Grass trumps trees with fire

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Ecologists have long assumed that forests, savannas, and grasslands change gradually over space and time, with tree cover responding linearly to gradients in precipitation, aridity, fire disturbance, and grazing pressure. However, a growing body of evidence suggests that these biomes are self-reinforcing and that transitions between them can be nonlinear, governed by feedbacks at local and regional scales (13). Two reports in this issue, by Staver et al. on page 230 (4) and by Hirota et al. on page 232 (5), find evidence for these feedbacks and transitions at the global scale. These results suggest that global climate change will be substantially influenced by nonlinear behaviors and feedbacks between biophysical and human systems.

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© 2011 American Association for the Advancement of Science. Publisher’s version of record: http://dx.doi.org/10.1126/science.1213908

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