Soil Factors Affecting the Distribution of the Grassland Types and their Utilization by Wild Animals on the Serengeti Plains, Tanganyika

Abstract

Seven soil/vegetation associations are described and analytical data for the soil presented. These are 1. Juvenile Soils on volcanic ash; Dactyloctenium/Sporobolus dune country. 2. Calcimorphic Soils with hard-pans; Sporobolus/Kyllinga short grasslands. 3. Calcimorphic Soils with soft-pans; Cynodon/Sporobolus intermediate grasslands. 4. Vertisols of lithomorphic origin; Pennisetum/Andropogon long grasslands. 5. Brown Calcareous Soils; Themeda/PennisetunTlong grasslands. 6. Vertisols of lithomorphic origin in the south; Pennisetum/-Cynodon medium grasslands. 7. Associations on Kopjes. Both soil and vegetation patterns form a gradient from east to west, with the more mature soils supporting the taller and denser grasslands. Parent material, climate and time factors have all acted to produce increasingly mature soils westward, though all are fully saturated within 6 ft (1.8 m) of the soil surface. Wind erodability, depth, texture and salt concentration are crucial in deciding the water storage capacity of the soils and the availability of moisture to plants. As a results they largely determine the distribution, growth habit and vigor of the grass species. Levels of available N, Mn and Mg may play a minor role. Vegetational variations within each soil/grassland association can be explained either by grazing and burning patterns or more locally on the basis of the catena. It is unlikely that a nutrient factor is causing the apparent seasonal preference of game for the shorter grassland areas. Growth stage and palatability of the grasses, when water is available, are considered to be the main reasons for this, but the degree of soil poachability also plays a part.