Forest is commonly regarded as merely an endpoint in the continuum of tree densities observed in tropical savanna landscapes.  This perspective leads to the conclusion that the processes that determine the distribution of tropical forest and savanna are identical to those that determine patterns of tree density in tropical savannas.

Results/Conclusions

The objective of this presentation is to demonstrate why this is not correct, at least for the savannas and forests of Brazil.  There is almost no overlap is tree species composition between tropical savanna and adjacent forest, with these two groups of species differing in response to the environment as well their effects on the environment.  Forest species have denser crowns and higher leaf area indices than savanna species, allowing for forest species to more effectively exclude grasses.  Forest trees also have thinner bark, making them more susceptible to topkill and therefore requiring more time to escape the fire trap.  Although there are many other important differences between these two groups of species, these two differences alone are sufficient to result in fundamentally different tree-grass dynamics.  One consequence is that savanna-forest dynamics are much more strongly governed by positive feedbacks, typically resulting in sharp transitions in tree density.  These differences have important implications for modeling the dynamics of tropical vegetation in response to climate, disturbance, and resource availability.