Ecosystems can change at 'tipping point'

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WAGENINGEN, Netherlands, Oct. 13 (UPI) -- Tropical ecosystems have two basic varieties, forest or grassland, but can switch abruptly between the two with little middle ground, European scientists say.

Researchers say the "tipping point" phenomenon means many of the ecosystems are particularly vulnerable to future changes such as rising temperature or other climatic variations, NewScientist.com reported Thursday.

With only slight shifts in rainfall or other factors, for example, people living in a grassland might suddenly find themselves in a tropical rainforest populated by a different mix of plants and animals where livelihoods might have to change dramatically.

"That transition is not going to happen smoothly," Milena Holmgren, an ecologist at Wageningen University in the Netherlands, said. "The evidence is showing there are these big jumps."

If a grassy savanna starts receiving more rain it stays a savanna with the same percentage of tree cover for quite some time, researchers said, until at some crucial level of extra rainfall it suddenly switches to a full-fledged forest.

Most current global climate models assume a smooth transition between savanna and forest as temperatures and rainfall change, but the new research suggests forests could appear or disappear quickly, scientists said.