Spatial Patterns of Aboveground Production and Mortality of Woody Biomass for Eastern U.S. Forests

We developed maps of aboveground production and mortality of woody biomass for forests of the eastern United States based on data collected from an extensive network of permanent plots remeasured by the U.S. Forest Service Forest Inventory and Analysis units (FIA). Forest volume inventory data for growth and mortality were converted to units of aboveground biomass at the county level for hardwood and softwood forest types. Aboveground production of woody biomass (APWB) for hardwood forests ranged from 0.6 to 28 Mg·ha−1·yr−1 and averaged 5.2 Mg·ha−1·yr−1. For softwood forests, APWB ranged from 0.2 to 31 Mg·ha−1·yr−1 and averaged 4.9 Mg·ha−1·yr−1. Aboveground production of woody biomass was generally highest in southeastern and southern counties, mostly along an arc from southern Virginia to Louisiana and eastern Texas. Although this pattern is generally the result we would expect from the general climatic gradients of the region, it was confounded by the effects of different forest management intensities. No clear spatial pattern of mortality of woody biomass (MWB) existed, except for a distinct area of high mortality in South Carolina due to Hurricane Hugo in 1989. For hardwood forests, MWB ranged from 0 to 15 Mg·ha−1·yr−1 and averaged 1.1 Mg·ha−1·yr−1. The average MWB for softwood forests was 0.6 Mg·ha−1·yr−1 with a range of 0–10 Mg·ha−1·yr−1. The rate of MWB on an aboveground biomass basis averaged <1%/yr for both hardwood and softwood forests. A first-order carbon budget (the sum of the net change in carbon storage in all live trees, dead wood, and long-lived wood products) shows that eastern U.S. forests accumulated ∼174 Tg C/yr during the late 1980s and early 1990s. Although the root and soil pools are not included in this budget, it is likely that the forests are accumulating carbon in these components too, because the eastern forests are for the most part in various stages of regrowth and recovery from past human land uses and active forest management.