| Přispěvatelé: |
Kellner, K., Chirima, J.G., Coetzee, H.C., 10062750 - Kellner, Klaus (Supervisor), 12894451 - Coetzee, Hendrik Christiaan (Supervisor) |
| Popis: |
PhD (Environmental Sciences), North-West University, Potchefstroom Campus About 66% of rangelands in South Africa are moderately to severely degraded as a result of bush encroachment or bush thickening. Bush encroachment has nearly doubled over the past decade in many commercial, communal and conservation areas, Limpopo being no exception. Bush encroachment (increase in density of woody species) results in a temporary or permanent loss of ecosystem functions and processes and can have significant socio-ecological implications for land users since it can cause a decrease in the economic value of the land and reduces ecosystem services. To control bush encroachment and to compensate for economic losses, active and/or passive restoration methods are applied. Studies have shown that success with the restoration of bush-encroached rangelands is not only restricted to the environmental (biophysical) conditions of the rangeland but also dependent on active intervention as far as social and economic conditions are concerned. The research presented in this thesis aimed to evaluate the impacts of bush clearing and the use of brush packing restoration technique at two study sites representing two different land-use types: communal and conservation. In essence, brush packing involves covering bare degraded soil surfaces with woody branches from bushes that have been cleared in the surrounding area. Since the success of restoration projects depends on community involvement, the socio-economic benefits for local communities were also investigated. Specific objectives were, therefore, to test the effect and cost-effectiveness of brush packing as a restoration technique (1) to improve grass diversity in bush-cleared areas and (2) to improve aboveground biomass in these areas. In addition, the study set out (3) to determine whether bush clearing and restoration activities address any ecosystem services (especially those of a socio-economic nature). To test the objectives, six different non-brush packing ((1) un-cleared (control plot) (UC); (2) clearing only (CO); (3) clearing and re-seeding (CRS)) and brush packing ((4) clearing and brush packing (C-BP); (5) clearing, re-seeding and brush packing (CRS-BP); and (6) clearing, soil disturbance, re-seeding and brush packing (CSRS-BP)) treatments were compared. The treatments were replicated three times on 18 randomly distributed plots within 3 blocks and the effects compared. The results obtained from this study showed that the brush packing restoration treatments had a positive effect on improving grass species diversity particularly in the continuously grazed communal area. Grass species richness and abundance were highest for the brush packing and re-seeded treatments in the year 2019. The grass composition between the two sites were dissimilar, with the conservation site having a higher heterogeneity than at the communal site. On the other hand, a higher number of decreaser and perennial grass species were identified in the brush packing treatments particularly in the communal area. Aboveground biomass was significantly higher on the brush packing treatments than on non-brush packing treatments over the two years (2018 and 2019) at both sites. Although the total establishment costs were highest for the brush-packing treatments, this was outweighed by other positive impacts such as higher biomass production, improved grass diversity and contributions to the local community’s well-being in the form of socio-economic benefits. Brush packing undoubtedly creates a micro-environment that is favourable for the growth and recruitment of grass species. Additionally, brush packing serves as an effective protection to shield grass seedlings from grazing by livestock and/or game, thus affording grasses an opportunity for re-growth. Essentially, brush packing improves biodiversity, thereby contributing to the ecosystem services of rangeland ecosystems. It is recommended that all bush clearing and restoration projects should not concentrate on the biophysical aspects only, but take regard of the human factor as well. Furthermore, long-term studies on the permanent plots in the communal area and in the conservation area are required to investigate vegetation and diversity changes and to evaluate the effectiveness and restoration success of, particularly, bush clearing, brush packing and re-seeding restoration techniques. Doctoral |
