Trends in savanna structure and composition along an aridity gradient in the Kalahari

Abstract

Abstract. The Kalahari sand sheet occupies 2.5 million ha in southern Africa. It is an area with relatively similar deep aeolian soils, and a strong south to north gradient in rainfall, from 200 to 1000 mm mean annual precipitation (MAP) in the region studied. This provides an excellent basis for gradient studies at the subcontinental scale. This paper briefly reviews the literature on the vegetation of the Kalahari and describes the vegetation structure and composition at 11 new sites. There is a clear gradient in woody plant biomass (as indexed by basal area) from south to north. Above the minimum level of 200 mm MAP, the woody basal area increases at a rate of ca. 2.5 m2.ha‐1 per 100 mm MAP. Mean maximum tree height also increases along the gradient, reaching 20 m at ca. 800 mm MAP. The number of species to contribute > 95% of the woody basal area increases from one at 200 mm to 16 at 1000 mm MAP. Members of the Mimosaceae (mainly Acacia) dominate the tree layer up to 400 mm MAP. They are replaced by either the Combretaceae (Combretum or Terminalia) or Colophospermum mopane of the Caesalpinaceae between 400 and 600 mm MAP, and by other representatives of the Caesalpinaceae above 600 mm MAP. The vegetation is largely deciduous up to 1000 mm MAP, except for species that apparently have access to groundwater, which may be locally dominant above about 600 mm MAP.

Soil carbon and nitrogen dynamics in southern African savannas: the effect of vegetation-induced patch-scale heterogeneities and large scale rainfall gradients

“…The KT is one of a set of IGBP (International Geosphere-Biosphere Programme) "megatransects" identified for global change studies (e.g., Koch et al 1995;Scholes et al 2002). Owing to its relatively uniform, deep sandy soils (Wang et al 2007), the KT provides an ideal setting to investigate changes in ecosystem structure and function (including C or nutrient cycling) along a spatial precipitation gradient while minimizing the confounding effects of soil heterogeneity (Shugart et al 2004).…”

Combined effects of soil moisture and nitrogen availability variations on grass productivity in African savannas

“…The KT is one of a set of IGBP (International Geosphere-Biosphere Programme) "megatransects" (Koch et al 1995;Scholes et al 2002) identified for global change studies. The KT traverses a dramatic aridity gradient on relatively homogenous soils (deep Kalahari sands), offering an ideal setting to study nutrient and vegetation dynamics without confounding soil effects (Wang et al 2007a).…”

Characterization of Structural Composition and Diversity of Vegetation in the Kpashimi Forest Reserve, Niger State, Nigeria

“…Such knowledge, is however required in order to expand the understanding of ecosystem processes (Hahn, 1996), to relate vegetation maps to ecological properties (Devineau, 2001), and as a basis for modelling approaches (Brown & Gaston, 1996;FAO, 2001). Furthermore, the dearth of data quantifying tree physiognomies restricts our understanding of the regional and global impacts of ecological changes in savannas (Scholes et al, 2002). In this context the research question is stated thus: Which floristic composition and vegetation structure occur in different vegetation types found in the study area?…”