Anthropo-zoogenic impact on the structure and regeneration of a submontane forest in Kenya

Abstract

Reasons for the degradation of submontane forest (c80km2) in one of the National Parks in which a rhino sanctuary has recently been established in the Salient of the Aberdare Naitonal Park were investigated. Vegetation changes have been principally initiated by humans and intensified or maintained by large mammals. Shifting cultivation and livestock grazing have led to the widespread destruction of primary forest. Since the gazetting of the National Park (1950), secondary bushland has developed on previously settled land (c25km2); to date, no recolonization by forest has taken place, although considerable regeneration has been observed in adjacent forests. The structure and composition of the present forest vegetation suggests that most forests are secondary. Forests containing Juniperus procera are subjected to selective felling of the emergent trees which, in the absence of fire, will develop into Cassipourea forest. Primary, or little-disturbed, forest was only found in the higher parts of the Upper Salient. The present herbivore density however, does seem to impede the regeneration of forest in areas covered by secondary bushland. Here, the tree seedlings are often exposed to browsing and trampling pressure after the removal of fallen trees by man. This, in combination with the slow growth of trees above 1920m, seems to be responsible for the lack of regeneration. The shrub-density of the vegetation of the glades seems to be dependent mainly on herbivore densities, in turn controlled by drought, disease and predators. Fire has played only a minor role in the Salient since the cessation of shifting cultivation. -from Author