Broadleaved forests

Low- and medium-altitude evergreen rainforests on firm ground (Lebrun and Gilbert's "equatorial rainforests") account for about a third of the country's closed forests on firm ground (35 to 40 million ha). In particular, they form a large ring around the central basin (which holds a high proportion of edaphic forests in swampy and flood-prone low-lying zones). They constitute the climax core from which a part of the semi-deciduous forests are derived, and are the far extremity of the extensive belt of Guinean equatorial rainforest that stretches east from Liberia. Typical tree species include Caesalpiniaceae such as Brachystegia laurentii, Gilbertiodendron dewevrei, G. ogoouense and Julbernadia seretii, Ebenaceae (Diospyros spp.), Olacaceae (Diogoa zenkeri and Heisteria parvifolia), Annonaceae (Isolona thonneri and Polyalthia suaveolens) and Myristicaceae such as Staudtia stipitata (trade niové). The first two species, like other Caesalpiniaceae in closed African forests (for example Monopetalanthus durandii stands in Gabon), are found in very large pure or nearly pure stands (Germain and Evrard, 1956). Gilbertiodendron dewevrei stands are also found in the Republic of the Congo and near the borders of Cameroon and the Central African Republic.

null

Low- and medium-altitude semi-deciduous moist closed forests on firm ground (Lebrun and Gilbert's "semi-deciduous mesophile forests") can be divided into three groups:

  • "Subequatorial and Guinean semi-deciduous forests" are found in or on the edges of the equatorial evergreen forest and constitute the "syngenetic stages preceding climax" ("degraded semi-deciduous moist closed forests" in Devred's classification). Typical species include Leguminosae such as Pericopsis elata (afrormosia, assamela or trade kokrodua), Copaifera soyauxii, Dialium spp., Gossweilerodendron balsamiferum (trade tola,), Oxystima oxyphyllum (trade tchitola) and Scorodophloeus zenkeri; Celtis spp. and Meliaceae such as Entandrophragma angolense (trade tiama), Guarea cedrata and G. thompsonii (trade bossé).
  • "Subequatorial and periguinean semi-deciduous forests" are climax or edaphic forests in the peripheral areas of the central basin, located in Guinean savannah areas. Typical species are Albizia zygia, Bombax flammeum, Celtis kraussiana, Cordia chrysocarpa, Lovoa trichiliodes (trade dibetou), Milletia spp. (trade wenge), Parkia spp. and Pygeum africanum. Devred distinguishes, in particular, "subequatorial and Guinean semi-deciduous moist closed Cynometra alexandri forests" covering over half a million hectares on the eastern borders of Haut-Zaïre and Kivu provinces.
  • "Zambezian semi-tropical semi-deciduous forests" constitute areas of closed forest in the midst of open forests and savannah woodlands in the south of the country. Known as muhulu, they contain a very large number of deciduous arborescent species which, together with their relatively low height (15 to 25 m), give them the appearance of dry closed forests. Typical species are Baphia bangweolensis, Brachystegia spiciformis var. schmitzii, Entandrophragma delevoyi and Manilkara spp.

Submontane and montane closed forests probably total no more than half a million hectares today and are confined to the eastern border of Kivu province. The following can be distinguished:

  • "Montane rainforests" (the Ituri ridge, the slopes of Ruwenzori, the Virunga volcanoes, the Kivu ridge, and ridges bordering Lakes Kivu and Tanganyika) typically contain conifers ( Podocarpus milanjianus, P. usambarensis and Juniperus procera) and broadleaved species such as Alangium chinense, Ekebergia ruppeliana, Ficalhoa laurifolia and Ocotea usumbarensis.
  • "Montane sclerophyllous forests" are found between 1 500 and 3 200 m, occurring either as low forests (10 to 12 m) or as varyingly open scrub (which must therefore be classified as scrub formations). Typical species are Agauria salicifolia, Erica arborea, Ilex mitis, Myrica salicifolia, Pittosporum spp. and Rapanea spp.
  • Submontane sclerophyllous forests of Grewia spp., Carissa edulis, Euphorbia calycina and E. dawei. These have practically disappeared from Burundi and Rwanda (except for the eastern part of the latter) and often occur as scrub formations.

    "Edaphic forests linked to hydromorphic soil" are extensive in the Democratic Republic of the Congo, covering about 20 million ha, primarily in the central basin. Lebrun and Gilbert distinguish the following categories:

    • "Riparian colonizing forests", low forests or shrubs with a substratum permanently or nearly permanently bathed by water without ever being properly drained. In particular, they include forest fringes of Uapaca heudelotii , which mark the transition between pioneer shrub communities and swamp or periodically flooded forests;
    • "Riparian or insular forests", with a substratum subject to alternating heavy flooding and exposure with a short drainage period, containing such species as Cleistopholis patens , Ficus mucuso , Lannea welwitschii , Oxystigma buccholzii , Pseudospondias microcarpa and Spondianthus preussi;
    • "Periodically flooded forests" with a relatively long dried-out period, of Guibourtia demeusi (trade bubinga), sometimes in pure stands or accompanied by other Caesalpiniaceae species such as Didelotia unifoliolata and Monopetalanthus pteriodophyllous and other genera such as Oubanguia , Pachystela , Parinari and Scytopetalum ;
    • "Swamp forests" with no marked period of drying out and drainage, with typical species being Alstonia congensis , Berlinia heudelotiana , Entandrophragma palustre , Mitragyna ciliata , M. stipulosa and Uapaca guineensis ;
    • "Alluvial valley forests" on alluvial banks subject to periodic flooding, with Erythrina excelsa , Khaya nyasica , Pterygota mildbraedii and Sterculia ambacensis ;
    • Mangrove forests in the Congo delta and lagoons along the Atlantic coast with the most common species being Avicennia nitida , Conocarpus erectus and Rhizophora racemosa.

    The succession of types of secondary forest that follow clearing for shifting cultivation is well described in Lebrun and Gilbert (1954), who make the following distinctions:

    • Lowland fallow and regenerated forest "corresponding to the initial shrub or arborescent stages of reconstitution or recolonization in the region of lowland closed forests" and comprising "preforest wasteland and fallow" with Caloncoba welwitschoo, Harungana madagascariensis, Trema orientalis, etc., and forest regeneration, particularly Musanga cecropioides stands;
    • Final arborescent stages of reconstitution, typically sheltering or associated with species from the original forest ("old secondary forests"), in particular with Pycnanthus angolensis (trade ilomba), and Fagara spp. in the evergreen forest zone, and Terminalia superba (trade limba) and Triplochiton scleroxylon (samba, ayous or trade obeche) in the semi-deciduous forest zone;
    • Montane regenerated and secondary forest, including preforest wasteland and fallow with small shrubs and tall grasses of the Lobelia gibberoa type, and regenerated and secondary forest with Polyscias fulva, Neoboutonia macrocalyx, Croton macrostachys, etc.
    • last updated: Monday, January 12, 2004