Document Type

Conference Paper

Journal/Book Title/Conference

Pushing Boundaries: Forest Inventory and Analysis (FIA) Symposium




United States Department of Agriculture

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A fundamental goal of forest biogeography is to understand the factors that drive spatiotemporal variability in forest growth across large areas (e.g., states or regions). The ancillary collection of increment cores as part of the IW FIA Program represents an important non-traditional role for the development of unprecedented data sets. Individual-tree growth data from increment cores were paired with plot-level variables from the inventory to investigate the spatiotemporal growth patterns for Douglas-fir, ponderosa pine, common pinyon, and limber pine over the northern portion of the Interior West (Idaho, Montana, Wyoming, Utah, and Colorado). Based on dendrochronological theory proposed over 50 years ago, we tested three hypotheses that variability in ring-width increment (calculated as the Gini Coefficient): 1) would decrease as latitude increased; 2) would increase as continentality increases (i.e., west to east); and would decrease as elevation increased. The large range of observations (from 37° to 49° latitude, and from -117° to -104° longitude) were sufficient to test the first two hypotheses, but made it difficult to directly test hypothesis three (elevation). Generally, we did not confirm hypothesis one, except for common pinyon, which inhabits only a portion of the area examined. Hypothesis two was confirmed for the entire dataset, and the results were clearly driven by Douglas-fir and ponderosa pine. Hypothesis three was not supported for Douglas-fir or ponderosa pine, but was supported for common pinyon and limber pine. However, because the sample area encompasses such a huge range of latitude and longitude, which covary with elevation, we developed a corrected elevation. No significant relationships were found between ring-width variability and corrected elevation.