Theses and Dissertations

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Browsing Theses and Dissertations by Subject "Biomass"

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    Evaluation of the effectiveness of manual clearing methods and reseeding techniques in restoring Pteronia incana encroached communal rangelands.
    (University of Fort Hare, 2024) Makanya, Monelisi; Jama, K.; Mndela, M.
    Pteronia incana encroachment is a form of land degradation, particularly in communal rangelands of the Eastern Cape, South Africa. This species displaces the herbaceous layer, thus reducing species diversity, plant cover, and rangeland productivity. Soil chemical properties determine the efficacy of herbaceous restoration by affecting plant growth. In efforts to revert the adverse effects of shrub encroachment, a study was conducted to assess the effects of topography and P. incana canopy cover on soil chemical properties, and the effectiveness of different restoration techniques on the success of herbaceous vegetation recovery, diversity and the nutritive value of grasses. A 25-m2 square plots having a 10m interspacing were marked based on shrub encroachment levels (SELs) namely: 1) open grasslands, 2) moderate, and 3) heavily encroached, with each SEL replicated three times in lower, middle and upper slopes in the north and south facing slope aspect. Soil samples were collected at a 20-cm depth at the four corners and the centre of plot, and then were analysed for N, P, K, OC, Ca, Mg, Zn, Cu, Mn, pH, and total cations. Thereafter, the following restoration treatments were applied on each 10-m2 square plot: 1) uprooting and reseeding (UPR), 2) uprooting only (UPO), 3) cutting and reseeding (CR), 4) cutting only (CO), and 5) untreated control (CTL), with each treatment replicated three times in north and south slope aspects. The shrub was cleared either by uprooting or cutting and the cleared plots were reseeded with a grass mixture of Panicum maximum and Eragrostis curvula seeds. Five 0.25 m2 quadrats were sampled per plot in four corners and centre of each experimental plot. Afterwards the plants within the quadrat were identified, calculated and their diameters were measured using a standard ruler. The vegetative cover was visually estimated from the quadrats before harvesting the herbaceous plant biomass. The collected data was used to determine plant density, richness and diversity. The nutritive value of reseeded grasses was analysed using an NIR spectrometer. The results revealed that the interactive effects of SEL and topography (p < 0.05) were only significant on Zn content with open grasslands in the upper slope position having two-fold higher Zn content than other encroachment levels in the same position. The interaction between the slope aspect and slope position (p < 0.05) significantly affected soil N, P, C, Mg, Zn, Mn pH, and cations. The N and OC in the lower slope in the north was significantly (p < 0.05) higher than in the lower slope in the south aspect. The upper slope in the south aspect had significantly (p < 0.05) higher P and Ca than the middle slope. The Mg was higher on the lower slopes on both slope aspects, but the upper slope in the north had higher Mg than the upper slope in the south slope aspect. Zinc increased with slope position in the south aspect and the opposite was true for the north slope aspect. Slope position alone significantly affected Cu, with the upper slope having higher Cu content. Soils were slightly acidic, and total cations were higher on the south-facing slope. The results on herbaceous recovery indicated that graminoid cover was highest in all treatments compared to the control, with CR exhibiting relatively higher cover in both north and south facing slopes. Restoration treatments independently affected plant density, richness and diversity, with these parameters being lowest in the control relative to other treatments. Slope aspect, treatment, and species interacted significantly (p = 0.029) on herbaceous biomass production (BP), with CO in the north aspect attaining two-fold higher BP of non reseeded grasses compared to other treatments. Responses of reseeded species varied by slope aspect, with P. maximum attaining two-fold higher BP in CR and UPR in the north than the south slope, whereas E. curvula had higher BP in CR in the south than the north slope. Furthermore, the results revealed that the nutritive value of grasses was significantly affected by the independent effect of slope aspect and species. The north-facing slope aspect had significantly (p < 0.05) higher CP, ash, Ca, and P than the south slope aspect, except for NDF. Similarly, P. maximum had significantly (p < 0.05) higher CP, ash, Ca, and P than E. curvula. CP had a positive significant (p < 0.05) relationship with Ca (r = 0.69) and P (r = 0.68). Although the energy and ADF were not significantly (p > 0.05) affected by slope aspect and species, they had a negative significant (p < 0.05) relationship with each other (r =-0.56). Overall, the study found that P. incana encroachment had no significant effect on soil chemical properties, with topography being the primary driver of variation in soil chemical properties. Shrub clearing proved beneficial in restoring plant diversity and density, regardless of the method, reseeding, and slope aspect. However, biomass, canopy cover, and basal cover responses were influenced by slope aspects. Thus, it is suggested that the decision on restoration method should be guided by herbaceous vegetation indicators of restoration priority.