They believe several policy changes by the Chinese government may help the animals.

Without change, they say, the outlook for many panda populations would be dim.

Despite unprecedented work to conserve the species, habitat loss and development pressures continue to squeeze the pandas into smaller and less viable groups.

Writing in Science magazine, the authors say the panda should be a success story "as the world's most widely recognised conservation icon".

It enjoys a network of 33 nature reserves, and a captive breeding programme.

Human pressure

But habitat loss and fragmentation continue to depress its prospects, and China today has only an estimated 1,100 wild pandas, surviving in only a small part of their historic range.

The authors, from WWF and Beijing University, say human land use has restricted the pandas to about 24 populations at the edge of the Tibetan plateau.

In the Wolong nature reserve, they say, the three sub-populations of 30 to 45 pandas each have more than a tenfold chance of extinction by 2100 if they remain isolated from each other.

Most of China's panda populations have fewer than 50 animals, and are therefore in the authors' view too small to be viable in the long term.

More than half the pandas' habitat is protected, but the authors say the more urgent issue is to conserve habitat outside the existing reserve system, and to link fragmented patches.

Then, they say, panda numbers will rebound and grow.

One policy change they welcome is China's Natural Forest Conservation Programme (NFCP), which aims to increase forest cover in river basins to prevent any repetition of the disastrous 1998 floods.

To be implemented over 11 years, this will provide strict protection to all the remaining forests throughout the panda's range.

Seedlings distributed

The other initiative on which they pin their hopes is the Grain-to-Green policy, which aims to restore hillside agricultural land to forest or grassland over the next five to eight years.

Local communities will receive grain subsidies and seedlings for planting out.

Farmers will also receive a cash subsidy proportional to the amount of land they convert.

The authors write: "The NFCP and the Grain-to-Green policy provide a historic opportunity to move panda conservation from individual reserves to habitat conservation across landscapes."

But they sound a warning that the goals of development are sometimes incompatible with conservation.

They say integrating western China's development programme, which will lead to more infrastructure, hydropower, eco-tourism and investment, with conservation needs will be challenging.