**4. Results**

**Figure 3.** The Interdune-depression (IDD) System with an example of the zone delineation.

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**Figure 4.** The Upland Wetland (PL) System, with an example of zone delineation.

Vegetation surveys were conducted in March 2010 following the Zurich-Montpellier (Braun-Blanquet) School of total floristic compositions approach [22]. A total of 72 sample plots (2 m The modified TWINSPAN analysis [29] resulted in the identification of 11 plant communities that can be grouped into eight major communities and six sub communities. The results of the DCA ordination for all the plant communities are contained in Figure 5. From the DCA ordination axes 1 and 2 were selected as it was the most interpretable ordination. An Eigen‐ value of 0.933 and 0.828 were obtained for Axis 1 and Axis 2 respectively.

The clay communities (communities 1 – 3) are positioned distinctly to the right of the ordination diagram. The communities which are located on predominantly sandy substrates (e.g. Community 4) are found on the extreme opposite end from the clay communities. The close proximity between Community 2 and sub community 6.2 is because both originate from the PP system. Sub communities 7.1, 7.2, and 7.3, all from the MS system, are affiliated with each other despite hydrological differences between the different zones. Sub community 5.1 and most of Community 8 originate from the PL System, explaining this association. The significant distance between sub community 5.1 (PL System) and 5.2 (IDD System) is as a result of the fact that they occur in different systems, despite similar environmental settings. Sub community 7.3 has a wide distribution, as some of its dominant species occur in other communities as well. Of these the graminoids *Stenotaphrum secundatum* and *Cynodon dactylon* are known to be variable in their habitat preference, and are not limited to a certain environment.

**Figure 5.** DCA ordination indicating clustering of communities.

#### **4.1. Substrate overlay**

Substrate has a strong influence on the spatial occurrence of vegetation communities and plant species. The clay communities (Communities 1 – 3 and 6.2) cluster strongly together with the communities occurring on duplex soil (sub communities 6.1 and some of 7.1) to a lesser degree so (Figure 6). A part of sub community 7.1 is found near the sand and high organic clusters because they are not only characterized by duplex soils, but also by higher organic matter content. The relationship between the plant species assemblages occurring on sandy and the high organic substrates are interesting, as the "High Organic" and the "Sand" communities form two overlapping clusters with a wide distribution. The "High Organic" cluster originates from Community 7 and is regarded as the "Organic MS System". This cluster is seasonally to permanently flooded, but because it originates from the MS System (which is characterized by clay lenses on the banks of the wetland) it occurs close to the cluster with the duplex substrates. Towards the bottom of Axis 2 the "Sand & High Organic" cluster contains Community 8 (seasonally and permanently flooded) (Figure 4) which originates from the sandy PL and IDD Systems.

the rest of the systems (MS, IDD & PL) (Figure 7), which obscured all other environmental distinctions between plant communities. Other differences in terms of vegetation composition could be ascribed to system characteristics such as substrate, geology, and hydrological regime. There exists no differentiation between the PL and IDD system, which is unexpected as these

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In order to elucidate the relationship between the MS, IDD & PL systems, the clay PP and DP Communities (Communities 1-3 and 6.2) were eliminated, and the data analysed again. The communities on high organic substrates with a seasonally to permanently wet hydrological

two systems are so distinct from each other.

**Figure 6.** DCA ordination with substrate overlay.

#### **4.2. Wetland system overlay**

It was hypothesized that due to the divergent characteristics and environmental settings, the five wetland systems would contain plant communities entirely unique to each system. However, the dominant division was mainly between the two clay systems (PP and DP) and

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**Figure 6.** DCA ordination with substrate overlay.

**4.1. Substrate overlay**

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**Figure 5.** DCA ordination indicating clustering of communities.

Systems.

**4.2. Wetland system overlay**

Substrate has a strong influence on the spatial occurrence of vegetation communities and plant species. The clay communities (Communities 1 – 3 and 6.2) cluster strongly together with the communities occurring on duplex soil (sub communities 6.1 and some of 7.1) to a lesser degree so (Figure 6). A part of sub community 7.1 is found near the sand and high organic clusters because they are not only characterized by duplex soils, but also by higher organic matter content. The relationship between the plant species assemblages occurring on sandy and the high organic substrates are interesting, as the "High Organic" and the "Sand" communities form two overlapping clusters with a wide distribution. The "High Organic" cluster originates from Community 7 and is regarded as the "Organic MS System". This cluster is seasonally to permanently flooded, but because it originates from the MS System (which is characterized by clay lenses on the banks of the wetland) it occurs close to the cluster with the duplex substrates. Towards the bottom of Axis 2 the "Sand & High Organic" cluster contains Community 8 (seasonally and permanently flooded) (Figure 4) which originates from the sandy PL and IDD

It was hypothesized that due to the divergent characteristics and environmental settings, the five wetland systems would contain plant communities entirely unique to each system. However, the dominant division was mainly between the two clay systems (PP and DP) and the rest of the systems (MS, IDD & PL) (Figure 7), which obscured all other environmental distinctions between plant communities. Other differences in terms of vegetation composition could be ascribed to system characteristics such as substrate, geology, and hydrological regime. There exists no differentiation between the PL and IDD system, which is unexpected as these two systems are so distinct from each other.

In order to elucidate the relationship between the MS, IDD & PL systems, the clay PP and DP Communities (Communities 1-3 and 6.2) were eliminated, and the data analysed again. The communities on high organic substrates with a seasonally to permanently wet hydrological

**Figure 7.** DCA ordination with Systems overlay.

regime (Communities 7 and 8) cluster to the left, while the communities on seasonal duplex soils and more terrestrial sandy soils (Communities 4 – 6.1) cluster to the right (Figure 8). In addition to the influence of the type of substrate on plant assemblages, there is therefore also a strong dry to wet influence.

located well outside the wetland in the terrestrial zone. Based on the standardized residuals, species in Communities 1 to 4 are underrepresented (less than -1.96) and those in communities

**Figure 8.** DCA ordination with community overlay of only the MS, PL, and IDD Systems which indicates a gradient

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The average species richness for the various systems is contained in Table 2. As in Table 1 it is clear that the clay PP and DP communities are more species poor that the rest of the wetland systems. The highly organic IDD system is significantly more species rich. Although the MS system also has high organic substrate, it contains many clay-related plant assemblages due

The plant assemblages give a good indication of the wetness levels of the various zones. Additionally the peatlands on the MCP are permanently wet, and all connected to the groundwater table [17]. This was used to assign the various plant communities to the three

5 to 8 are over represented (greater than 1.96).

from terrestrial to seasonally and permanently wet communities.

to the clay lenses on the edges of the peat substrate.

#### **4.3. Species richness**

The species richness and average species per 4m2 of each community is indicated in Table 1. The average species richness per 4m2 is clearly lower in Communities 1 – 4 (the seasonal zone of the clay wetlands) than in the rest of the communities. There was a significant association between the number of plant species and plant communities present at X2(7)=382.35, p < 0.0001. Sub communities 5.2 and 6.1 have exceptionally high species richness. The only environmental characteristic that these two sub communities have in common is that both communities are The Ecology and Species Richness of the Different Plant Communities Within Selected… http://dx.doi.org/10.5772/58219 285

**Figure 8.** DCA ordination with community overlay of only the MS, PL, and IDD Systems which indicates a gradient from terrestrial to seasonally and permanently wet communities.

regime (Communities 7 and 8) cluster to the left, while the communities on seasonal duplex soils and more terrestrial sandy soils (Communities 4 – 6.1) cluster to the right (Figure 8). In addition to the influence of the type of substrate on plant assemblages, there is therefore also

The species richness and average species per 4m2 of each community is indicated in Table 1. The average species richness per 4m2 is clearly lower in Communities 1 – 4 (the seasonal zone of the clay wetlands) than in the rest of the communities. There was a significant association between the number of plant species and plant communities present at X2(7)=382.35, p < 0.0001. Sub communities 5.2 and 6.1 have exceptionally high species richness. The only environmental characteristic that these two sub communities have in common is that both communities are

a strong dry to wet influence.

**Figure 7.** DCA ordination with Systems overlay.

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**4.3. Species richness**

located well outside the wetland in the terrestrial zone. Based on the standardized residuals, species in Communities 1 to 4 are underrepresented (less than -1.96) and those in communities 5 to 8 are over represented (greater than 1.96).

The average species richness for the various systems is contained in Table 2. As in Table 1 it is clear that the clay PP and DP communities are more species poor that the rest of the wetland systems. The highly organic IDD system is significantly more species rich. Although the MS system also has high organic substrate, it contains many clay-related plant assemblages due to the clay lenses on the edges of the peat substrate.

The plant assemblages give a good indication of the wetness levels of the various zones. Additionally the peatlands on the MCP are permanently wet, and all connected to the groundwater table [17]. This was used to assign the various plant communities to the three wetness zones indicated in Table 3. Usually species richness decrease with increasing wetness levels as few plant species are adapted to waterlogged soil [12]. However, in this study species richness in the permanently wet (therefore high organic and peat substrate) zones is actually much higher than that of seasonally wet zones.

**5. Discussion**

species richness.

**Permanently wet zone:***Lemna gibba*

**Typical plant communities:** 1, 2, 3, 6.2

**5.1. Muzi Swamp (MS) system**

**Seasonal zone:***Imperata cylindrica*

*Cynodon dactylon, Dactyloctenium aegyptium* **Typical plant communities:** 6.1, 7.1, 7.2, 7.3

**Characteristic plant species of the Muzi Swamp System**

**Permanently wet zone:***Cladium mariscus, Phragmites australis, Stenotaphrum secundatum,*

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There is a distinct division between the terrestrial zones (sub community 6.1) and the perma‐ nently and seasonally wet zones of the MS System (Community 7). The grass *Imperata cylindrica* invariably characterizes the seasonal zone (sub community 7.1); even though this zone is very closely associated with the permanently wet zones (sub community 7.2 and 7.3). This community is described in Matthews *et al.* [31]. It also correlates with the "proximalseasonally inundated floodplain" in Patrick & Ellery [30], in that it is functionally connected

The MS system is characterized by both a peat substrate which has a relatively high species richness as well as clay lenses on its edges which, in this study, has shown to have a lower

Matthews [30] describe two communities which occur on clay pans in the TEP-a "grassland on clay between thicket and pan marsh edges" Community, which does not correlate with what was found in the PP System; and a "*Nymphaea nouchali* aquatic vegetation in marshes and pans" which do correlate with the inundated zones found in the PP and DP Systems. There is a strong division between zone 1 (Community 1) and zone 2 (Community 2) of the PP System; as well as zone 1 (Community 1) and the seasonal zone 2 (Community 3) of the DP System. Community 3 is composed of many species that are regarded obligate hydrophytes such as *Marsilea sp., Pistia stratiotes*, and *Nymphaea nouchali*, yet it is regarded a seasonal zone. This classification of this community is as a result of the prominence of *Echinochloa colona* which didn't occur in open water, but in the area which is still waterlogged and able to host hydro‐ phytic species such as those named above. *Echinochloa colona* is indicative of overgrazing and

to the channel by being exposed to seasonal flood events and sedimentation.

**Characteristic plant species of the PP and DP (clay) systems (Figure 9)**

**Terrestrial zone:***Acacia nilotica, Acacia karroo, Justicia flava, Panicum maximum*

**Seasonal zone:***Cyperus fastigiatus* (PP System) & *Echinochloa colona* (DP System)

**5.2. Perched Pans (PP) and Depressions (DP) clay systems**

**Terrestrial zone:***Acacia nilotica* & *Hyperthelia dissoluta*


**Table 1.** Species richness of each community.


**Table 2.** The average species richness for the various systems.


**Table 3.** The average species richness for the various wetness levels.
