Genetic consequences of extreme drought on a foundation tree and its dependent community

Background/Question/Methods   Current climate models predict a shift to warmer, drier conditions in the southwestern US.While major shifts in plant distribution are expected to follow these climate changes, interactions among species and intraspecific genetic variation could alter these projections. In this presentation, we examine the drought-related mortality of pinyon pine (Pinus edulis) in northern Arizona focusing on trees that show genetically-based resistance or susceptibility to two non-lethal herbivores, a shoot-boring moth and a needle feeding scale. We highlight recent studies from both field and greenhouse experiments that demonstrate differential mortality between resistant and susceptible pinyons to both herbivores and also show that the two herbivores vary in their responses to drought stress. Finally, we utilize assessments of insect and ectomycorrhizal fungi (EMF) communities associated with resistant and susceptible trees to understand the extended consequences of genetically influenced drought mortality.

Results/Conclusions   Our recent studies demonstrate that interactions among pinyons, herbivores and drought stress are strongly dependent upon the genotype of the pinyon and which herbivore is involved. For example, pinyons that were resistant to the moth were 3x as likely to experience drought related mortality than susceptible individuals. In contrast however, juvenile pinyons resistant to the scale herbivore were more likely to survive the drought than scale susceptible trees. Interestingly, the response of the herbivores themselves also showed opposite patterns. The scale was much more abundant under drought conditions, while moth abundance actually decreased during the drought years. Our recent findings also show that associated insect and EMF communities differ between resistant and susceptible pinyons. Taken together, our findings suggest that genetic variation in a tree population can be an important factor in determining its response to future climate change, and argue for the inclusion of genetics into models developed to understand the consequences of climate change. We also argue that climate change driven changes in a foundation species will have important impacts on associated communities and possibly alter ecosystem processes that are important in recovery from extreme climatic events.