Preliminary root atlas for Zimbabwe and Zambia

Abstract In vegetation types experiencing a prolonged dry season, available soil moisture over the year is the most important factor in their ecology .A range of rooting strategies for the various woody species present has evolved to overcome or circumvent this seasonal moisture deficiency, yet little work has been published from south central Africa (with the exception of that by Savory (1963a,b) which is not now readily available) describing the rooting structures of the major woodland species. Walter (1979) describes a hypothesis, developed further by Walker and Noy-Meir (1982) and Walker et al. (1982), whereby in dry woodlands and savannas grasses exploit the moisture in the superficial soil layers making maximum use of incident rainfall, while woody plants utilize soil moisture at deeper layers and so are not directly competing for moisture with the grass layer; This hypothesis can be developed further concerning the rooting strategies of woody species. Some are principally surface rooting (e.g. Combretum celastroides, Baphia massaiensis) and can give rise to thicket vegetation, while others (e.g. Baikiaea plurijuga) are very deep rooting and survive through the year on moisture accessible at depth. Aggressive species (e.g. Brachystegia) can exploit moisture in both deep and shallow layers of the soil. A knowledge of the rooting strategies adopted by various species would, in conjunction with details on soil type and depth, greatly assist in understanding their distribution, ecology and management. For example, on Kalahari sand soils differences in rooting strategy appear to explain satisfactorily observed phenological behaviour, and deep-rooted tree species are generally restricted to sites on deep sands. Endean (1968) and Calvert (1986) take this further and provide an explanation of the structural differences between Baikiaea and miombo woodlands based on rooting patterns and niche availability.