Declaration 2 Publications and manuscripts
3.2 Material and Methods
3.2.1.1 Veld condition assessment
During November and December of 2010, the benchmark method developed by Foran et al.
(1978) and Tainton et al. (1980) was used to assess the rangeland condition of five study sites,
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four of which were in the sub-wards of the Okhombe communal rangelands whilst the fifth site was within the Cathedral Peak conservation area. These five sites included degraded areas (Mpameni and Ngubhela), rehabilitated areas (Mpameni and Ngubhela), and one conserved area (Cathedral Peak). The benchmark method involves measuring the composition of the plant species and then comparing that measurement to a reference benchmark site which is characterised by grassland of excellent condition (Tainton et al., 1980). The benchmark for the present study area was the Moist Highland Sourveld Group 8 (Foran et al., 1978; Tainton et al., 1980). The motivation for using this procedure was to evaluate the rangeland condition based on species count (Oluwole and Dube, 2008). The procedure also shows if the rangeland has been optimally grazed, under-grazed or overgrazed, and it furthermore reveals the degree of degradation (Hardy and Hurt, 1989). The vegetation assessment was conducted on sampling areas of conserved, rehabilitated and degraded land using the point sampling method described by both Tainton et al. (1980) and Trollope et al. (1990). This method was used to determine the composition of grass species to provide a precise measure of relative grass abundances in each site. Two transect lines, each 200 m long, were established at each site. The nearest living plant to the point of a metal spike was identified and recorded for 200 points. This sample size was shown to be sufficient to evaluate the veld (Hardy and Tainton, 2007). At each transect, elevation, slope and GPS coordinates were recorded. The observed grass species were classified into their species categories (i.e. Decreaser, Increaser I, Increaser II and Increaser III). The condition of a sample of veld was calculated by comparing the species composition of the particular site with that of the benchmark (Camp, 1997).
3.2.1.2 Basal cover
Basal cover for each sample site was determined using paired observations of the mean distance and mean basal diameter of the tufts (Hardy and Tainton, 2007; Oluwole and Dube, 2008). All the techniques that have been used to monitor grassland quality and quantity in South Africa require an estimate of basal cover (Hardy and Tainton, 2007). This is because grass basal cover is well adapted to specific growth conditions and will increase or decrease dramatically if these conditions change (O'Connor et al., 2001; Snyman and Fouché, 2007). Basal cover data were collected by using a measuring tape and a metal spike. The distance from the nearest living plant to the point of a metal spike was then measured (D), and the basal diameter of the tuft (d) was
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identified, measured and recorded for 100 points (Hardy and Tainton, 2007). Basal cover was calculated using the following equation, as developed by Hardy and Tainton (2007):
Where BC is basal cover, D is the mean distance (cm) from a point to the nearest tuft, and d is the mean basal diameter (cm) of the tuft.
3.2.1.3 Species diversity index
Species diversity is the number of different species in a particular place (Beisel and Moreteau, 1997; Borda-de-Água et al., 2002; Magurran, 1988; Shackleton, 2000). It is used as an indicator of rangeland degradation (Metzger et al., 2005; Rutherford and Powrie, 2010). This is because both plant quantity and quality decline with heavy grazing (Metzger et al., 2005; Rutherford and Powrie, 2010). Shannon‟s diversity index, which was developed by Shannon & Weaver (1963), has been widely used within the ecological field. It is a nonparametric statistical technique for establishing species diversity, which is the proportion of species relative to (qi) the total number of species (Q) (Chao and Shen, 2003; Lande, 1996). The use of Shannon‟s diversity index was preferred in this study because it is suited to the comparison of different ecosystems. In this study, Shannon‟s diversity index was applied to degraded, rehabilitated and conserved sites at Okhombe and Cathedral Peak during November and December of 2010. The nearest plant to 200 random points along a transect line was identified and recorded. Species diversity was calculated by considering the number of species per ecological category (decreaser species, increaser I, increaser IIa, increaser IIb, increaser IIc, and increaser III). The equation for computing species diversity is as follows (Shannon and Weaver, 1963):
Where H' is the Shannon-Weaver diversity index, qi is the fraction of individuals belonging to the i species, Q is the total number of the individual species in the sample, and S is species richness.
BC = 19.8+0.39( D )-11.87(log e D )+0.64( d )+2.93(log e d ) (1)
(2)
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Grassland species evenness was measured by Pielou‟s equation (Pielou, 1966), where evenness (E) is represented as follows:
E = H/ ln S (3)
Where H' is the Shannon-Weaver diversity index and S is the number of species within the community.
3.2.1.4 Soil assessment
Soil samples were collected from 56 sites (18 non-degraded, 19 rehabilitated and 19 degraded).
Soil samples were collected under dry atmospheric conditions, and care was taken to ensure that these sites were representative of their respective ecosystems. Field borders, ditch banks and burn sites were therefore avoided (Maitima and Olson, 2001). Soil samples were taken using a soil-sampling auger to a depth of 15 cm. A field label was written on each sample bag, which included soil sample plot number, species names, elevation, slope, and GPS coordinates. All the labelled bags were stored in dry conditions until they were transported to the laboratory for analysis. Soil samples were analysed for soil fertility. P was measured using a photometer, while K, Ca, Mg, Zn, Mn and Cu were determined using electrothermal flame atomic absorption spectrometry. The N and organic carbon were both measured by mid-infrared spectroscopy. Soil pH was measured with a pH meter. The soil density was measured using a 10 ml scoop.
The data were analysed statistically using one-way ANOVA in the GenStat (version 12) statistical software package (Payne, 2009) to determine whether or not there were any significant differences between the different soil classes. Least significant differences (LSDs) (P < 0.05) were calculated to separate the means of the soil properties.