The influence of different land use types on plant species diversity, composition and vegetation structure in the Kalahari woodlands of Salambala conservancy, north-east Namibia
Loading...
Date
2007
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Human societies have, for centuries, impacted and altered the natural environments through different land use practises. Unsustainable land use practices are seen as one of the major threats to biodiversity around the globe. Therefore, the main objective of this study was to assess the impacts of different land use types, mainly grazing and browsing by wildlife and livestock; land clearance for cultivation and wood harvesting on plant species diversity, composition and vegetation structure in the Kalahari woodlands of the Salambala conservancy in northeast Namibia. Three areas representing the different land use types were compared. These were the core, transitional and outside areas, which represented low, medium and high land use intensities, respectively. The nested plots design method was used to determine the minimal plot area. Trees (stem diameter 15cm) were assessed in 20m*20m plots, shrubs (stem diameter 15cm) were assessed in 5m*5m subplots and grasses and forbs were assessed in 1m*1m subplots. The structural attributes measured were tree basal circumference (cm), tree and shrub height, woody cover (line-intercept method) and visual estimation of grass cover. The range condition was assessed based on decreaser-increaser method. Plant species diversity and richness were significantly higher in the core and transitional areas. The hierarchical cluster analysis (HCA) recognised three main floristic associations. These are, Combretum collinum mixed tall-sparse woodland, Combretum collinum-Terminalia sericea tall-dense woodland and Combretum collinum woodland thicket corresponding to the land use types in the core, transitional and outside areas respectively. The Detredend Correspondence Analysis (DCA) showed that 44.3 of the total variation in species composition was accounted for along the first axis, which was mainly associated with land use intensity. Tree density and total basal area were significantly higher in the transitional area; and higher in the core than the outside area, although not statistically supported. Stem density and woody cover were higher in the outside area. Grass cover was higher in the core area, but did not differ between the transitional and outside areas. Basal area and height class distribution differed significantly among the three sites. Shrub and forb densities did not differ significantly among the sites. The range condition in the core area was classified as selectively grazed (50); 40 selectively and 40 overgrazed in the transitional area and 86 overgrazed in the outside area. Plant species diversity, richness and composition are clearly being negatively impacted by the different land use types, evident from significantly low diversity and richness in the highly utilised outside area. The effect of land use on species composition is more pronounced in the herbaceous layers, contributing more to the separation of the vegetation by the classification and ordination methods. There is clear evidence that the different land use types are gradually transforming Kalahari woodlands in the Salambala conservancy from woodlands to woodland thickets. The effects of past land use in the conservancy could also be linked to the current structure and composition of the vegetation. Future studies and research programmes especially in communal area conservancies, should take into consideration the assessment of the status of vegetation and other components of biodiversity, as well as carrying capacity and stocking rates of the range.
Description
Submitted in partial fulfilment of the requirements for the degree of Master of Science in Biodiversity Management and Research in collaboration with Humboldt- Universität zu Berlin
Keywords
Biological diversity, Plant diversity, Biological diversity conservation