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Spatial variability of tree growth in the Interior West

Date: August 01, 2016

Tree growth is thought to predictably vary in relation to edaphic factors such as elevation, latitude, and longitude. Forest Inventory and Analysis tree-ring data from Idaho, Montana, Wyoming, Utah, and Colorado were used to test this idea


Background

Four graphs displaying location and species of tree-ring data plots, growth and elevation at these locations.
(a) Location and species of tree-ring data collected on Forest Inventory and Analysis plots (n=2,949), (b) relationship between growth variability and latitude, (c) longitude, and (d) elevation.
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.

Key Findings

  • Geographically unbiased tree-ring data collected through the Forest Inventory and Analysis program represents a population-level approach to assessing growth variability.
  • Growth variability showed no patterns across latitude from 37 to 49 degrees or across elevation.
  • Growth variability increased across longitude from -117 to -105 degrees.


Principal Investigators: 
Principal Investigators - External: 
James N. Long - Utah State University
Simon Wang - Utah State University