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Open Access Publications from the University of California

Carbon budget of the Harvard Forest Long-Term Ecological Research site: pattern, process, and response to global change

  • Author(s): Finzi, AC;
  • Giasson, MA;
  • Barker Plotkin, AA;
  • Aber, JD;
  • Boose, ER;
  • Davidson, EA;
  • Dietze, MC;
  • Ellison, AM;
  • Frey, SD;
  • Goldman, E;
  • Keenan, TF;
  • Melillo, JM;
  • Munger, JW;
  • Nadelhoffer, KJ;
  • Ollinger, SV;
  • Orwig, DA;
  • Pederson, N;
  • Richardson, AD;
  • Savage, K;
  • Tang, J;
  • Thompson, JR;
  • Williams, CA;
  • Wofsy, SC;
  • Zhou, Z;
  • Foster, DR
  • et al.

Published Web Location

How, where, and why carbon (C) moves into and out of an ecosystem through time are long-standing questions in biogeochemistry. Here, we bring together hundreds of thousands of C-cycle observations at the Harvard Forest in central Massachusetts, USA, a mid-latitude landscape dominated by 80–120-yr-old closed-canopy forests. These data answered four questions: (1) where and how much C is presently stored in dominant forest types; (2) what are current rates of C accrual and loss; (3) what biotic and abiotic factors contribute to variability in these rates; and (4) how has climate change affected the forest’s C cycle? Harvard Forest is an active C sink resulting from forest regrowth following land abandonment. Soil and tree biomass comprise nearly equal portions of existing C stocks. Net primary production (NPP) averaged 680–750 g C·m−2·yr−1; belowground NPP contributed 38–47% of the total, but with large uncertainty. Mineral soil C measured in the same inventory plots in 1992 and 2013 was too heterogeneous to detect change in soil-C pools; however, radiocarbon data suggest a small but persistent sink of 10–30 g C·m−2·yr−1. Net ecosystem production (NEP) in hardwood stands averaged ~300 g C·m−2·yr−1. NEP in hemlock-dominated forests averaged ~450 g C·m−2·yr−1 until infestation by the hemlock woolly adelgid turned these stands into a net C source. Since 2000, NPP has increased by 26%. For the period 1992–2015, NEP increased 93%. The increase in mean annual temperature and growing season length alone accounted for ~30% of the increase in productivity. Interannual variations in GPP and NEP were also correlated with increases in red oak biomass, forest leaf area, and canopy-scale light-use efficiency. Compared to long-term global change experiments at the Harvard Forest, the C sink in regrowing biomass equaled or exceeded C cycle modifications imposed by soil warming, N saturation, and hemlock removal. Results of this synthesis and comparison to simulation models suggest that forests across the region are likely to accrue C for decades to come but may be disrupted if the frequency or severity of biotic and abiotic disturbances increases.

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