Multi-scale patterns and bush encroachment in an arid savanna with a shallow soil layer

Kerstin Wiegand, David Ward, David Saltz

    Research output: Contribution to journalArticlepeer-review

    122 Scopus citations

    Abstract

    Question: Bush encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and threatens the livelihood of many pastoralists. Can we derive a better understanding of the factors causing bush encroachment by investigating the scale dependency of patterns and processes in savannas? Location: An arid savanna in the Khomas Hochland, Namibia. Methods: Patterns of bush, grass, and soil nutrient distribution were surveyed on several scales along a rainfall gradient, with emphasis on intraspecific interactions within the dominant woody species, Acacia reficiens. Results: Savannas can be interpreted as patch-dynamic systems where landscapes are composed of many patches (a few ha in size) in different states of transition between grassy and woody dominance. Conclusions: In arid savannas, this patchiness is driven both by rainfall that is highly variable in space and time and by inter-tree competition. Within the paradigm of patch-dynamic savannas, bush encroachment is part of a cyclical succession between open savanna and woody dominance. The conversion from a patch of open savanna to a bush-encroached area is initiated by the spatial and temporal overlap of several (localized) rainfall events sufficient for Acacia germination and establishment. With time, growth and self-thinning will transform the bush-encroached area into a mature Acacia stand and eventually into open savanna again. Patchiness is sustained due to the local rarity (and patchiness) of rainfall sufficient for germination of woody plants as well as by plant-soil interactions.

    Original languageEnglish
    Pages (from-to)311-320
    Number of pages10
    JournalJournal of Vegetation Science
    Volume16
    Issue number3
    DOIs
    StatePublished - 1 Jan 2005

    Keywords

    • Acacia
    • Cyclic succession
    • Namibia
    • Patch-dynamics
    • Size-frequency distribution

    ASJC Scopus subject areas

    • Ecology
    • Plant Science

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