Changes in vegetation cover in northern Chobe National Park (Botswana) were assessed using aerial photographs from1962,1985 and1998, with subsequent ground proofing. In addition, cumulative browsing by elephants and the occurrence of ¢re scars were recorded on random vegetation sites within shrubland (n 20) and mixed woodland (n 20). Coverage of woodland vegetation decreased from 60% to 30% between 1962 and 1998, while shrubland vegetation increased from 5% to 33% during the same period. During the study period, woodland has gradually retreated away from the river front. While riparian forest covered a continuous area along the riverfront in 1962, only fragments were left in 1998. We found a signi¢cant decrease in browse use with increasing distance to the Chobe river for Combretum apiculatum, Combretum elaeagnoides, Combretum mossambicense and other woody plants combined (all P < 0.0001). The occurrence of ¢re (P < 0.0001) and basal area (P < 0.0001) were positively related to distance to the river. Elephant browsing occurred on >70% of available stems within 2 km from the river, while less than 20% of the trees had ¢re scars in the same zone. Beyond 7 km from the river, elephant browsing was reduced to >50% of available stems, while more than 50% of the trees had ¢re scars. The density of any of the shrubs was not related to distance to the river neither within shrubland (all P > 0.05) nor within mixed woodlands (all P > 0.05).La densite¨d'aucunarbuste n'e¨tait lie¨e a© la distance jusqu'a© la rivie© re, ni dans la zone arbustive (ensemble P > 0.05) ni dans la zone arbore¨e me¨lange¨e (ensemble P > 0.05).

No abstract

Northern Botswana and adjacent areas, have the world's largest population of African elephant (Loxodonta africana). However, a 100 years ago elephants were rare following excessive hunting. Simultaneously, ungulate populations were severely reduced by decease. The ecological effects of the reduction in large herbivores must have been substantial, but are little known. Today, however, ecosystem changes following the increase in elephant numbers cause considerable concern in Botswana. This was the background for the "BONIC" project, investigating the interactions between the increasing elephant population and other ecosystem components and processes. Results confirm that the ecosystem is changing following the increase in elephant and ungulate populations, and, presumably, developing towards a situation resembling that before the reduction of large herbivores. We see no ecological reasons to artificially change elephant numbers. There are, however, economic and social reasons to control elephants, and their range in northern Botswana may have to be artificially restricted.