The Influence of Rainfall and Grazing on the Demography of Some African Savanna Grasses: A Matrix Modelling Approach

Size-structured matrix models were constructed for the perennial grasses of two African savannas (Aristida bipartita, Bothriochloa insculpta, Digitaria eriantha, Heteropogon contortus, Setaria incrassata and Themeda triandra) separately for each of four 1-year transitions under light or heavy grazing. The asymptotic population growth rate varied between years in relation to rainfall trends, but there were few marked differences between grazing treatments. Aristida had the highest asymptotic growth rate (λ 1 = 1.624) over a single transition period, while the heavily grazed population of Heteropogon had the lowest (λ 1 = 0.552). Most species declined in the final dry year. The stable stage distribution was generally a reversed «J» (...)