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Title A conceptual state-and-transition model of vegetation change in the Highland Savanna: how well does the data fit it thus far?

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Short title A conceptual model for semi-arid savannas: does the data fit?

Author(s) Joubert, D.F.(1); Smit, G.N.(2)

Presenting author Joubert, D.F.

Institution(s) (1) School of Natural Resources and Tourism, Polytechnic of Namibia; (2) Dept. Animal, Wildlife and Grassland Sciences, University of the Free State, P.O. Box 339, Bloemfontein, South Africa

Keywords Acacia mellifera, fire, rainfall, seed production, competition, browsers

Abstract A conceptual state-and-transition model was developed for the Highland Savanna with emphasis on bush thickening by Acacia mellifera. Past monitoring and present experimental research focuses on the drivers of transitions between the grassy open savanna and the encroached savanna, including the role of rainfall in seed production, competition between grass and seedlings, the role of fire, and the role of small browsers. We discuss how well the results fit the conceptual model thus far. Seed production, seed germination, seedling survival in relation to rainfall have been monitored since 1998, and these data strongly show that three above average rainfall seasons are required for mass establishment. Experimental evidence is still outstanding. Preliminary results suggest that fire during the transitional period from grassy state to bushy state is essential to interrupt this transition, and that fire is not effective once shrubs have matured. Competition with climax grasses appears to not be significant at this stage and thus grass cover is unlikely to directly prevent a transition to bushy state. Small browsers such as lagomorphs might limit the density of resultant thickets. Data from experiments are still being collected.

Congress Topic Process Analysis

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