In prehistoric times montane forest occupied one-third of the territory of present-day Rwanda. Naturally occurring vegetation is now mostly restricted to the three National Parks, with terraced agriculture dominating the rest of the country. Nyungwe, the largest remaining tract of forest, contains 200 species of tree as well as orchids and begonias. Vegetation in the Volcanoes National Park is mostly bamboo and moorland, with small areas of forest. By contrast, Akagera has a savanna ecosystem in which acacia dominates the flora. There are several rare or endangered plant species in Akagera, including Markhamia lutea and Eulophia guineensis.
The greatest diversity of large mammals is found in the three National Parks, which are designated conservation areas. Akagera contains typical savanna animals such as giraffes and elephants, while Volcanoes is home to an estimated one-third of the worldwide mountain gorilla population. Nyungwe Forest boasts thirteen primate species including chimpanzees and Ruwenzori colobus arboreal monkeys; the Ruwenzori colobus move in groups of up to 400 individuals, the largest troop size of any primate in Africa.
There are 670 bird species in Rwanda, with variation between the east and the west. Nyungwe Forest, in the west, has 280 recorded species, of which 26 are endemic to the Albertine Rift; endemic species include the Ruwenzori Turaco and Handsome Francolin. Eastern Rwanda, by contrast, features savanna birds such as the Black-headed Gonolek and those associated with swamps and lakes, including storks and cranes.