Avoiding spurious conclusions from forest service estimates of timber volume, growth, removal, and mortality

Forest inventory statistics developed by the USDA Forest Service Forest Inventory and Analysis (FIA) units are useful in examining a variety of economic and biological issues, including forest-industry plant location, biological supplies of specific timber species, forest health, and long-term sustainability of timber resources. In general, these statistics accurately represent the resource, especially at the inventory-unit and state levels. However, several issues related to data collection must be understood to prevent spurious conclusions, especially when examining forest change characteristics such as removals, mortality, net growth, or the growth-removal ratio. Because FIA statistics are developed by sampling procedures, they are subject to sampling error. As the size of the forest area under study decreases, the number of observations used to develop FIA statistics decreases. The number of observations used to calculate FIA statistics can be particularly inadequate when examining net growth, removals, mortality, and growth-removal ratios of specific species for geographical areas smaller than inventory units.