Using forest inventory and analysis plots to estimate sample sizes for alternative inventory methods

Abstract

USDA Forest Service Forest Inventory and Analysis (FIA) fixed-radius sampling protocols can be modified to sample using other protocols such as variable-radius. When an agency lacks data from their forests, altered FIA data can be used to sample across a wide range of site conditions at a variety of scales. The FIA database contains horizontal distances from plot center to every sampled tree. Sample trees can be selected with variable-radius methods by using these distances along with particular basal area factor (BAF) critical distances. An example is provided in which sample sizes for 10 (2.296 BAF metric) and 20 (4.592 BAF metric) BAFs are calculated by cover type for lands owned by a large public land agency. This agency wants to determine statistically valid sample sizes for 10 (2.296 BAF metric) and 20 (4.592 BAF metric) BAFs but lacks individual sample point data and hence cannot estimate the inherent variability in their stands. FIA data can also be modified to sample using other methods such as nth tree sampling.