Quantifying the abundance of co-occurring conifers along Inland Northwest (USA) climate gradients.
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 degree-days >5 degrees C 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 degree-days (degree-days < 0 degrees C). 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.
Rehfeldt
Gerald E
GE
Rocky Mountain Research Station, USDA Forest Service, Forestry Sciences Laboratory, Moscow, Idaho 83843, USA. jrehfeldt@gmail.com
Ferguson
Dennis E
DE
Crookston
Nicholas L
NL
D002980:Climate; D017753:Ecosystem; D015205:Northwestern United States; D064028:Tracheophyta / Q000502:physiology*; D014197:Trees