Primary production of a grassland in Nairobi National Park, Keny

Abstract

(1) Net aerial primary production of a grassland in Nairobi National Park was estimated using the harvest method in conjunction with estimates of mortality in the three most abundant grass species. (2) As a result of the long rains (March-April) net primary production (dry matter) was 651 g m-2 and as a result of the short rains (October-December), 420 g m-2. These estimates were more than twice the peak biomass observed in each season. (3) The three most abundant grass species differed in their performance. Themeda triandra Forsk. had the highest net production relative to its biomass and the highest mortality rate in all seasons. Pennisetum mezianum Stapf. was lowest in both these respects and Setaria phleoides Leeke intermediate. (4) Removal by large herbivores was too small to detect by exclosure methods. Calculations based upon population density of these animals suggest that they consumed less than 4% of annual net primary production. (5) The grassland studied was fairly typical of others with similar rainfall in East and southern Africa with respect to peak herbaceous biomass and average large herbivore population density. (6) Some implications of these results for management of the park are discussed