SHRUB LAYER DYNAMICS UNDER DIFFERENT HERBIVORE DENSITIES IN AN ARID SAVANNA, BOTSWANA

In areas with no and moderate cattle grazing, shrub densities fluctuated but showed no consistent change, while density increased with heavy grazing. After 5 yr, density, cover, total mass, shoot and leaf mass and leaf area of shrubs were higher in the area under heavy grazing than in those under no or moderate grazing. There were no differences in shrub abundance between ungrazed and moderately grazed areas. The increase in shrub abundance with heavy grazing was accounted for by 2 of the 5 recorded species, Acacia mellifera and Grewia flava. Both are shallow rooted suggesting that they were favoured by an increase in water availability in the surface soil following overgrazing of the grass layer. -from Author