FIA tree species code changes through time

<p>This repository contains data and R code that evaluates changes in species code (SPCD) within USDA Forest Service Forest Inventory and Analysis (FIA) Program tree remeasurements. The FIA Program conducts the national forest inventory of the United States, with a spatially representative sample of over 140,000 forested plots across the conterminous U.S. (CONUS), Alaska, Hawaii, and the U.S. Territories and Affiliated Islands. In this project, we linked remeasurements of individual trees across CONUS FIA plots to determine how often tree species identification (SPCD) changed, how rates of SPCD changes varied across the country, and how decisions to rectify these differences can lead to differences in estimates of species range centroids, plot-level species richness, and both tree-level and population-level estimates of aboveground carbon. </p>

<p>The data file included in this repository contains a table in CSV format that includes >3 million unique trees that have been remeasured in FIA plots. The table includes columns of tree control number (CN) for the most recent measurement of live trees and their previous CNs through past measurements. These CNs can be used to link to additional tree-level data from the FIA database. This table also includes columns of tree SPCD at each remeasurement, columns flagging whether the SPCD changed between remeasurements, and what each tree's first and current recorded SPCDs were.</p>

<p>R code included in this repository shows how this data file was created. It includes instructions for downloading the SQLite FIA database from the FIA DataMart (https://apps.fs.usda.gov/fia/datamart/datamart.html), how to use the 'odbc' and 'RSQLite' packages to perform SQL queries on the database, and steps for constructing the trees-through-time data table using the 'dplyr' and 'data.table' packages. </p>