Demand for farmland may strip the Greater Mekong region of a third of its remaining forest cover over the next two decades without swift government action, a leading conservation group warned Thursday.

Forests are being cleared for commodities such as rubber and rice while illegal logging is decimating many protected zones, WWF said in a report, adding a contentious dam on Mekong river will deepen already severe ecosystem damage.

"The Greater Mekong is at a crossroads," said Peter Cutter of the WFF, adding Cambodia, Laos and Myanmar lost between 22-24 percent of their forests from 1973 -- the first point of available data -- to 2009, while 43 percent of woodland was stripped from Thailand and Vietnam.

"One path leads to further declines in biodiversity and livelihoods... but if natural resources are managed responsibly, this region can pursue a course that will secure a healthy and prosperous future for its people."

Myanmar, a nation expected to undergo rapid economic growth after the end of junta rule, is on a "deforestation front" -- especially in its border areas -- as are the southern Mekong sections of Vietnam and Cambodia, the study found.

The reform-minded government has banned the export of logs from next year in a bid to tackle rampant illegal logging of its precious woods.

The WWF said large undisrupted areas of "core forest" across the region have also been fragmented by plantations and rapid urbanisation, while swathes of mangroves have been converted into rice paddy and for shrimp farms.

If deforestation continues, the report warned that 34 percent of remaining woodlands "will be lost and increasingly fragmented" by 2030 with only 14 percent of core forest left, destroying the habitat of wildlife including tigers and elephants.

Laos' Xayaburi dam was also highlighted as a "key threat" to the Mekong river ecosytem, saying it will have "devastating consequences" for 60 million people -- blocking fish and vital sediment from reaching the lower areas of the water system.

The $3.8 billion hydroelectric project, which is due to be completed in around five years, has sharply divided the four Mekong nations -- Laos, Vietnam, Cambodia and Thailand.

Impoverished Laos hopes the dam will help it become "the battery of Southeast Asia" and plans to sell most of the electricity to Thailand, but Cambodia and Vietnam say it could ruin their farming and fishing industries.

The report offers glimmers of hope saying Thailand has made great strides to protecting its forests -- the kingdom has an extensive network of national parks -- while the other nations have all backed policies to prevent deforestation.