Rocky Mountain Research Station

Title: Quantifying the abundance of co-occurring conifers along Inland Northwest (USA) climate gradients

Author: Rehfeldt Gerald E.; Ferguson Dennis E.; Crookston Nicholas L.

Date: 2008

Source: Ecology. 89(8): 2127-2139.

Description: The occurrence and abundance of conifers along climate gradients in the Inland Northwest (USA) was assessed using data from 5082 field plots, 81% of which were forested. Analyses using the Random Forests classification tree revealed that the sequential distribution of species along an altitudinal gradient could be predicted with reasonable accuracy from a single climate variable, a growing-season dryness index, calculated from the ratio of degreedays .58C that accumulate in the frost-free season to the summer precipitation. While the appearance and departure of species in an ascending altitudinal sequence were closely related to the dryness index, the departure was most easily visualized in relation to negative degreedays (degree-days ,08C). The results were in close agreement with the works of descriptive ecologists. A Weibull response function was used to predict from climate variables the abundance and occurrence probabilities of each species, using binned data. The fit of the models was excellent, generally accounting for .90% of the variance among 100 classes.

Keywords: altitudinal distributions, climatic distributions, conifers, Inland Northwest, USA, Random Forests, realized climate niche, species abundance, Weibull regressions

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Citation

Rehfeldt Gerald E.; Ferguson Dennis E.; Crookston Nicholas L.  2008.  Quantifying the abundance of co-occurring conifers along Inland Northwest (USA) climate gradients.   Ecology. 89(8): 2127-2139..