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

Titre : Large herbivores and process dynamics in a managed savanna ecosystem

Auteur : Augustine David J.

Université de soutenance : Syracuse University

Grade : Doctor of Philosophy (PhD) 2002

Présentation
Feedbacks between soil nutrients, plant communities, and large mammalian herbivores were studied at the Mpala Ranch and Research Centre in Laikipia, Kenya. The landscape consists of short-grass glades, typically 0.5-1.0 ha in size, dispersed throughout the dominant Acacia bushland vegetation. I examined (1) whether glades are created through the use and abandonment of overnight cattle corrals or ’bomas’, (2) the importance of these glades as habitat for native and domestic ungulates, (3) feedback effects of herbivores on aboveground herbaceous productivity (ANPP) and soil nutrient dynamics, and (4) effects of climatic variability on herbivore abundance and soil-grass-grazer interactions.
All soil characteristics measured across a boma-glade chronosequence indicate glades are indeed derived from abandoned bomas. In particular, soil N, P and organic matter quality in the surface (0-15 cm) layer were similar for glades and 30-39 year old bomas, but were enriched relative to surrounding bushland. Soil texture was similar for bomas, glades, and bushland, indicating glades were not derived from a unique parent material. Cynodon leaves from bomas and glades were highly enriched in P, Ca and N relative to Cynodon from nearby bushland sites. Local abundance of impala, zebra and eland was closely tied to the distribution of nutrient-rich glades. Seasonal analyses of impala habitat selection suggested that selection for glade habitat was related both to predation risk and the availability of mineral-rich forage. In particular, P in boma and glade grass was above recommended levels for growing and lactating ruminants, while P content of bushland grass was lower than recommended levels.

Mots-clés : Nitrogen cycling, Savanna, Ungulates, Phosphorus

Résumé de la thèse