Summer rain in the southwestern US is delivered by the North American Monsoon (NAM), a climate system that is at least 10,000 years old. Given the semi-arid nature of this region and the importance of natural and human-dominated ecosystems to the resident population, we need to better understand how winter and summer precipitation is utilized by western forests in the face of climate variation. The central question of this project is to address if summer precipitation associated with the NAM complement and compensate for variation in winter precipitation in driving forest productivity and associated ecosystem processes.

We are using stable carbon and oxygen isotopes of tree rings in Ponderosa pine, collected across a latitudinal gradient from southern Arizona to Montana in order to examine how precipitation and vapor pressure deficit influence growth across the geographic range of this species.