Enviva annually sources from more than 400 property owners in each facility’s “drain area.” Each drain area has an average radius of approximately 75 miles, which encompasses approximately 12 million acres (4.9 million hectares). Of these acres, approximately 7 million acres (6 in 10 acres) are standing timberland (this number will vary by location but is a measurable estimate). In order to accurately monitor growth/drain ratios, Enviva currently uses Forest Inventory Analysis (FIA) which is administered by the USDA Forest Service. FIA randomly places perpetual inventory timber plots throughout all forested regions in the United States. Each plot is visited and assessed every 5 years on a rotational basis. These plots are confidential, so that no one can influence the data. Every tree on each plot is measured (diameter and height) and accounted for.
Through these analyses, FIA can very quickly assess growth/drain ratios in specific areas as well as the general status of regional timberland. As an example, through FIA data, the U.S. Forest Service has been able to assess that U.S. forests are growing more timber than is being harvested every year. Since 1953, the volume of growing stocks on timberland in the south has increased from 148 billion cubic feet (4.2 billion cubic meters) to over 288 billion cubic feet (8.2 billion cubic meters). Since 1997, growing stocks in the south have increased by 32 billion cubic feet (1 billion cubic meters) or almost 13 percent (Source: U.S.D.A. Forest Service: U.S. Forest Resource Facts and Historical Trends 2010).