Document: TOB-3-59-93

Forest ecosystem carbon and nitrogen storage after agricultural abandonment.

HOOKER, T.D.* ¹ and J.E.COMPTON ²

University of Rhode Island, Kingston, RI 02881, U.S.A. ¹
U.S. Environmental Protection Agency, Western Ecology Division, Corvallis, OR 97333, U.S.A. ²

Abstract:
Forests of the northeastern US are expected to serve as a substantial sink for atmospheric carbon and nitrogen, yet questions remain about the rate and distribution of sequestered C and N within these ecosystems after agricultural abandonment. To examine the change in ecosystem C and N pools during the first 114 years of ecosystem recovery in southern New England, we developed a chronosequence of ten previously cultivated sites with similar soils, land-use history and overstory vegetation (Pinus strobus). Total ecosystem C, including plant biomass, forest floor and soil to 70 cm, was significantly related to site age (r² = 0.92), while ecosystem N content did not change over time. Ecosystem C increased at an average rate of 2.05 Mg C ha^-1 yr^-1. Most of the sequestered C went into the plant biomass (73 %) and forest floor (17 %); the 20-70 cm soil depth (6 %) also increased significantly over the chronosequence. There was no significant change in ecosystem N content across the chronosequence (3.32 kg N ha^-1 yr^-1, P = 0.39); rather, N was re-allocated within the system. Nitrogen strongly decreased within the former plow layer (0-20 cm depth; -13.99 kg N ha^-1 yr^-1), and was offset by increases in the plant biomass (4.13 kg N ha^-1 yr^-1) and forest floor (11.62 kg N ha^-1 yr^-1). Organic matter C:N ratios increased with time in plant and mineral soil pools, resulting in an increase C:N from 15 to approximately 50 in all measured ecosystem pools. The lack of a significant increase in ecosystem N over 100 years of succession suggests that recovering ecosystems may be functioning closer to steady state rather than as a substantial net sink for N. While the patterns of C accumulation are similar to other estimates from northeastern forests, we present the novel finding of substantial C storage below the former plow layer during forest development (0.13 Mg C ha^-1 yr^-1 in the 20-70 cm soil depths).

Keywords: Carbon storage, nitrogen retention, land-use history, forest recovery, New England, white pine

This abstract is being presented at: 2:15 PM in session:
Oral Session #52: Carbon Storage in Ecosystems.