Few wildland areas in the tropics contain as rich array of habitat types as the Leuser Ecosystem. More than 100 kms of the western boundary of the Leuser Ecosystem lie along the coasts of the Indian Ocean. Behind these sandy beaches lie fresh water peat swamps, while these in turn are backed Human population distribution and density in Aceh by lowland rainforests which eventually sweep upwards to more than 3000 meters where the forests give way to alpine meadows.

A large rift valley running northwest/southeast divides the Leuser Ecosystem in two. The range to the west is usually referred to as the Bukit Barisan. To the east lies the Bandahara mountain range. This also reaches heights close to 3000 meters and includes three volcanoes and a high altitude plateau. The Bandahara range ultimately plunges steeply down to the lowland forests to the east which reach almost to the mangrove swamps that border the Malacca straits. To the north and south of the Leuser Ecosystem lie two volcanic calderas testifying to the violent geologic history to the area. Both these calderas are filled with water forming the Lakes Lau Tawar in the north and Danau Toba (one of the largest calderas in the world) to the south.