Post-drought growth responses of Western juniper (Juniperus occidentalis var. occidentalis) in Central Oregon

Abstract

Increased atmospheric CO2 may affect the physiological response of natural trees to drought. We examined radial growth rates developed from five western juniper chronologies to determine if post-drought growth responses have changed. Using prior year October to current year June precipitation from 1896-1998, we identified drought recovery years as having standardized scores (z-scores) > 0 and preceded by a year with a z-score <0.05) for four of the five sites, and for all sites combined. These results are consistent with the drought-ameliorating effects of CO2 shown by controlled laboratory studies and suggest that rising levels of atmospheric CO2 may impact western juniper growth rates.