A 160-million-year-old forest
Khao Sok National Park protects a rainforest estimated to be 160 million years old, making it more ancient than the Amazon. Its immense age is due to a stable equatorial location. For millions of years, Thailand has remained near the equator, providing consistent warmth and rainfall. This stability allowed the forest to persist through multiple Pleistocene ice ages, which began around 2.58 million years ago. While glaciers covered high-latitude regions and droughts afflicted other parts of the tropics, Khao Sok's climate remained relatively unaffected, receiving enough rain to sustain the forest. This continuous existence turned the region into an important "glacial refugium"—a biological haven where species survived while they died out elsewhere.
The park itself was established on December 22, 1980, as Thailand's 22nd national park, covering 739 square kilometers. Its terrain is defined by dramatic limestone mountains, or "karsts," formed when tectonic shifts pushed up an ancient coral reef system. The tallest peak in the park reaches 960 meters. This rugged terrain has further protected the unique flora and fauna that found shelter here.
Genetic evidence of isolation
The story of this ancient refuge is written in the DNA of its inhabitants. Phylogeography—the study of the geographic distribution of genetic lineages—reveals how populations have moved and evolved over time. Studies in this region show a distinct genetic break between species on the Malay Peninsula and those in Indochina to the north, often corresponding to the narrowest part of the peninsula, the Isthmus of Kra.
During the ice ages, lower sea levels exposed the Sunda Shelf, creating a land bridge that connected mainland Southeast Asia with islands like Borneo and Sumatra. This allowed for the migration of species. As the ice melted and sea levels rose, populations became isolated. Genetic analysis of various species, from bulbuls (a type of bird) to binturongs, shows that populations in the peninsular region (including Khao Sok) diverged from their relatives in Indochina and the Greater Sundas during the Pliocene and Pleistocene epochs.
This long-term isolation in a stable environment promoted immense biodiversity. Khao Sok contains about 200 different floral species per hectare, compared to just 10 tree species per hectare in many European or North American forests. The constant, uninterrupted evolution has created a living laboratory, a reservoir of genetic diversity that provides a record of millions of years of natural history. The deep genetic divisions found in local species are direct evidence of the forest's role as a persistent sanctuary through periods of global climate change.