Effects of large herbivores and fire on the regeneration of Acacia erioloba woodlands in Chobe National Park, Botswana

Abstract

Acacia erioloba woodlands provide important forage and shade for wildlife in northern Botswana. Mortality of mature trees caused by browsing elephants has been well documented but the lack of regeneration of new trees has received little attention. Annual growth of new shoots and changes in height were measured to determine the influence of elephants and small ungulate browsers, rainfall and ï¿ re on the growth and survival of established A. erioloba seedlings from 1995 to 1997 in the Savuti area of Chobe National Park. All above-ground vegetation was removed from 40% of established seedlings in 1995 and 28% in 1997 by browsing elephants, and the mean height of remaining seedlings decreased from >550 mm to <300mm.When seedlings browsed by kudu, impala and steenbok but not elephants are considered, mean seedling height increased <50mm per year, even though mean new shoot growth remaining at the end of the dry season was 100^200mm. Fires burned portions of the study area in1993and1997, killing above-ground vegetation, but most established A. erioloba seedlings survived, producing coppice growth from roots. While elephants and ï¿ re caused the greatest reduction in established seedling height and number, small browsers suppressed growth, keeping seedlings vulnerable to ï¿ re and delaying growth to reproductive maturity.