Constituted in 1997, it is named after hoolock gibbon, the only ape found in India. The sanctuary is a patch of forest lying in Jorhat district of Assam. The vegetation is evergreen and semi-evergreen type occurring in layers. The upper canopy is dominated by the Hollong tree while the Nahar dominates the middle canopy. The lower canopy consists of evergreen shrubs and herbs. The most common species in the lower canopy is Dolu bamboo, Bojal bamboo and Jengu.
The now fragmented forest, which is surrounded by tea gardens, used to connect to forests that ran through Nagaland. Historically the area was covered by bojal bamboo interspersed by evergreen trees. Artificial regeneration programme was launched in 1924 which created plantations alongwith forest giving way to rich biodiversity. The sanctuary officially extends to the Dissoi Valley Reserve Forest, Dissoi Reserve Forest, and Tiru Hill Reserve Forest, which are used as dispersal areas for Indian elephants.
The sanctuary is well known for its non human primate diversity. Seven out of nine non human primate species found in North East India are found here like hoolock giboon, stump-tailed macaque, capped langur, rhesus macaque slow loris, Assamese macaque. Other animals include leopard, leopard cat, jungle cat, Chinese pangolin, wild boar, Asian elephant, Indian fox, civet cat, fox. The park is also a home to over 200 species of birds.
When to go
Best time to visit the sanctuary is February, March, June, July.
Demarcated as reserved forests in 1881, these used to once extend to Patkai mountain range.