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Accueil du site → Doctorat → Namibie → Rooting strategies of savanna shrubs in the Kalahari basin : Implications for the coexistence of woody and herbaceous plants and shrub encroachment in the African savannas

University of Namibia (2020)

Rooting strategies of savanna shrubs in the Kalahari basin : Implications for the coexistence of woody and herbaceous plants and shrub encroachment in the African savannas

Nakanyala, J.

Titre : Rooting strategies of savanna shrubs in the Kalahari basin : Implications for the coexistence of woody and herbaceous plants and shrub encroachment in the African savannas

Auteur : Nakanyala, J.

Université de soutenance  : University of Namibia

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
The savanna biomes are characterised by a coexistence of two antagonist – woody plants and herbaceous plants in defiance of competition theories. Scientific efforts to understand this unique coexistence are still largely inconclusive ; various theories have been proposed, but no unanimous theoretical framework exists to date. Among these theories, the root niche-partitioning model offers the most popular, yet the most controversially debated viewpoint. It argues that this coexistence is a result of vertical root niche-partitioning, a natural mechanism by which woody plants develop deeper root systems to avoid competition with herbaceous plants. Despite its prominence and subsequent integration into models of species coexistence and arid eco-hydrology, several shortcomings of this model are evident. For example, it overlooks the critical issue of root plasticity. This study was thus designed to investigate the root systems of various savanna shrubs across a rainfall gradient in the Kalahari to test the aforementioned model. The overall aim was to investigate, compare, and contrast the root system architecture (RSA) of encroaching shrubs and those of non-encroaching shrubs within the proximate environmental setting. Using a direct excavation method, 183 shrubs were sampled, had their roots exposed and were subjected to morphometric measurements. Shrub encroachers were randomly selected and four non-encroaching shrubs surrounding each of the sampled encroacher plant were systematically chosen, using the nearest-neighbour approach. Results indicated that shrubs in the Kalahari develop diverse root system architecture which exhibits significant inter- and intra-species plasticity. In particular, three bush encroaching shrubs

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