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Harvard Forest Symposium Abstract 2008

  • Title: Effects of five years of soil warming on biogeochemistry at Barre Woods
  • Primary Author: Jennifer Johnson (Marine Biological Laboratory)
  • Additional Authors: Frank Bowles (Research Designs); Sarah Butler (Marine Biological Laboratory); Robert Hanifin (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Jacqueline Mohan (University of Georgia); Paul Steudler (Marine Biological Laboratory)
  • Abstract:

    Temperate-zone forests of the Northern Hemisphere are currently important sinks for atmospheric carbon dioxide. Whether or not they will continue to act as carbon sinks in a warmer world depends in large part on a complex set of plant and soil responses to global climate change. In a stand of mixed hardwoods at the Harvard Forest in central Massachusetts, USA, we have been studying some of these plant and soil responses in a large field experiment (30 x 30m plots) where soils have been heated 5°C above ambient. Over the first five years of the study, we observed two major ecosystem responses to soil warming that feed back to the climate system: a loss of carbon as carbon dioxide from soils, and an increase in the growth rate of trees that is leading to increased carbon storage in woody tissue. In response to heating, 1.1 metric tons C/ha/yr were released from the soil and 0.7 metric tons C/ha/yr were stored in the vegetation. Thus, since the start of the experiment, the equivalent of 70% of the carbon released from the soil has been stored in new woody growth. The increase in tree growth in response to warming appears to be related to both a lengthening of the growing season and an increase in the amount of soil nitrogen that becomes available to the trees each year. We hypothesize that over the next decade, the stimulation of carbon losses from soils by warming will cease, while the redistribution of nitrogen induced by warming will continue to stimulate carbon storage in the trees.

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