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Wageningen University (2010)

Nutrients in an African Savanna : the consequences of supply heterogeneity for plants and animals

Waal Cornelis van der

Titre : Nutrients in an African Savanna : the consequences of supply heterogeneity for plants and animals

Auteur : Waal Cornelis van der

Université de soutenance : Wageningen University

Grade : PhD thesis 2010

Résumé partiel
In savannas, trees and grasses co-exist and share resources such as water and nutrients. The ratio between the tree and grass components (i.e., vegetation structure) importantly controls productivity, animal assemblages and earth-atmosphere feedbacks. As the structure of savanna vegetation is inherently unstable and easily disturbed, finding out how the vegetation structure is controlled is of great importance for rangeland management and conservation. Currently four factors are believed to control the vegetation structure in savannas ; namely, water, nutrients, herbivory and fire. While the water and fire factors have been intensely studied, the roles of nutrients and herbivores as factors are less well known. Improving our understanding of the role of nutrients in savannas is relevant, because it is increasingly realised that global change also alter the availability of nutrients, e.g., increased nitrogen deposition. How savanna systems respond to nutrient perturbations is uncertain. Changes in soil nutrient availability are also likely to feed back to changes in forage quality, which may influence large herbivore use and vegetation impact patterns, thus indirectly influencing vegetation structure. Moreover, it is increasingly realised that not only changes in the availability of nutrients influence plants and subsequently herbivores, but also how nutrients become spatially available. In fact, new ideas suggest that differences in the scale of spatial resource heterogeneity may control how resources are partitioned between co-existing species differing in size, e.g., large trees coexisting with small grasses in savanna systems. To test how changes in nutrient availability and spatial configurations influence savanna systems, several field experiments were conducted in a semi-arid savanna in South Africa. In the study area we found that nutrient (N, P and K) availability negatively affected tree (Colophospermum mopane) seedling establishment in fertilization experiments. Also, trees failed to re-colonize nutrient-rich kraal sites that were abandoned almost half a century ago.

Mots clés : nutrients / soil fertility / heterogeneity / savannas / trees / grasses / biological competition / herbivores / grazing / browsing / foraging / vegetation / semiarid zones / scaling / nutrient availability / south africa

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Page publiée le 14 novembre 2011, mise à jour le 30 mai 2022