An inventory of carbon storage in forest soil and down woody material of the United States

The U.S. Department of Agriculture Forest Service Forest Inventory and Analysis (FIA) program conducts an annual forest inventory which includes measurements of down and dead wood and soil characteristics as indicators of forest health. Both indicators are measured on a systematic nationwide array of approximately 7800 plots where each one may represent up to 38,850 ha. Between 10 and 20% of these plots are measured every year. The down woody material indicator includes measurements of coarse and fine downed and deadwood. Carbon (C) storage in these down woody materials is estimated using line intersect biomass estimators and C conversion constants. The soil quality indicator is based on a range of statistically based methods including volumetric sampling of the forest floor and the collection of mineral soil cores representing depth increments of 0-10 and 10-20 cm. Carbon content of the soil samples is determined by dry combustion. We combined indicator measurements collected over 3 years (2001-2003) to estimate the C storage in soil and down wood in forests of the United States. Preliminary results suggest that as much as 80 Mg ha^-1 of C may be stored in forest soil and down woody material in some locations. Carbon storage by component is roughly ranked as follows: 0-10 cm mineral soil >10-20 cm mineral soil > the forest floor > coarse wood > fine wood. Preliminary spatial analysis of the C stocks in the North Central region of the United States illustrates the influences of latitude on C storage