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Abstract
Tropical savannas are a globally extensive biome prone to rapid vegetation change
in response to changing environmental conditions. Via a meta-analysis, we quantified
savanna woody vegetation change spanning the last century. We found a global trend
of woody encroachment that was established prior the 1980s. However, there is critical
regional variation in the magnitude of encroachment. Woody cover is increasing most
rapidly in the remaining uncleared savannas of South America, most likely due to fire
suppression and land fragmentation. In contrast, Australia has experienced low rates
of encroachment. When accounting for land use, African savannas have a mean rate annual
woody cover increase two and a half times that of Australian savannas. In Africa,
encroachment occurs across multiple land uses and is accelerating over time. In Africa
and Australia, rising atmospheric CO2 , changing land management and rainfall are
likely causes. We argue that the functional traits of each woody flora, specifically
the N-fixing ability and architecture of woody plants, are critical to predicting
encroachment over the next century and that African savannas are at high risk of widespread
vegetation change.