A fundamental goal of biogeography is to understand the factors that drive spatial and temporal variability in forest growth across large areas. The Interior West Forest Inventory and Analysis program collected tree-ring data from thousands of plots that can be used to investigate controls on growth variability. Understanding the factors that control growth are important for managing species that could exhibit range shifts in response to climate warming.
To test for possible controls on tree growth variability, individual tree-ring data from Forest Inventory and Analysis plots were paired with other plot-level data such as elevation, longitude and latitude. This analysis used almost 3,000 Douglas-fir, ponderosa pine, pinyon, and limber pine from Idaho, Montana, Wyoming, Utah, and Colorado, spanning 12 degrees of latitude, and 15 degrees of longitude.
Contrary to widely held beliefs, researchers found no relationship between growth variability and elevation or latitude for all the species examined. There was a positive relationship found between growth variability and longitude, with more variability from west to east. The longitude relationship was largely driven by the presence of ponderosa pine and Douglas-fir in the easternmost forests of the Interior West.