The WWF report, "Ecosystems in the Greater Mekong," says that from 1973 through 2009, the five countries comprising the region -- Cambodia, Laos, Myanmar, Thailand and Vietnam -- chopped down almost one-third of their forests for timber and to clear land for agriculture.
During that period, Cambodia lost 22 percent of its 1973 forest cover, Laos and Myanmar lost 24 percent and Thailand and Vietnam lost 43 percent.
"Core forests" a 1.86 square mile-block of uninterrupted forest, have dropped from 70 to 20 percent of total forest area, the analysis says.
"The Greater Mekong is at a crossroads," Peter Cutter, Landscape Conservation manager with WWF-Greater Mekong said in a release. "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."
WWF based its findings on analysis of satellite data and some of the findings conflict with official figures from the five countries, Voice of America reports.
The United Nations' Food and Agriculture Organization also has reported that official country figures in the region showed a decline in deforestation rates from 2000-10.
But WWF says those figures could be misleading because some countries identify agriculture plantations for rubber trees, cassava and palm oil as forested areas.
"Many protected areas exist in name only," Cutter said. "Even relatively secure protected areas are under intense pressure from poaching and timber theft, while others have been reduced in size by government's eager to cash in on land concessions to mining companies or plantation owners."
The report considers two possible future scenarios for the region's ecosystems: an unsustainable growth model in which deforestation and degradation continues as in the past decade, while the other scenario assumes slashing the annual deforestation rate by 50 percent and a future based on "green economy growth."
Under the "green" scenario, core forest areas still existing in 2009 across the five countries would remain intact.
"The green economy approach is the choice for a viable future in the Greater Mekong," Cutter said.
The report cites the Xayaburi Dam development as a key threat to the health and productivity of the Mekong River and delta. Laos has started construction on the controversial $3.8 billion hydroelectric project. About 95 percent of the dam's 1,260-megawatt capacity is intended for export to Thailand.