**5. Discussion**

258 Ecosystems Biodiversity

The following boxplot uses the medians and quartiles to compare the distributions of biomass (kg DM/ha) of the plots by grazing type (non-grazed; exclosure plots; grazed)

As expected there is some overlap in the values of the grazed and exclosure plots, the latter only being fenced off for the past 12 months, while the non-grazed plots have some overlap with the exclosure plots. Thus although there appear to be differences between the grazed and exclosure plots the overlap results in there being a non-significant

Although overlaps exist, differences between the different treatments are observed indicating that the non-grazed Platberg peatlands have the highest production followed by the exclosure plots that show variable increases within the short time (12 months) since

> Boxplot by Group Variable: Biomass (kg DM/ha) Median 25%-75% Min-Max

exclosure grazed never grazed Grazing

Fig. 7. Boxplots of the medians and quartiles comparing the biomass of the different grazing

The Kruskal-Wallis ANOVA by Ranks test was used to compare the Biomass (kg DM/ha) of the plots by grazing type. From the Kruskal-Wallis test [H ( 2, N=17)=12.071 p =.0024] it shows that there is a significant difference in the ranks of the plots categorised by grazing type (Table 2). Significant differences were found between the grazed, non-grazed and exclosure plots. By using the the Mann-Whitney U Test on the ranked data the significant differences were found to be between the grazed and non-grazed plots (p<0.01) and

**4.5 Biomass per grazing type** 

difference between them.

being fenced off, compared to the open grazed plots.

(Figure 7).


types.

1000

2000

3000

Biomass (kg DM/ha)

4000

5000

6000

7000

0

#### **5.1 Species composition and richness**

Two distinctive vegetation communities resulted from the data classification namely the Platberg and Lesotho peatlands respectively (Table 1). Each unit reflects the homogeneity of the communities in terms of plant species composition and dominance. In all wetlands the forbs (including geophytes, succulents and sedges) comprised the largest percentage of species with grasses the lowest. The uniqueness of each unit can be ascribed to various physical factors such as altitude, pH, moisture regime of the peat, and biotic impact.

Studies done by Sieben et al. (2010) revealed that typical wetland plants cannot cope well with the cold conditions during winter months. This opens several niches for forbs, especially species that are not dominant in lowland wetlands to become dominant in high altitude wetlands. The forb *Ranunculus meyeri* (Species group B - Table 1) is such a species, which occur across all altitudes but are dominant in high-altitude wetlands (Sieben et al., 2010). This species was found to be prominent in the Lesotho peatlands.

The peat deposits vary in depth from shallow 10 cm to over 2 m deep (Kuenene, 2008). The peatlands are covered by short mat-like peat forming plants. Dominant species in the Lesotho peatlands include the grass *Pentaschistis oreodoxa*, the sedge *Isolepis cernua*, the geophyte *Rhodohypoxis deflexa*, and the forbs *Haplocarpa nervosa, Cotuls radicalis* and *Ranunculus meyeri* (Table 1). Unlike the Lesotho peatlands, the platberg peatlands are mainly grassland dominated with the grasses *Andropogon appendiculautus* and *Pennisetum sphacelatum* prominent. The sedge *Ficinia stolonifera* and the grass *Helictotrichon longifolium* are locally dominant (Table 1).

Waterlogged conditions are a requirement for peat formation. Peat formation is a very slow process and is mainly formed from the root decay of vascular plants that grow on the peatlands. This process takes place in the absence of oxygen. Anoxia or reduction conditions between and below the roots, decomposes the dead material to form amorphous peat. According to the species composition of the wetlands at Khalong-la-Lithunya, Koti-Sepola, and Kao, sedges such as *Isolepis cernua* are together with forbs such as *Haplocarpha nervosa*, and *Ranunculus meyeri* the main contributors to peat formation. In contrast at Platberg the grasses *Andropogon appendiculatus, Pennisetum sphacelatum* and *Helictotrichon longifolium* are the main contributors to peat formation.

Impact of Domestic Animals on Ecosystem Integrity of Lesotho High Altitude Peatlands 261

seems as though the long-term grazing of these systems has affected the species composition. The average species richness for the Platberg peatlands (11.4) is lower than the Lesotho peatlands (17.5). The higher richness in the Lesotho peatlands can be ascribed to greater habitat diversity as a result of various environmental factors resulting in the formation of peat and thurfur on the peatland surface as well as its short structure. In contrast the dense and tall grass tufts of the Platberg peatlands have a shading effect on the lower stratum of the herbaceous layer. This could prevent various forb species from establishing that could explain the lower species richness found. Brown & Bugg (2001) also found that established perennial grasses inhibited the growth of seeded forbs. There are also no thurfur present within the Platberg peatlands with its more homogeneous

It is generally believed that overgrazing is one of the most important factors causing vegetation degradation (Danckwerts & Tainton, 1996; David et al., 2000). Furthermore it could influence the hydrological status, stability and productivity of the ecosystem (Kirkman & Moore, 1995; O'Connor & Bredenkamp, 1997; Snyman & Fouché, 1991; Snyman 1997, 1998). Biomass is a good indicator of available forage and the risk of soil erosion (Schino et al., 2003). Biomass is dependent on the root reserves, nutrient and water content of the soil. Overgrazing can negatively affect the species composition and especially biomass production leading to a decrease in resilience of the ecosystem (Carpenter et al., 2001). This is evident from the results of this study where a significant difference was found between the production of the non-grazed Platberg peatlands compared to the grazed and exclosure plots in Lesotho indicating the negative effect of long-term grazing on these peatlands. The grasses in the recently erected exclosures (12 months ago) of the Lesotho peatlands show an increase in production compared to the grazed plots with some overlap with the non-grazed plots of Platberg (Figures 3, 4 & 6). Although not statistically significant at this stage the exclosure plots appear to have a higher production and it is expected that the difference may only become significant with a larger sample size and with continued monitoring over a longer term. This also correlates with the lower height levels of the plants in these plots compared to the exclosure plots. Structurally the Platberg peatlands are much taller with an average height of 51 cm compared to the short Lesotho peatlands with and average height ranging between 1.5 and 6 cm. The near pristine peatlands of Platberg had on average a much higher production and canopy cover with no signs of erosion. The exclosure plots of the Khalong-la-Lithunya peatland had similar biomass values than the Platberg peatlands

The grasses in the exclosure plots showed a higher production (598.6 kg DM/ha – 8% of total biomass) than the grasses in the grazed plots (68.6 kg DM/ha – 2.6% of total biomass). It therefore appears that where grazing is absent that the grasses could become more prominent exerting a greater influence on the vegetation thereby causing a future change in

The Platberg peatlands have a higher amount of energy stored (due to the higher biomass) than the degraded Lesotho peatlands also meaning that it has a higher carbon storage

indicating that if grazing is decreased production will increase.

species composition.

ecosystem functioning.

habitat.

**5.2 Effects of grazing on biomass** 

A characteristic of these peatlands is the frost-induced mounds or thufur (Figure 8). Backéus & Grab (1995) and Grab (1994) investigated these thufur and concluded that their morphological changes can be correlated to the changing environmental state of the peatlands. These thufur are present on hill slope seeps and valley head fens. The species composition of these thufur differs from the surrounding wetland vegetation and can be attributed to a relatively lower moisture content. Species that dominate the thufur at the study sites are *Helichrysum bellidiastrum, Athrixia fontana*, and *Sebaea marlothii*.

Fig. 8. Frost-induced mounds or thufur (mounds), with a different species composition (insert) present on the peatlands.

Another characteristic of these peatlands are the open water pools or tarns. The typical vegetation is floating-leaved and submergent aquatic vegetation. Dominant species present in these open water bodies are the grass *Colpodium drakensbergensis*, the forbs *Crassula natans, Lagarosiphon muscoides*, and *Limosella maior* were found at Khalong-la-Lithunya, Kao and Koti-Sephola.

The catchment slopes are characterised by shallow soils and a relatively high percentage of surface rock. The soil has a relatively low organic content due to the high runoff onto the peatlands that has resulted in degraded vegetation and coarse soil texture.

Extensive grazing depletes the root and canopy reserves of perennial grasses (Carpenter et al. 2001) which are then replaced by annual and other forb species. This will have a negative impact on the resilience of the system to maintain its ecosystem functions such as water storage, nutrient cycling and production. In the Lesotho peatlands the forbs comprise the largest percentage (86-87%) of the species composition, while in the Platberg peatlands there is a more even species composition (42% grasses and 58% forbs). Thus, it seems as though the long-term grazing of these systems has affected the species composition. The average species richness for the Platberg peatlands (11.4) is lower than the Lesotho peatlands (17.5). The higher richness in the Lesotho peatlands can be ascribed to greater habitat diversity as a result of various environmental factors resulting in the formation of peat and thurfur on the peatland surface as well as its short structure. In contrast the dense and tall grass tufts of the Platberg peatlands have a shading effect on the lower stratum of the herbaceous layer. This could prevent various forb species from establishing that could explain the lower species richness found. Brown & Bugg (2001) also found that established perennial grasses inhibited the growth of seeded forbs. There are also no thurfur present within the Platberg peatlands with its more homogeneous habitat.

#### **5.2 Effects of grazing on biomass**

260 Ecosystems Biodiversity

A characteristic of these peatlands is the frost-induced mounds or thufur (Figure 8). Backéus & Grab (1995) and Grab (1994) investigated these thufur and concluded that their morphological changes can be correlated to the changing environmental state of the peatlands. These thufur are present on hill slope seeps and valley head fens. The species composition of these thufur differs from the surrounding wetland vegetation and can be attributed to a relatively lower moisture content. Species that dominate the thufur at the

study sites are *Helichrysum bellidiastrum, Athrixia fontana*, and *Sebaea marlothii*.

Fig. 8. Frost-induced mounds or thufur (mounds), with a different species composition

Another characteristic of these peatlands are the open water pools or tarns. The typical vegetation is floating-leaved and submergent aquatic vegetation. Dominant species present in these open water bodies are the grass *Colpodium drakensbergensis*, the forbs *Crassula natans, Lagarosiphon muscoides*, and *Limosella maior* were found at Khalong-la-Lithunya, Kao and

The catchment slopes are characterised by shallow soils and a relatively high percentage of surface rock. The soil has a relatively low organic content due to the high runoff onto the

Extensive grazing depletes the root and canopy reserves of perennial grasses (Carpenter et al. 2001) which are then replaced by annual and other forb species. This will have a negative impact on the resilience of the system to maintain its ecosystem functions such as water storage, nutrient cycling and production. In the Lesotho peatlands the forbs comprise the largest percentage (86-87%) of the species composition, while in the Platberg peatlands there is a more even species composition (42% grasses and 58% forbs). Thus, it

peatlands that has resulted in degraded vegetation and coarse soil texture.

(insert) present on the peatlands.

Koti-Sephola.

It is generally believed that overgrazing is one of the most important factors causing vegetation degradation (Danckwerts & Tainton, 1996; David et al., 2000). Furthermore it could influence the hydrological status, stability and productivity of the ecosystem (Kirkman & Moore, 1995; O'Connor & Bredenkamp, 1997; Snyman & Fouché, 1991; Snyman 1997, 1998). Biomass is a good indicator of available forage and the risk of soil erosion (Schino et al., 2003). Biomass is dependent on the root reserves, nutrient and water content of the soil. Overgrazing can negatively affect the species composition and especially biomass production leading to a decrease in resilience of the ecosystem (Carpenter et al., 2001). This is evident from the results of this study where a significant difference was found between the production of the non-grazed Platberg peatlands compared to the grazed and exclosure plots in Lesotho indicating the negative effect of long-term grazing on these peatlands. The grasses in the recently erected exclosures (12 months ago) of the Lesotho peatlands show an increase in production compared to the grazed plots with some overlap with the non-grazed plots of Platberg (Figures 3, 4 & 6). Although not statistically significant at this stage the exclosure plots appear to have a higher production and it is expected that the difference may only become significant with a larger sample size and with continued monitoring over a longer term. This also correlates with the lower height levels of the plants in these plots compared to the exclosure plots. Structurally the Platberg peatlands are much taller with an average height of 51 cm compared to the short Lesotho peatlands with and average height ranging between 1.5 and 6 cm. The near pristine peatlands of Platberg had on average a much higher production and canopy cover with no signs of erosion. The exclosure plots of the Khalong-la-Lithunya peatland had similar biomass values than the Platberg peatlands indicating that if grazing is decreased production will increase.

The grasses in the exclosure plots showed a higher production (598.6 kg DM/ha – 8% of total biomass) than the grasses in the grazed plots (68.6 kg DM/ha – 2.6% of total biomass). It therefore appears that where grazing is absent that the grasses could become more prominent exerting a greater influence on the vegetation thereby causing a future change in species composition.

The Platberg peatlands have a higher amount of energy stored (due to the higher biomass) than the degraded Lesotho peatlands also meaning that it has a higher carbon storage ecosystem functioning.

Impact of Domestic Animals on Ecosystem Integrity of Lesotho High Altitude Peatlands 263

vegetation also dies off due to the high urea-content of the urine of animals (Figure 11), while cow dung covers the vegetation for a significant period of time causing the exclusion of sunlight, which put the affected plants under stress leading to die off of the vegetation

Fig. 11. Vegetation die-off caused by the high urea content of the urine of domestic stock

Fig. 12. Cow dung covers the vegetation for a significant period of time also leading to

Footpaths (Figure 9) are another major contributor to wetland degradation. On footpaths the animal hooves usually cause destruction of the vegetation cover which in turn results in the

vegetation die-off with other species establishing.

formation of large erosion gullies.

with other species establishing (Figure 12).

grazing on the peatlands.
