Humanizing savanna models: integrating natural factors and anthropogenic disturbance regimes to determine tree-grass dynamics in savannas

Explaining co-dominance of grasses and trees in savannas has confounded ecologists and biogeographers for decades. One reason is the complex nature of savanna human ecology; co-dominance can be caused by edaphic conditions, biotic factors, and/or human practices. New models consider savannas to be in disequilibrium and emphasize tree life histories, recognizing that events create opportunities for tree establishment. While much emphasis has been placed on how disturbances such as fire suppress trees, there has been less focus on how multiple disturbances interact to alter tree establishment. This study examines the impacts of hoe-farming, grazing, and burning on tree establishment and growth. It combines results from a 4-year field experiment with those from a long-term natural experiment. The study finds that the subtle changes in soil compaction and permeability as well as grass cover that result from hoe-farming counter the negative effects of fire on tree establishment and growth, especially on clay soils.