The interactive effects of herbivory and rising temperatures on Quercus alba seedling demography: An experimental and observational test

There is little doubt that climate change alters interactions within communities. However, few experimental studies have provided insights on the effect of rising temperatures on White Oak (Quercus alba) seedling demography, a dominant tree species found in temperate deciduous forests in the eastern US. In this experiment, we investigate the potential for effects of insect herbivory and temperature on seedling survival. During the summer of 2010, we surveyed naturally occurring seedlings in an array of open-top chambers (OTCs) actively warmed year round from 0-5.5ºC above ambient in half degree increments. For the past two summers, we have recorded the intensity of insect herbivory, height, and number of leaves for each individual seedling (average seedlings plot^-1=85). In April 2011 we resurveyed these seedlings for survival. We used a multivariate logistic regression model that included temperature treatment, overall herbivory, height (cm), and number of leaves as predictors of survival. Both temperature (p=0.001) and herbivory (p=0.04) affected survival such that the risk of death was higher with rising temperatures and higher levels of herbivory. However, there was not an interaction between herbivory and temperature indicating that the effect of herbivory is not exacerbated by rising temperatures. Overall, the proportion of seedlings surviving after their first growing season was higher at ambient temperatures than at the warmest temperature treatments, and average herbivory was higher at ambient temperatures.  These results suggest a potential decline in this dominant tree species and a shift in the temperate deciduous tree community if temperatures continue to rise.