Livestock grazing poses one of the greatest dangers to giant pandas, having damaged more than one-third of the rare animals' habitat in a model nature reserve, a study by Chinese and US scientists has found.

A four-year investigation led by Li Binbin, assistant professor at Duke Kunshan University's Environmental Research Center, found that an increasing number of free-ranging livestock, mostly cattle and horses, inside the Wanglang National Nature Preserve has consumed most of the bamboo in some areas.

"Bamboo constitutes 99 percent of the giant pandas' diet," Li said. "The pandas have no choice but to move to higher areas of the mountains where bamboo can still be found."

"Long-term monitoring shows that pandas are being driven out of the areas heavily used by livestock, especially the park's valleys," Stuart Pimm, a professor of conservation biology at Duke University's Nicholas School of the Environment, was quoted as saying in a report released by Duke Kunshan University on Monday.

"These lower-elevation areas are crucial for giant pandas, especially during winter and spring," he said.

Li said overgrazing has reduced the regeneration of bamboo. Local farmers allow the livestock to roam the reserve at will and only go there twice a month to give the animals salt, she said.

"Over the past 15 years, while the number of livestock has increased by nine times, the panda habitat of the reserve has degraded by one-third," she said.

The Wanglang reserve, located in Sichuan province, is home to the largest population of wild giant pandas in China. The country has established 67 nature reserves to protect the animals.

Li and her team used 20 years of monitoring data to survey changes that have occurred in the geographical distribution of bamboo, pandas and livestock within the park. They modeled where degradation or loss of panda habitat has occurred and tracked livestock movement using GPS collars.

Li Sheng, assistant professor of conservation biology at Peking University, who worked with Li Binbin on the investigation, said that livestock grazing has become a problem at many reserves.

He said the interests of local communities, nature reserves and governments should all be considered to solve the current grazing problem.

"The same problem has been reported in many other reserves," Li Sheng said.

Li Binbin added: "The nature reserves have no enforcement power over the farmers who graze livestock. Those who have enforcement power, such as forestry bureaus, courts and forest public security departments, must work together to efficiently control overgrazing by livestock."

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