Spatial and temporal landscape patterns in arid and semi-arid African savannas

Abstract

Landscape pattern in arid and semi-arid savannas of sub-Saharan Africa is determined primarily by soil moisture and edaphic properties of soils. Savannas are patterned by densely wooded riverine and lacustrine forests and by more sparsely wooded seasonal drainages and moist bottoms. Alterations in soil chemistry properties create intense vegetation patterns, either by increasing soil fertility or by decreasing soil salinity and alkalinity in infertile or saline environments. Fire and disturbances by large herbivores are generally secondary in importance to soil properties in creating landscape patterns and regulating landscape dynamics. In relatively pristine grassland communities in national parks and wildlife refuges, animal disturbances and fire scars are often revegetated by species that are already abundant in the surrounding communities, creating short-lived pattern. Only where disturbances seriously alter soil-moisture and edaphic properties or where fire and elephants create grassland-woodland mosaics is the pattern longer-lived. The effects of large mammals on landscape pattern are intensified when animal concentrations are compressed into small game reserves by human settlement or when boreholes are constructed for wildlife and livestock. Artificially high herbivore densities lead to overgrazing, erosion and grassland deterioration, creating a pattern that is large-scale and long-lived. -from Author