The Legacy of Subsistence Agriculture on New England 's Successional Forest Soils:
A 25-year Direct Measurement Perspective

Christopher Fuller

Brown University, ScB, December 2006.

The early study of forest ecosystems was largely driven by a global increase in deforestation. Science was trying to determine the long term effects of clear-cutting and other forest harvesting techniques on the remaining components. Everyone could see that the forest did re-grow, but questioned whether the system had been permanently damaged by the action. This early study focused on the easily accessible and largely visible components of the system, slash, forest floor and the uppermost mineral soil. Although the results were largely based on a chronosequence technique that traded space for time, and surface data, they did suggest that recovery was generally possible after approximately a century. In 1980 a study of New Hampshire forests suggested an extension of this recovery period to two centuries for agriculturally modified soils, clear-cut and burned in place forests with later annual plowing. Recently the majority of the research has moved beyond this simple presumption of recovery to the more detailed work of soil nutrients and carbon flux in the increasingly relevant topics of agricultural production and global climate change. Northern temperate forest systems have been identified as potential atmospheric carbon dioxide sinks.

This paper challenges the predictions of a 200-year soil carbon recovery period reported in the earlier mentioned 1980 old-field chronosequence that was re-sampled in 1992 and 2005 as well as the paradigm that soil carbon recovery is possible. This unprecedented 25-year direct measurement of effect of colonial agriculture on the development of re-growing forests suggests that the soils of 19th century farms of central New Hampshire are in actuality, a source of carbon dioxide to the atmosphere. I also found evidence that the plowed layer is predisposed to increased soil respiration and that the assumed steady state references, vital to the chronosequence technique, are actually in decline. I show that these results correlate with increases in median annual temperature, and increased incidence of soil frost reported in the area. These results suggest that climate change may be retarding the ability of the soil to retain carbon stocks and questions the ability of these re-growing forests to aid in the mitigation of atmospheric carbon dioxide.