The Principle Investigator will determine the importance of the timing of water stress on changing the susceptibility of ponderosa pine Pinus ponderosa to an outbreak prone insect herbivore, Neodiprion gillettei . This research will test the hypothesis that environmental stress predisposes forests to insect outbreaks only when stress occurs at a time within the seasonal growth of the tree that creates a disequilibrium in the ecological balance between root and shoot growth. The specific hypothesis to be tested is that stress applied during the shoot growth phase will increase the root:shoot ratio and decrease susceptibility to insects; while stress applied during the root growth phase will decrease the root:shoot ratio and increase susceptibility to insects. The proposed research will test the widely held belief that stress predisposes forests to insect outbreaks. This research will also examine the fundamental process of seasonal allocation of carbon between roots and shoots and the response of herbivores to differences in this allocation pattern. These processes are strongly affected by variations in climate and likely are under genetic control. Better understanding of these processes will improve the predictability of the impact of insect herbivores on ponderosa pine forests under future unknown global climate conditions.
