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Harvard Forest Symposium Abstract 2019

• Title: Carbon Budget of the Harvard Forest Long-Term Ecological Research Site: Pattern, Process and Response to Global Change
• Primary Author: Audrey Barker Plotkin (Harvard Forest)
• Additional Authors: John Aber (University of New Hampshire - Main Campus); Emery Boose (Harvard Forest); Eric Davidson (University of Maryland - Center for Environmental Science); Michael Dietze (Boston University); Aaron Ellison (Harvard University); Adrien Finzi (Boston University); David Foster (Harvard University); Serita Frey (University of New Hampshire - Main Campus); Marc-Andre Giasson (Boston University); Trevor Keenan (Harvard); Jerry Melillo (Marine Biological Laboratory); Knute Nadelhoffer (University of Michigan (all campuses)); Scott Ollinger (University of New Hampshire - Main Campus); David Orwig (Harvard Forest); Andrew Richardson (Northern Arizona University); Kathleen Savage (Woods Hole Research Center); Jim Tang (Marine Biological Laboratory); Jonathan Thompson (Harvard Forest); Christopher Williams (Clark University); Steven Wofsy (Harvard University)
• Abstract:

  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-year-old closed-canopy forests. These data
  answered six questions: (i) where and how much C is presently stored in
  dominant forest types; (ii) what are current rates of C accrual or loss;
  (iii) what biotic and abiotic factors contribute to variability in these rates;
  (iv) is climate change affecting the forest’s C cycle; (v) how do rates of C
  accrual from regrowth compare to C cycle modifications imposed by
  global change experiments; (vi) are C stocks and accrual rates at the
  Harvard Forest representative of the surrounding ecoregion? 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 750–970 g C
  m-2 yr-1; belowground NPP contributed 30–60% of the total. Inventory
  data suggest no 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 prior to
  infestation by the hemlock woolly adelgid (HWA) in 2013, and then
  became a net C source. Stand dynamics and climate change in the last
  three decades enhanced the C sink in hardwood stands; NPP increased
  26% between 2000–2014 (p = 0.02) and NEP increased 93% between
  1992–2015 (p = 0.13). The C sink in regrowing biomass equaled or
  exceeded C cycle modifications imposed by global change experiments.
  Median forest biomass in the surrounding ecoregion was only 78% of
  that at the Harvard Forest due to higher timber harvesting rates across
  the region. Data and 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 disturbance increases.

• Research Category: Soil Carbon and Nitrogen Dynamics
  Large Experiments and Permanent Plot Studies
  Forest-Atmosphere Exchange


• Figures:
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