Equatorial forest covers much of Republic of Congo's landscape, stretching from the Massif de Chaillu and Mayombe forests in the south to enormous tracts of primary forest in the north. These forests form part of the larger Congo Basin, a region that spans six countries and contains a quarter of the world's tropical forests. Congo's forests have not always covered their current area, but have naturally expanded and contracted over long periods of time and with ice ages and droughts.
Countrywide, more than 400 mammal species, 1 000 bird species, 700 fish and nearly 10 000 plant species, of which 3 000 are found nowhere else, have been recorded. The country's remote northern forests harbour the highest known gorilla densities, including an estimated 125 000 western lowland gorillas. A recent census by Wildlife Conservation Society also revealed that unexpectedly large numbers of great apes are alive and well in these remote northern forests. The news effectively doubled the estimated worldwide population of western lowland gorillas. Other large mammals include forest elephants, forest buffalo and the bongo.
The forests of the Congo have long been a source of food and shelter for hunter-gatherer societies, who have been hunting duikers, bush pigs, monkeys, and other mammals for generations. Animal products such as skins, horns, feathers, and bones play important roles in cultural and religious ceremonies. However, as human populations grow and their natural resource base continues to shrink due to industrial exploitation, they seek access into formerly remote areas. Increasingly, roads crisscross the forest, and urban societies are putting down new roots there. As a result, many of the region's large mammals, such as forest elephants, western gorillas, and chimpanzees, have become endangered.