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 â Grewia flava, Combretum apiculatum â Grewia flava and Acacia erubescens
â 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 â 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-01192007-132945 |
| Date | 19 January 2007 |
| Creators | Pienaar, Francina Christina |
| Contributors | Dr PJ du Preez, Prof GN Smit |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-01192007-132945/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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