground wood growth generally follows annual NEE, though there is some evidence for a lag. AGWI continued to increase from 2005 onward until it dropped in 2011, while NEE showed a similar reduction the year before. Foliar nitrogen generally declined over the period 2010-2014, with a suggestion of recovery starting in summer of 2015 for the red oaks (Figure 2).
Figure 1 Annual Net Ecosystem Exchange (NEE – positive values indicate uptake by forest), above-ground woody increment (AGWI), and litter fall observed at the HFEMS flux tower and biometry plots from 1992 – 2015.
Figure 2 Foliar nitrogen content in samples collected during middle of growing season from upper canopy branches. - Research Category: Forest-Atmosphere Exchange
Large Experiments and Permanent Plot Studies - Figures: NEE_AGWI_litter.9214.png
fig.2015.png
