Characteristics of dry forest in West Africa and the influence of fire



Abstract. The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data from Ghana show that these forests have two-peak annual rainfall between 850 and 1350 mm, with 6–10 dry months (< 100 mm rain) each year; by relatively nutrient-rich soils developed over a variety of rock types; by short stature (tallest trees 10-40 m) relatively high deciduousness in the upper canopy and evergreenness in the understorey; and by a distinctive flora which changes gradually towards areas of higher rainfall but abruptly at the forest-savanna boundary. Dry forests near the forest-savanna boundary form a distinctive sub-type as a result of occasional encroachment by litter fires which have become more common in the 1980's.

Evidence is presented to suggest that many parts of the forest zone in West Africa may have been subject to fires most often in the dry forest types. Past fires are likely to have had a profound influence on the composition of the present forest canopy. Fire mortality is greatest in small trees, whilst drought (without fire) kills more large trees. This thinning process allows rapid recolonisation especially by Marantaceous and Zingiberaceous forbs and by pioneer trees. Seedlings of canopy trees grow beneath these colonising plants. Recurrent fires seriously impede the recovery of burnt forest and are a principal concern for the rehabilitation of dry forests.