Role of competition in vegetation change: evolutionarily stable strategy analysis as a means for predicting change in vegetation distributions

Abstract:

One of the clearest differences among major vegetation types is allocation to woody biomass. Whether and to what extent plants invest in this long-lived tissue has a major impact on carbon storage and can have important feedbacks to the rising CO₂ in the atmosphere. Wood is a multifaceted structure. It can allow plants to escape from ground fires, the pressure of herbivores, and perhaps most importantly competition with other plants for light. Understanding the result of this final pressure requires an incorporation of individual-based interactions among plants. This can be a particularly difficult because of both high computational demands and errors in implementation and understanding of such complex models. We have made progress on both difficulties for understanding allocation to woody biomass among trees in forests. Across gradients in resource availability within forests, we find a significant influence of individual-based competition on dominant plant allocation to woody biomass. In model predictions and observed differences among forests globally major tradeoffs occur in allocation to woody biomass versus allocation to fine roots. This is driven by shifting importance of individual-based competition for light versus shared resources belowground, in particular water and nitrogen. Moving beyond forests to biome boundaries, transitions between grassland, savanna, and forest we see again that competition can play an important role. In these zones of rapid change however, population dynamics is not as simple as a steady-state closed-canopy forest. Disturbance dynamics including response to fire and drought stress are also important pressures on dominant plant strategies. Here I show progress in incorporating disturbance dynamics with individual based competition to predict and understand dominant plant strategies including allocation to woody biomass. Results indicate that the influence of competition varies with disturbance regime. With stochastic disturbance regimes we find coexistence among strategies should be common and lead to diverse communities that are less vulnerable to the sudden changes in disturbance regime that may accompany climate change than communities with a history of a steady or predictable environment.