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Accueil du site → Doctorat → Royaume-Uni → 1996 → The regeneration dynamics of arid Acacia tortilis woodland formations, Northern Kenya : dry woodland vegetation and nomadic pastoral society in transition

University of Oxford (1996)

The regeneration dynamics of arid Acacia tortilis woodland formations, Northern Kenya : dry woodland vegetation and nomadic pastoral society in transition

Moss, Jonathan M S.

Titre : The regeneration dynamics of arid Acacia tortilis woodland formations, Northern Kenya : dry woodland vegetation and nomadic pastoral society in transition.

Auteur : Moss, Jonathan M S.

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (Ph.D.) : 1996

Résumé
Natural woodland formations in dryland areas of eastern Africa are recognised to play a vital role in the patterns of land use and livelihoods of significant population of pastoral and semi-pastoral peoples. There is considerable debate, however, as to the effects of recent socio-economic trends (sedentarisation, reduced mobility, population growth) on woody vegetation (Chapter 1). The woodland formations of the north Chalbi study area, Marsabit District, are of vital importance to Gabbra pastoralists whose resource utilisation patterns are increasingly constrained. Woody vegetation is subject to a complex process of compositional, structural and distributional change (Chapter 2). On the basis of aerial photography and a comprehensive vegetation survey, changes since 1957 are described and quantified (Chapter 3). A wide range of possible factors are considered, woodland utilisation rates are quantified, and the regeneration potential of Acacia tortilis assessed. On most sites woodland dynamics are largely a function of livestock density and herd mobility. Livestock promote woody regeneration but beyond critical limits suppression by browsing prevents successful recruitment. An increase in the frequency of severe droughts is identified as the critical factor in woodland decline on drought-sensitive soils (Chapter 4). Extensive regeneration process experimentation allows the identification of critical factors that determine regeneration rates (Chapter 5).Results enable significant contribution to our understanding of disequilibrium ecosystem dynamics and the relative importance of compositional determinants. Furthermore the fundamental adequacy of the increasingly prevalent disequilibrium paradigm is considered. While the quintessential role of the magnitude and frequency of critical levels of climatic disturbance is widely recognised, species composition and developmental stage are also critical in dry woodland ecosystem dynamics. Implications with respect to Acacia tortilis nursery practice and natural woodland management strategies for the promotion of regeneration and recruitment are discussed (Chapter 6).

Annonce : EThOS (UK)

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