Modeling tree mortality in response to short- and long-term environmental stresses

An understanding of how environmental stresses contribute to tree mortality is essential for predicting the impact of these stresses on forests. Utilizing a qualitative, mechanistic model of tree resource acquisition and allocation, I evaluated a conceptual model of the process of tree mortality. The conceptual mortality process model posits that tree mortality may result from short-term environmental stresses (e.g. drought or insect defoliation) acting on trees that have been predisposed to injury by long-term environmental stresses (e.g. air pollution or competition). A previous field study identified oaks that died in a manner consistent with this conceptual model and the mechanistic model provides further support for the conceptual model. When subjected to simulated short- and long-term stresses, the mechanistic model predicts changes in tree vigor that are similar to the changes in vigor predicted by the conceptual mortality process model. The simulation results also suggest a mechanism by which short-term environmental stresses affect tree physiology prior to death.