Barre Woods Soil Warming Experiment at Harvard Forest since 2001

Two of the major results of our original soil warming study were that: (1) warming stimulated the decay of a labile soil carbon pool; and (2) it also increased the availability of inorganic nitrogen to plants. Because of the small size of the original warming plots an important question we have not been able to answer conclusively is: Has the increase in available nitrogen led to an increase in carbon storage in the vegetation? And if yes, how much? In a systems context an additional question is: What is the balance between the carbon lost from the soil and the carbon stored in the vegetation in response to soil warming? We are now addressing these important questions with a new warming experiment in the Barre Woods area of the Harvard Forest. The Barre Woods site was chosen because it is of similarities to the Prospect Hill site - stand age, tree species composition, and soil type. There is no evidence of a plow horizon at the Barre Woods site, though surrounding stone walls indicate past use as pastureland. Historical records indicate the site was destroyed during the 1938 hurricane and then regrew naturally. During the summer and fall of 2001 we buried 3.4 miles of heating cable in a 30 x 30m plot. Cables were buried at a 10cm depth, spaced 20cm apart. A second 30 x 30m area was delineated to serve as the control plot. Results from the original soil warming experiment confirmed that the soil disturbance associated with the installation of heating cables has had no effect on soil temperatures and only minor and variable impacts on soil moisture. In April 2002, we began a one-year period of baseline measurements before turning on the heat in the new megaplot. These measurements included nitrogen mineralization, trace gas fluxes (CO2, CH4, N2O), tree growth (dendrometer bands), an under story species survey, canopy foliage analysis (C:N, NIR), and lysimetry. Thermistors were installed in both plots to begin tracking soil temperatures. The baseline measurements have confirmed that there are no significant differences between the two plots for key ecosystem processes prior to the initiation of the warming manipulation. We will turn on the power in April 2003 to begin the "manipulation phase" of this study. From this study, we expect to determine whether or not warming results in the movement of nitrogen from the soil to the trees and to learn how this movement affects the net carbon balance of the ecosystem.