The Global Extent and Determinants of Savanna and Forest as Alternative Biome States
Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states.
However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting
for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is
globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to
2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire
differentiates between savanna and forest. These may be alternative states over large areas, including
parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to
fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
Publication Date: 2011
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