Comprising five almost contiguous protected areas and spanning 230 km between Ta Phraya National Park on the Cambodian border in the east and Khao Yai National Park to the west, the boundaries of Dong Phayayen-Khao Yai Forest Complex follow contour lines that were originally drawn around remaining areas of forest and natural habitats, resulting in a well defined but complicated boundary. The overall size of the property adequately ensures complete representations of habitats and ecological processes, and with-well defined topographic, climatic and vegetal east-west gradients, it contains all major habitat types of eastern Thailand. Maintaining and re-establishing connectivity between the different ecological components of the complex remains a concern and a priority for the managing agency due to its direct impact on the integrity and value of the property.
More than 80% of Khao Yai National Park remains covered in evergreen or semi-evergreen forest, with much of it tall, good quality primary forest. There are significant areas of primary forest in each of the component protected areas of the complex, with moist and dry evergreen forests occurring in all the Protected Areas of the complex. Overall, the property represents a complex mosaic of all vegetation and habitat types remaining in northeast Thailand, including rainforest habitats, reflecting not only successional processes but also landform and soil diversity. As the last major area of extensive forests in northeastern Thailand, surrounded by almost completely converted landscapes, human pressures are significant and diverse including roads, incursions, tourism, and poaching. In some areas along the boundary, significant incursion and agricultural conversion have occurred and the lack of a clear external buffer zone results in competing land uses, bordering directly onto the property boundary.