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Harvard Forest Symposium Abstract 2010

  • Title: Effects of soil warming on the carbon cycle at the Harvard Forest
  • Primary Author: Rose Smith (Marine Biological Laboratory)
  • Additional Authors: Andrew Burton (Michigan Technological University); Sarah Butler (Marine Biological Laboratory); Jennifer Johnson (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Jacqueline Mohan (University of Georgia); Jim Tang (Marine Biological Laboratory); Chelsea Vario (Dartmouth College); yumei zhou (Marine Biological Laboratory)
  • Abstract:

    A long term soil warming experiment at the Harvard Forest in central Massachusetts has given researchers insight into responses of northern temperate forests to changing climate conditions. The field experiment consists of two 30 x 30 m plots (control and heated) in a deciduous forest, where soil temperatures on the heated plot are maintained at 5°C above ambient. The experiment has been operating for eight years, including one year of pretreatment data collection. The large size of the plots has enabled the study of carbon cycling at the ecosystem level.

    In the first eight years of the experiment, warming caused an average net source of 940 kg CO2 ha-1 yr-1 from the ecosystem. This was driven mainly by increases in soil respiration which released an average of 1870 kg CO2 ha-1 yr-1. Warming also increased vegetation C storage causing a yearly average sink of 930 kg C ha-1 yr-1 which was equivalent to 50% of soil organic matter C loss. These results suggest that vegetation can significantly offset carbon loss from soil in a warming scenario. While the average carbon balance over 8 years has been a net source of CO2, the effect of soil warming on C storage has changed throughout the years. In the first seven years, warming was responsible for a net source of CO2 between 575 and 1770 kg CO2 ha-1 yr-1. In the eighth year, however, warming caused a net ecosystem carbon sink of 500 kg C ha-1. Microbial respiration spiked initially but has decreased over time in this experiment, while vegetation C storage has steadily increased. This trend is evidence that the carbon and nitrogen cycles in soil have been de-coupled; microbes have burned through the labile carbon pool, while trees continue to thrive on increased nitrogen availability and a slightly elongated growing season.

  • Research Category: Large Experiments and Permanent Plot Studies
    Soil Carbon and Nitrogen Dynamics