Crown-condition classification: a guide to data collection and analysis
The Forest Inventory and Analysis (FIA) Program of the Forest Service, U.S. Department of Agriculture, conducts a national inventory of forests across the United States. A systematic subset of permanent inventory plots in 38 States is currently sampled every year for numerous forest health indicators. One of these indicators, crown-condition classification, is designed to estimate tree crown dimensions and assess the impact of crown stressors. The indicator features eight tree-level field measurements in addition to variables traditionally measured in conjunction with FIA inventories: vigor class, uncompacted live crown ratio, crown light exposure, crown position, crown density, crown dieback, foliage transparency, and crown diameter. Indicators of crown health derived from the crown data are intended for analyses at the State, regional, and national levels, and contribute to the core tabular output in standard FIA reports. Crown-condition measurements were originally implemented as part of the Forest Health Monitoring (FHM) Program in 1990. Except for crown diameter, these measurements were continued when the FIA Program assumed responsibility for FHM plot-based detection monitoring in 2000. This report describes in detail the data collection and analytical techniques recommended for crown-condition classification.