The forests of the Congo Basin constitute the second largest area of dense tropical rainforest in the world. Spread across about 200 millions hectares, from the Gulf of Guinea to the Albertine rift in Uganda, these forests harbor a unique biodiversity of worldwide importance. Nouabalé-Ndoki National Park is at the heart of this exceptional landscape.

About 80% of the forests of Central Africa are located between 300 and 1000m of altitude, forming lowland forests. Nouabalé-Ndoki National Park is part of an ecoregion called Northwester Congolian lowland forests, spreading from South-East Cameroon to Gabon and the northern half of the Republic of Congo. The Park is mainly made up of plateaus crossed by dently sloping valleys between 300 and 500m altitude.

The climate is equatorial, the temperature oscillates around 25°C with an amplitude of 2°C throughout the year. The seasonal distribution of rainfall is bimodal with an annual average of about 1,645mm, with a dry season between January and February that remains above 50mm/month.
The vegetation of the Park consists of a warm tropical rainforest characterized by a closed canopy. These conditions favor the formation of a mat of moist leaves on the ground and the spread of epiphytes (plants or fungi that grow on the surface of other plants). Where the canopy is most closed, the forest floor is almost devoid of sunlight. In the Park, this is the case in patches of forest dominated by a tree called Gilbertiodendron dewevrei. These forests are called monodominant, as opposed to tropical mixed forests where different species create a denser forest with thickets and low visibility.

Mixed terra firma forest is the most widespread and diverse vegetation type: this forest is highly heterogenous in its structure as well as in the number of plant species; trees can reach up to 50 m and the understory varies from extremely dense to open, with often an important presence of lianas. Extended patches of herbs belonging to the families of Marantaceae and Zingiberaceae can be found.

Swamps and seasonally flooded forests are also present. Another unique feature of the Park are “baïs”, or “yangas”. These are natural forest clearings occurring in humid areas., and the Park contains over 130 of such sites. A baï is usually crossed by flowing water, whereas a yanga occurs where water stagnates. These sites are dominated by Cyperaceae (sedges) and Graminae (grasses), and attract large mammals that feed on this vegetation.

The origin of these clearings is unclear, but they are likely maintained by animals visiting them to feed. This makes these sites targeted by poachers. It has been observed that at sites with high hunting pressure, the reduced use of bais by large mammals such elephants and buffaloes can lead to colonization of the open space by trees and shrubs.