Extreme climatic events challenge the capacity of vegetation models, including Dynamic Global Vegetation Models, to predict changes in plant species dynamics at local and regional spatial scales and over time periods relevant to ecologists and managers. Extreme climatic events are defined as large, infrequent, stochastic perturbations in weather patterns that change the outcome of entrained processes governing plant species abundances and composition. Directional, persistent changes in climate and the ongoing increase in atmospheric carbon dioxide concentration influence species interactions and vegetation dynamics indirectly by altering resource use patterns. Extreme climatic effects, like other pulsed disturbances, also directly affect species abundances.
The impact of extreme events on vegetation likely will be greatest when climatic extremes cause catastrophic, species-specific mortality, differentially affect species natality (rates of establishment), and initiate feedbacks that amplify initial changes in vegetation. Feedbacks may result from changes in disturbance regimes, plant-herbivore interactions, soil, and even long-term means of regional climate. In order to improve our ability to predict effects of climatic extremes on vegetation, we must better characterize likely effects on plant mortality and natality rates and incorporate feedbacks resulting from plant interactions with other organisms, soils, regional climate, and recurrent disturbance regimes.