Print PageSavannas are characterized by the co-dominance of C4-grasses and trees and they cover large areas of the earth's land surface. Despite intense research during the last decades, there is still no consensus how grasses and tree manage to coexist in savannas while out-competing each other in grasslands and forests. It is further not clear which biotic and abiotic factors allowed savannas to evolve and to spread on a paleo-ecological time scale and how savannas respond to anticipated climate change. It has been proposed that interactions between low atmospheric CO2 concentrations and fire allowed C4-grasses to gain advantage over trees and to spread in the late Miocene. The spread of C4-grasses and fire promoted the establishment of fire resistant tree species that managed to coexist with grasses in savannas.
Results/Conclusions
We developed an adaptive dynamic savanna vegetation model to identify climate conditions that allow typical savanna plant communities to evolve. The model lets single plants have individual trait combinations and it uses genetic optimization algorithms to let plant communities adapt to the environmental conditions by adjusting the trait combinations. Many of the plant traits used in the model allow grasses and trees to develop strategies for coexistence and for survival in fire driven ecosystems. For instance, flexible root and canopy forms allow niche separation between grasses and trees, variable rates of carbon allocation to bark and storage compartments increase the regrowth capacity of vegetation after fire and hence fire resistance. Using the model we further explored how climate change influences plant communities in savannas and hence the savanna biome boundaries. This study contributes to our understanding of savanna ecosystems as it integrates plant physiology, population dynamics and community assembly as well as disturbance and competition based explanations of savanna dynamics within one modeling framework.
