170 species of plants have been found in the Lamto savannas, 129 of which belong to the herb layer. The most abundant families are the Gramineae (27.9 % of the species), the Cyperaceae (17.8 %) and the Leguminosae (16.2 %). The percentage of the various lifeforms is as follows : Therophytes, 43.5 % ; Hemicryptophytes, 36.1 % ; Geophvtes, 11.1 % and Chamaephytes, 8.2 %. Various associations are described, but two main vegetation types are recognized : the Andropogon savanna on well drained tropical ferrugineous soils and the Loudetia simplex prairie on black clays. The yearly cycle of the grass biomass is described in burnt and unburnt savannas (figures 7 and 8) : the primary production is estimated to be between 25 and 30 tons of plant tissues (fresh weight) per hectare per year — out of which 76 % are imputable to the grass layer, 15 % to the bush layer and 9 % to the tree layer.