Masters Degrees (Animal, Wildlife and Grassland Sciences)

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Browsing Masters Degrees (Animal, Wildlife and Grassland Sciences) by Subject "Barko Tractor"

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    A plant ecological evaluation of mechanical bush thinning in Marakele Park, Limpopo Province
    (University of the Free State, 2008-01-19) Pienaar, Francina Christina; Smit, G. N.; Du Preez, P. J.
    English: Bush encroachment is currently of great concern in Marakele Park. The main motivation for this study, conducted during the 2003/2004 and 2004/2005 seasons, was to determine whether mechanical bush thinning, executed with a mechanical mulc her, namely the Barko Tractor, was successful in solving the bush encroachment problem in the areas where it was applied. The specific objectives of this study were to identify, describe and interpret the plant communities of a section of Marakele Park, and to establish the influences of the thinning treatments on the dynamics of the ecosystem, more specifically the regrowth and browse production of the woody plants, the species composition and dry matter (DM) yield of the herbaceous layer and the short term changes in the soil. Eight experimental plots (3 treatments, 3 controls, 2 coppice) were selected in three veld types (Acacia mellifera – Grewia flava, Combretum apiculatum – Grewia flava and Acacia erubescens – Dichrostachys cinerea), in which tree thinning was applied during 2002 and 2003. Each plot was 100 m x 200 m (20 000 m2 = 2 ha) in size. The vegetation of the plots was phytosociologically studied during the 2003/2004 season with the aid of the Braun-Blanquet vegetation sampling method. A total of 80 relevés were surveyed and upon analysis 3 major communities, 7 communities, 6 sub-communities and 3 variants were identified. The woody layer was quantified with a quantitative description technique, which is incorporated in the BECVOL-model. A step point-method and the Ecological Index Method were used to determine the species composition and veld condition of the herbaceous layer, respectively, and a harvesting method was used to determine the DM yield and the associated grazing capacity. The thinning treatments resulted in an initial decreased number of woody plants, but since no follow-up treatments were applied, a large number of new seedlings have since established and the majority of cut-plants coppiced vigorously. However, approximately three years after the thinning treatments the leaf biomass (ETTE ha-1) of the woody layer increased due to regrowth and re-encroachment to a point where negative interactions between the woody and herbaceous plants, as a result of competition for soil water and nutrients, were evident again. The species diversity of the herbaceous layer increased after the thinning treatments, but species normally associated with disturbed and overgrazed veld still dominated. It was concluded that the herbaceous layer of Marakele Park is in a poor ecological state and indications are that it is still deteriorating. The herbaceous DM yield did not respond to the thinning treatments as expected, except in areas protected from grazing herbivores. As a result, the grazing capacity of the Park was comparatively low. It is clear that Marakele Park is currently overstocked with various game species, especially of high density, selective short grass grazers. Thinning treatments will therefore not be successful unless the herbivore game numbers are reduced. Few soil variables changed significantly as a result of the thinning treatments, but in view of the fact that soil enrichment is a slow process, monitoring of the soil variables is recommended. The specific soil propertie s did, however, have a decisive influence on the vegetation type. The Combretum apiculatum – Grewia flava plots occurred on relatively shallow, gravelly soil, while the Acacia dominated plots occurred on deeper, more fertile soil. It was also concluded that the Barko Tractor, due to its size and weight, had a negative impact on the soil, mainly in the form of soil compaction. Subhabitat differentiation, rainfall and herbivory played an important role in the study area and indicated that the vegetation of Marakele Park displays both equilibrial and non-equilibrial trends. The high grazing pressure, together with the high incidence of coppice and re-encroachment of woody plants after the initial thinning treatments, as well as the lack of follow-up treatments, effectively neutralised the success of the mechanical bush thinning treatments. In order to restore these thinned areas from re-encroachment it will be necessary to cut the plants again and combine this effort with a cut-stump treatment (chemical herbicide). Due to the negative impact of the Barko Tractor, it should not be used again during any follow-up operation.