Habitat and Ecology
Toro-Semliki is a mosaic of habitat and vegetation zones. Langdale-Brown et al. (1964) classified the reserve as “Combretum savanna,” but it is more appropriately described as a forest-grassland mosaic. Within the reserve, the Wasa and Mugiri rivers and their numerous tributaries support 30-50m tall gallery forests in 50-250m wide strips (Allan et al. 1996, Hunt unpublished data, Hunt and McGrew, 2002). The most common main canopy riverine tree species is Ugandan ironwood (Cynometra alexandri), followed by Millettia dura and Kigelia africana. The understory is dominated by Beilschmiedia ugandensis (SCP records), by far the most common tree in the riverine forests. Celtis africana, C. intergrifolia, C. mildbraedii, C. brownii, Albizia grandibracteata, A. coriaria, Chrysophyllum sp., Phoenix reclinata, Polyscias fulva, and Cola gigantea are also common (Allan et al. 1996; SCP records).
Tree stature declines as one moves away from the water sources, sometimes transitioning gradually to open-habitat species such as Acacia, Albizia and bushy species, but more often the transition from forest to grassland is abrupt. A few steps can take one from under the canopy of a 20 m tall Cola tree to fully open grassland. Some meters into the grassland Tamarindus indica trees are common, the fruits of which are consumed by nearly all primate species in the reserve.
Much of the rift floor is open grassland with Borassus palm, Acacia, Alibizia and Combretum dotting the landscape. Dominant grasses are Hyparrhenia, Imperata and Themeda spp. (Verner & Jenik 1984, Allan et al. 1996). Other important woody species include Balanites, Bauhinia, Capparis and Stereospermum (Verner & Jenik 1984, Allan et al. 1996, Hunt and McGrew, 2002).
The escarpment slope is predominantly grassland and open woodland, with Themeda and Chloris spp. grasses (Verner & Jenik 1984, Allan et al. 1996) and most of the same woody species common on the rift floor, Borassus, Acacia, Albizia and Bauhinia, but with the addition of Grewia and Ficus spp. The slopes are crosscut at approximately 1 km intervals by steep valleys with seasonal streams at the bottom; these streams support narrow bands of gallery or riverine forest. The gallery forests surrounding the Wasa and Mugiri differ little in their species mix. The Muguri River does not empty into the Wasa or Lake Albert, but terminates in the Jogo Jogo swamp (Figure 8), which is perennially water soaked; its vegetation is dominated by papyrus (Cyperus papyrus) and a profusion of Phoenix reclinata, among other species.
Near the shores of Lake Albert vegetation grades first into a dense, meter tall thicket-bushland and finally papyrus swamp (Cyperus papyrus).
Table 1: Toro-Semliki Tree Species (compiled from Verner & Jenik, 1978, Allan et al., 1993 and SCP records)
Acacia gerrardii
Acacia hockii
Acacia sieberiana
Alangium chinense
Albizia coriaria
Albizia ferruginea
Albizia grandibracteata
Albizia zygia
Allophyllus macrobotrys
Alstonia boonei
Anthocleista schweinfurthii
Apodytes dimidiata
Aurosala indica
Balanites aegyptiaca
Bauhinia (Piliostigma) thonningii
Beilschmiedia ugandensis
Bersama abyssinica
Borassus aethiopum
Bridelia sp.
Capparis tomentosa
Casoria labritata
Cassine buchanii
Celtis africana
Celtis intergrifolia
Celtis mildbraedii
Celtis wightii
Chionanthus africanus
Chrysophyllum pentagonocarpum
Chrysophyllum perpulchrum
Cnestis ugandensis
Cola gigantea
Combretum binderanum
Combretum ghasalense
Combretum molle
Cornus volkensii
Craibia brownii
Crateva adansonii
Croton macrostachyus
Cynometra alexandri
Dichrostachys glomerata
Diospyros abyssinica
Dombeya mukole
Dovyalis macrocalyx
Drypetes gerrardii
Erythrophleum suaveolens
Euclea racemosa schimperi
Euphorbia dawei
Fagara rubescens
Ficus mucuso
Ficus ottoniifolia
Ficus ovata
Ficus vallis-choudae
Flueggea virosa (Securinega virosa)
Funtumia africana
Gardenia erubescens
Grewia mollis
Gymnosporia senegalensis
Holoptelea grandis
Irvingia gabonensis
Kigelia africana
Lannea welwitschii
Leptaulus daphnoides
Lychnodiscus cerospermus 
Macaranga schweinfurthii
Maerua cafra
Markhamia lutea
Maytenus acuminata
Millettia dura
Oncoba spinosa
Phoenix reclinata
Phyllanthus sp. aff. P. inflatus
Polyscias fulva
Pseudospondias microcarpa
Psychotria sp.
Ptyregota mildbraedii
Pycnanthus angolensis
Ricinodendron heudelotii
Schrebera arborea
Securinega virosa
Spathodea campanulata
Stereospermum kunthianum
Strychnos mitis
Synsepalum brevipes
Tamarindus indica
Terminialia sp.
Trema orientalis
Trichilia prieuriana
Trichilia prieuriana
Vernonia amygdalina
Warburgia ugandensis
