OSLO, Feb 27 (Reuters) - Deforestation in a single Indonesian province is releasing more greenhouse gases than the Netherlands, and the loss of habitats is threatening rare tigers and elephants, the WWF conservation group said on Wednesday.

It said that Riau province, covering one fifth of Indonesia's Sumatra island, had lost 65 percent of its forests in the past 25 years as companies used the land for pulpwood and palm oil plantations. Big peat swamps had also been cleared.

The changes meant Riau was "generating more annual greenhouse gas emissions than the Netherlands," according to the report by WWF and partners RSS GmbH -- a German forest monitoring group -- and Japan's Hokkaido University.

At the same time, the number of Sumatran elephants and tigers in the province plunged as the forests vanished, it said.

Trees store carbon dioxide, the main greenhouse gas, as they grow and emit it when they burn or rot. Peat swamps are also big natural stores of carbon. Worldwide, deforestation accounts for about 20 percent of greenhouse gas emissions.

The report said Riau accounted for average annual carbon emissions equivalent to 58 percent of Australia's yearly emissions, 39 percent of British emissions or 122 percent of the Netherlands' emissions.

The main companies operating in Riau were Singapore-based Asia Pulp & Paper and Asia Pacific Resources International Holdings Ltd (APRIL), it said.

Both have previously denied using timber from illegal sources. Staples Inc, the largest U.S. office supplies retailer, said on Feb. 8 that it stopped doing business with Asia Pulp & Paper because of environmental concerns.

The WWF said the Indonesian government promised at a 190-nation U.N. climate conference on the Indonesian island of Bali in December to provide incentives to protect remaining forests.

In the past 25 years, elephant populations in Riau fell 84 percent to only 210 animals, while tiger populations were estimated to have tumbled by 70 percent to perhaps just 192 individuals, the report said.

"Sumatra's elephants and tigers are disappearing even faster than their forests," said WWF International's Species Programme Director, Susan Lieberman. Driven from forests, they came more often into conflict with people and were killed.

-- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Tim Pearce)

AlertNet news is provided by