What does nonforest land contribute to the global C balance?
Jennifer Jenkins, USDA Forest Service
Urbanized land (i.e. "developed" land) covers 98.3 million acres in the United States, and the acreage in this category increased by 25% between 1982 and 1997, based on statistics from the 1997 USDA Natural Resource Inventory. Despite this large and growing land base, studies using land-based approaches to quantify land-atmosphere C exchange in the US have overlooked urbanized areas as potential contributors to national and global C cycles. From an inventory of vegetation on "nonforest" (predominantly urbanized) land in and around Baltimore, MD conducted in 1999 by the USDA Forest Service Forest Inventory and Analysis (FIA) program, annual wood production and tree biomass values on nonforest land were approximately 22% and 25%, respectively, of corresponding values on land classified as forest. We estimate that vegetation on nonforest land in Maryland currently stores 25.9 x 106 Mg C. Annual gross C sequestration in vegetation on nonforest land in Maryland is approximately 0.6 x 106 Mg C yr-1.
Extrapolating this result to the northeastern US, we estimate that vegetation on developed land in the northeastern US currently stores 280.2 x 106 Mg C. Vegetation on developed land in the northeastern US sequesters 14.5 x 106 Mg C annually. We suggest that vegetation on developed land in the entire United States could store an additional 0.03 to 0.04 Pg C yr-1 in the US, which would be as much as 10% of the existing "missing" North American terrestrial sink of 0.35 to 0.90 Pg C yr-1.