Model Assesses the Influence of Drought Stress on Forest Relative to Other Factors
Climate change is expected to affect forest landscape dynamics in many ways, but one of the most important direct effects will probably be drought stress. Forest Service scientists used weather and Forest Inventory Analysis (FIA) data to develop equations to predict drought mortality and incorporated them into a landscape forest dynamics model (LANDIS-II). They found that incorporating drought as a tree-killing disturbance does indeed significantly modify forest composition and landscape dynamics.
Forest Service scientists combined data from weather stations and forest inventory plots across the upper Midwest to generate predictive equations using measures of drought stress to predict tree biomass lost to mortality for tree species with varying drought sensitivity. These predictive equations were used to develop a drought extension for the LANDIS-II model, which was applied to a test landscape in Wisconsin to assess the influence of drought on forest dynamics relative to other factors such as stand-replacing disturbance and site characteristics (e.g., soil).
The simulations showed that drought stress does significantly affect species composition and total biomass. Scientists were able to conclude that, for the upper Midwest, (1) a drought-induced tree mortality signal can be detected using FIA data; (2) tree species respond primarily to the length of drought events rather than their severity; (3) the differences in drought tolerance of tree species can be quantified; and (4) future increases in drought could very well bring changes to forest composition.