Forest inventory and analysis (FIA) database

The FIA program of the USDA Forest Service conducts nation-wide field-measured tree point-sample surveys using a systematic five-year inventory [26]. Each FIA plot inventories trees in four 7.2 meter fixed-radius subplots. Privacy issues require the latitude and longitude of plots be perturbed up to 0.8 km, and that some plots on private lands have locations swapped [27]. The influence of perturbing and swapping should be negligible in this study since FIA plots were aggregated into 50 km by 50 km grids. The FIA database (FIADB, version 5.1) was downloaded for the 31 easternmost USA states from the FIA DataMart (https://apps.fs.usda.gov/fia/datamart/) for the five-years 2009 to 2013.