Bwindi lies on the edge of the Albertine Rift, a valley which stretches from the northern tip of Lake Albert to the southern tip of Lake Tanganyika. This region is the most species rich region of comparable size in Africa for vertebrates and contains many endemic and threatened species. It is therefore a high priority area for conservation.
Bwindi is one of the few forests in East Africa where lowland and montane vegetation communities meet. It is believed to have served as a Pleistocene refugium, maintaining forest during the last ice age when most of the rest of the continent lacked forest cover and thus acted as a reservoir for forest dependent species that were lost elsewhere.
Bwindi is also a major catchment area, serving surrounding agricultural lands and the source of many rivers. These include the Ivi, Munyaga, Ishasha and Ntengyere, which drain into Lake Edward. The Ndego, Kanyamwabo and Shongi Rivers flow southwards towards Lake Mutanda.
A wide variety of vegetation occurs in the forest, broadly classified as medium altitude, moist evergreen and high altitude forest. The high altitude “Afromontane” forest is a highly restricted vegetation type on the African continent. The forest gets the name 'impenetrable' from the dense growth of herbs, vines and shrubs.
Bwindi’s forests have been given various names: Undifferentiated Moist Montane Forest (Langdale-Brown, 1960), Moist Montane Forest (Leggat and Osmaston, 1961), Tropical Low Montane Evergreen Rain Forest (Leggat and Osmaston, 1961), Parinari Forest (below 1500 m) and Prunus africana Moist Montane Forest (above 1500m), Langdale-Brown et al. (1964), Mixed Forest with Chrysophyllum (Lind and Morisson, 1974) and Moist Lower Montane Forest (Hamilton, 1982).
Approximately 40% of the park is occupied by mixed forest that occurs at all altitudes and is characterised by a canopy with various species that often include the Red stinkwood (Prunus Africana), Newtonia(Newtonia buchananii ), Symphonia globulifera, East African yellow wood (Podocarpus species), and Strombosia scheffleri. The understorey commonly includes Xymalos monospora, Neoboutonia macrocalyx, Myrianthus holstii, Teclea nobilis and Allophylus abyssinicus.
Some formations are more limited by altitude. At around 1500 meters above sea level, Parinari excelsa dominated forest covers approximately 10% of the total area. A further 11% is dominated by Newtonia buchananii at around 2000 meters, and 8% by Chrysophyllum gorungosanum at around 2200 meters. Bamboo (Arundinaria alpina) dominated vegetation occupies only about 1% of the forest at the highest altitude (2400 meters to 2560meters above sea level) and the remaining 30% supports various vegetation communities including swamps, herbaceous cover and colonising forest.
The lowest altitude vegetation occurs in the northern block. This area includes stands of Parinari along the Ishasha and Ihihizo river valleys. In the valleys where deeper soils occur, the forests still include Entandrophragma (African mahogany) often associated with Newtonia buchananii, Aningeria adolfi-friederici and Symphonia globulifera. In poorly drained areas, stands of Syzygium guineense occur. Ocotea usambarensis reaches large sizes. On the higher ridges Podocarpus occurs. Disturbed forests of Albizia species, Milletia dura and Canthium vulgare occur especially close to perimeter of the forest. With time such forest is replaced by a late secondary formation typified by species such as Ficalhoa laurifolia, Hagenia abyssinica, Maesopsis eminii, Polyscias fulva and Nuxia congesta and often includes large lianas.
The main forest block to the south includes Chrysophyllum spp. associated with Entandrophragma, Newtonia and Prunus africana but with smaller areas of dominant Parinari in some river valley bottoms. Podocarpus milanjianus, once common, has been greatly depleted by historical exploitation. Podocarpus gracilior remains common along swamp edges. The vegetation gets shorter at higher altitudes and often includes open herbaceous areas. These support thick growth of herbaceous plants including Mimulopsis solmsii, Mimulopsis arborescens and bracken fern (Pteridium aquillinum) and are a major feeding location for mountain gorillas, elephants and other ground dwelling animals. It is not clear how much of the open vegetation is natural and how much can be attributed to past anthropogenic disturbance including logging and fire during the early and mid 20th century. Elephant activity also contributes to the creation and maintenance of the open areas.
The swamps too are important for animals, hosting a number of restricted species of birds and amphibians. They appear to attract elephants (Loxodonta africana) during the dry season.
