Giant pandas live in China's mountainous Sichuan, Shaanxi and Gansu provinces. (Binbin Li)

The pandas' shaggy ranks appear to be swelling deep in the Chinese wilderness. A national survey of the bamboo forests, completed in 2013, reported 1,864 giant pandas. The survey completed a decade before counted fewer than 1,600. Population numbers alone, though, paint an incomplete picture.

Using satellite data, a team of scientists mapped 40 years' worth of changes in panda habitat, the researchers reported in a new study published Monday in Nature Ecology & Evolution. Although there are more pandas, the area they live in is smaller than when the International Union for the Conservation of Nature, or IUCN, first listed pandas as endangered in 1988.

“This study is the first that provides a 40-year analysis of panda habitat changes across the entire panda range,” said Jianguo Liu, a Michigan State University environmental scientist and an author of the new work. “It shows that the panda habitat continued to decline until 2001, when the panda habitat began to recover.”

In September 2016, the IUCN upgraded the pandas from endangered, a status the species held for 28 years. The animals are now classified under the IUCN as vulnerable — not yet a healthy population, but a step back from extinction's edge.

“The adjustment is a recognition of panda conservation success so far. But pandas are still facing threats, especially climate change. It does not mean that panda conservation should stop,” Liu said.

Liu and his colleagues used satellite images from four years: 1976, 1988, 2001 and 2013. From 1976 to 2001, panda habitat decreased by 4.9 percent. From 2001 to 2013 it increased slightly, by 0.4 percent. Roads, rivers and tunnels bisect the forests. The average forest patch decreased in size by 24 percent from 1976 to 2001, and only grew by 1.8 percent from 2001 to 2013. The sections of panda habitat in isolation have continuously increased, from less than 400 in 1976 to nearly 550 by 2013.

“There have been some good changes and some bad changes,” said study author Stuart Pimm, a conservation ecologist at Duke University. China ceased logging operations in the panda habitats 20 years ago. The end of this deforestation, Pimm said, was a “huge positive step.”

But the infrastructure around the forests is expanding. Bumpy roads that a decade ago would require hours to navigate have been replaced with pavement. “The panda habitat has been diced and sliced into smaller and smaller pieces,” Pimm said. Pictured from the sky, new roads cross the mountain forests like fractured glass increasingly under pressure.

The worry, he said, is that pandas have been split into isolated populations. This is particularly troubling if there are clusters of all one sex. Unless the males and females can get together, after all, there are no baby pandas. The conservationists recommend that developers build tunnels, which the pandas can cross above, rather than roads over the mountains.

For 300-pound animals, giant pandas are tough to track. They're shy. They live high in wet, mountainous forests. Conservationists rarely see their subjects of study.

Population surveys, too, rely on indirect methods. The 2013 count, China's fourth national survey, required 60,000 person-days. Surveyors combed 17,000 square miles and collected bamboo scraps from panda dung. Each panda has unique tooth marks, akin to a fingerprint, which allows surveyors to tally the animals.

As intensive as the surveys have been, the methods and areas covered were not always consistent. “It's been hard to come up with assessments that are truly comparative,” Pimm said, over the past 40 years. The satellite study is one of the few remote sensing surveys to offer such a long retrospective view of panda habitat.

“Conserving pandas is the responsibility of not only China, but also all people around the world,” Liu said. “For example, CO2 emissions outside China will contribute to global climate change and have impacts on the panda future.”

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