Abstract
The dry woodland and savanna regions of the Okavango Delta form a transition zone between the Okavango Swamps and the Kalahari Desert and have been largely overlooked in terms of vegetation classification and mapping. This study focused on the species composition and height structure of this vegetation, with the aim of identifying vegetation classes and providing a vegetation map accompanied by quantitative data. Two hundred and fifty-six plots (50 m × 50 m) were sampled and species cover abundance, total cover and structural composition were recorded. The plots were classified using agglomerative, hierarchical cluster analysis using group means and Bray-Curtis similarity and groups described using indicator species analysis. In total, 23 woody species and 28 grass species were recorded. Acacia erioloba and Colophospermum mopane were the most common woody species, whilst Urochloa mossambicensis, Panicum maximum, Dactyloctenium gigantiumand Eragrostis lehmanniana were the most widespread grasses. Eleven vegetation types were identified, with the most widespread being Short mixed mopane woodland, Tall mopane woodland and Tall mixed mopane woodland, covering 288.73 km2 (28%), 209.14 km2 (20%) and 173.30 km2 (17%) of the area, respectively. Despite their extensive area, these three vegetation types were the least species-rich, whilst Palm thornveld, Short mixed broadleaf woodland and Open mixed Acacia woodland were the most taxonomically variable. By contrast, Closed mixed Acacia woodland and Closed Acacia–Combretum woodland had the most limited distribution, accounting for less than 1% of the mapped area each.Conservation implications: The dry woodland and savanna vegetation of the Okavango Delta comprises a much wider suite of plant communities than the Acacia-dominated and Mopane-dominated classifications often used. This classification provided a more detailed understanding of this vegetation and essential background information for monitoring, management and research.
Highlights
De Cáceres and Wiser (2011:387) state that, ‘Vegetation classification is a useful tool for basic and applied research as well as for environmental management.’ The major goal when conducting such an exercise is to simplify a complex continuous pattern of change in vegetation composition and structure across the landscape in order to understand how species are distributed and why, as well as to predict how species, communities and landscapes will respond to environmental changes (Symstad 2002)
The cluster analysis and similarity profile test (SIMPROF) test produced groups, which were significantly different from one another (p < 0.05)
The two most widespread woody species occurring in varying densities in every vegetation type were A. erioloba and C. mopane, whilst the most widespread grass species were U. mossambicensis, P. maximum, D. gigantium and
Summary
De Cáceres and Wiser (2011:387) state that, ‘Vegetation classification is a useful tool for basic and applied research as well as for environmental management.’ The major goal when conducting such an exercise is to simplify a complex continuous pattern of change in vegetation composition and structure across the landscape in order to understand how species are distributed and why, as well as to predict how species, communities and landscapes will respond to environmental changes (Symstad 2002). Current vegetation mapping practices are strongly influenced by the availability of remote-sensing tools (Bredenkamp et al 1998). One of the more efficient methods for the construction of multipurpose vegetation maps is a floristic-based classification, supported by multivariate analysis and structural data (Dias, Elias & Nunes 2004). This allows the classification to be used to investigate both long-term change indicated by the floristic composition and shortterm change indicated by the structural composition (Lux & Bemmerlein-Lux 1998). Vegetation maps and descriptions can be used for a range of purposes such as: landscape planning, http://www.koedoe.co.za doi:10.4102/koedoe.v55i1.1100 development and implementation of management plans, forestry, conservation, monitoring and many varied forms of research (Bredenkamp et al 1998; Dias et al 2004)
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