Title: Actual Evapotranspiration (AET) and tree species richness in the eastern U.S.A.
Author: Fan, Weihong; Waring, Richard H.;
Source: In: McWilliams, Will; Moisen, Gretchen; Czaplewski, Ray, comps. Forest Inventory and Analysis (FIA) Symposium 2008; October 21-23, 2008; Park City, UT. Proc. RMRS-P-56CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 13 p.
Publication Series: Proceedings (P)
Description: Although many studies confirm that competition and disturbance play important roles in determining tree diversity locally, climatic constraints become increasingly important at broader geographic scales. We evaluate the extent that annual actual evapotranspiration (AET) might account for observed variation in tree diversity across the entire eastern U.S. and within 24 Level III ecoregions designated by the Environmental Protection Agency. To estimate tree diversity, we extracted data from a total of 87,137 Forest Inventory and Analysis (FIA) survey plots. For each 1000 km2 cell with ≥15 plots, logarithmic functions were derived to predict the number of species encountered per hectare (equivalent to 17 fixed-radius plots). Across the region, tree diversity exhibited a humped-shaped pattern with AET (r2=0.49, P < 0.0001). Stratifying ecoregions by AET, which increases from north to south, winter temperature emerged as a significant variable where AET averaged <800 mm.yr-1, whereas summer temperature accounted for much of the variation where AET was between 800 to 950 mm.yr-1. In ecoregions with AET>1100 mm.yr-1, significant variation in tree diversity was associated with seasonal differences in precipitation. We conclude that across the eastern U.S., AET provides a reasonable prediction of regional variation in tree diversity, especially where AET is < 800 mm.yr-1.
Keywords: AET, AET stratification, tree species richness, tree diversity, level III ecoregions, FIA database, environmental variables of species diversity, the eastern US
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Fan, Weihong; Waring, Richard H. 2009. Actual Evapotranspiration (AET) and tree species richness in the eastern U.S.A. In: McWilliams, Will; Moisen, Gretchen; Czaplewski, Ray, comps. Forest Inventory and Analysis (FIA) Symposium 2008; October 21-23, 2008; Park City, UT. Proc. RMRS-P-56CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 13 p.
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