Drought induced tree mortality and ensuing bark beetle outbreaks in southwestern pinyon-juniper woodlands

The current drought and ensuing bark beetle outbreaks during 2002 to 2004 in the Southwest have greatly increased tree mortality in pinyon-juniper wood- lands. We studied causes and consequences of the drought-induced mortality. First, we tested the paradigm that high stand densities in pinyon-juniper woodlands would increase tree mortality. Stand densities did not impact mortality levels for either tree species, which does not support tree thinning to reduce susceptibility to drought- bark beetle outbreaks. Second, we monitored changes in stand structure and dead woody biomass to test whether altered fuel loads might affect potential fire behavior. Mortality can significantly affect torching index but has little effect on crowning index. Finally, we predicted that ground-dwelling arthropods would be highly responsive to habitat changes resulting from dead trees. Although we found significant responses, they were not as strong as predicted. Together, these results suggest that impacts of drought-induced tree mortality may not appear for years or decades after a major mortality event.