Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The ecology of large herbivores in Hell’s Gate National Park, Naivasha, Kenya.

Auteur : Kiringe John Warui.

Université de soutenance : University of Leicester

Grade : Doctor of Philosophy (PhD) 1993

Résumé partiel
This study sought to determine the population size, density, distribution, habitat utilization and biomass of large herbivores in Hell’s Gate National Park and two neighbouring ranches, Kedong and Kongoni. The study further determined primary production and wildlife grazing in the Park grassland, the effects of wildlife on the vegetation around the Park’s artificial water troughs and the effects of Maasai livestock and geothermal prospecting on the Park vegetation. Herbivore counts were carried out in Hell’s Gate National Park and the two neighbouring ranches between February 1990 and April 1992. Kongoni, zebra and Thomson’s gazelle were found to be the most abundant species. The distribution pattern exhibited by the ungulates in the three areas was neither random or regular, and appeared to be influenced by both topography and vegetation type. Dry and wet season distribution patterns of the wildlife were similar. In the three study areas, most of the herbivores were found to prefer the grassland followed by relatively open shrubland. Areas of dense vegetation and rugged terrain were not preferred. Kongoni, zebra, eland and buffalo contributed the highest proportion of the herbivore biomass. They contributed 82% of the total herbivore biomass in the Park, 85% in Kedong Ranch and 82% in Kongoni Ranch. The herbivore biomass fluctuated monthly depending on population fluctuations, such that when there was a high count of the herbivores in a given month, there was a corresponding high biomass. Above-ground primary production and herbivore grazing were estimated in the Park grassland which was the main grazing area for most of the ungulates. There were two peaks of primary production which coincided with the occurence of the long and short rains, such that there was a significant linear regression between net primary production and rainfall. The monthly amount of dead and live grass biomass fluctuated in response to seasonal rainfall, such that during the dry season the amount of dead biomass increased while that of the live biomass decreased and vice versa during the wet season. There was a significant linear regression of live grass biomass on rainfall, but there was no significant correlation between rainfall and dead grass biomass. The annual productivity of the grassland was 720g/m2/yr, and the total annual offtake of the grass forage by the herbivores was 12.7%. Therefore, most of the grass forage dried up to form dead biomass which was probably of little food value to the wildlife

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