**5. Discussion**

244 International Perspectives on Global Environmental Change

**CCA 80-100cm** 

**λ λ** *r* **λ** *r* **λ** *r* **λ** *r* **λ** *r* 0.42 0.26 0.79 0.26 0.87 0.28 0.87 0.27 0.85 0.20 0.81 0.26 0.15 0.75 0.19 0.78 0.17 0.83 0.16 0.81 0.19 0.92 0.16 0.10 0.65 0.13 0.79 0.12 0.80 0.08 0.73 0.14 0.78 0.08 0.08 0.64 0.08 0.67 0.10 0.78 0.08 0.71 0.11 0.82

Table 4. Eigen values of the first four axes and the species-environment correlations.

The eigen values (λ) of the DCA and CCA were determined to further assess the degree to which the selected soil variables could explain plant species distribution in the lunette dunepan environment (Table 5). The eigen value is usually referred to as the "per centage variance accounted for" (ter Braak, 1988). It always ranges from one (1) to zero (0), and the higher the value the more important the ordination axis. Furthermore, eigen values of ca. 0.3 and higher are usually common in ecological applications (ter Braak, 1988). However, an ordination diagram that explains only a low per centage of the total variance in the species data may still be informative (ter Braak, 1988). Eigen values are usually in the form of a decreasing order with values for axes 1 and 2 being larger than those of axes 3 and 4 as is the case in Table 5 which shows the species-environment correlations (*r*) and the eigen values for the first four axes. It was observed that some eigen values were lower than 0.3 (Table 5). This suggested limitations on the use of data on selected soil variables to explain variation in plant species distribution. This was not out of the ordinary as it is widely acknowledged that plant species distribution in any ecosystem is a function of numerous environmental factors, and that it is practically impossible for any scientific research to exhaustively and concurrently incorporate all environmental factors of potential significance into a particular study. Therefore, the selected soil variables were considered sufficient to comprehensively shed light on the patterns of plant species distribution in the lunette dune-pan environment

It was established that the village of Sekoma did not originate where it was currently located. The village originated in the western side (Sekoma West) of the lunette dunes and a considerable portion of the community decided to migrate to the eastern side (Sekoma) of the lunette dunes between the years 1924-1927. However, some few members of the community decided to remain in Sekoma West and they still inhabited the area at the period of this research. They indicated that there was nothing major that caused the migration. However, observations indicated that some changes in their environment instigated the migration. For instance, observation of abandoned old hand-dug wells located in the western side of the pan suggested a possible exhaustion of underground water resources at that site. The migration implied a shift in land use pressure from one side of the lunette dune-pan complex to the other. During the discussions, it became apparent that over the years the local community had amassed a wealth of indigenous knowledge with regard to the changes in their environment. The following is an account of the perceptions of the local

The community perceived the existence of the lunette dunes in their environs as a

community pertaining to the lunette dune-pan environment:

**CCA 130-150cm**  **CCA 180-200cm** 

**CCA 40-60cm** 

**Axis DCA** 

in Sekoma.

**4.4 Social survey** 

natural phenomenon.

**CCA 0-20cm** 

#### **5.1 Pedo-geomorphology of the lunette dune complex**

Soils in the Kalahari area are sandy grains constituted mainly by quartz and small amounts of zircon, garnet, feldspar, ilmenite and tourmaline (Wang et al., 2007; Leistner, 1967). Analysis of soil properties of the Sekoma lunette dune-pan environment did not indicate otherwise as the lunette dunes were more than 95% sandy up to the depth of 200 cm. A soil profile established in one of the lunette dunes indicated no signs of soil horizons up to the depth of 200cm. This showed dominance of sand fraction in the soil texture of the lunette dunes. Goudie and Wells (1995) and Lancaster (1978) pointed out that the deflation of sediment directly from the pan floor during dry climatic condition periods resulted in the

Investigating Soils, Vegetation and Land Use in

lunette dune-pan environment.

a Lunette Dune-Pan Environment: The Case of Sekoma Lunette Dune-Pan Complex, Botswana 247

elsewhere have indicated that species that were more resistant to browsing were normally found in abundance closer to the 'foci-point', which could either be a water source or

Fig. 10. High livestock density in the Sekoma pan with lunette dunes on the background.

Herbaceous cover in the area was non-existent during the time of sampling (Figure 11). It may be argued that this could be linked to the sampling period as it was conducted at the beginning of the rainy season. However, the Kalahari communities have intrinsic inclination towards keeping cattle over small stock. On the other hand, the physiological constraints of cattle limit their movements from their water source (Moleele & Perkins, 1998; Moleele, 1999). Consequently, cattle spent most of their time within the lunette dune-pan environment (Figure 10) close to their water sources. In light of this, the intensity of land use, particularly pastoral farming, was identified as the primary contributing factor to lack of herbaceous cover in the lunette dune-pan environment. In fact, similar researches conducted elsewhere (e.g. Skarpe, 1986; Ringrose et al., 1996; Moleele & Perkins, 1998; Moleele, 1999) have indicated that the development of bare land patches is often caused by overgrazing and trampling due to high livestock density. This condition facilitated the predominance of species like *A. mellifera* and *G. flava* which have innate ability to adapt to hostile environmental conditions through their competitive edge over others (Skarpe, 1990; Moleele & Perkins, 1998; Moleele, 1999) leading to bush encroachment or thickening in the

Browse resources contribute significantly to livestock feed in environments where grazing resources are limited (Scholte, 1992; Moleele, 1999). Hence, the scarcity of grazing resources in the lunette dune-pan environment compelled livestock to heavily depend on browse resources. Scholte (1972) and Moleele (1999) indicated that the establishment and survival of woody species is determined by their survival mechanisms against browsing pressure. In view of this, plant species that had the capacity to withstand browsing pressure *(A. mellifera* and *G. flava)* became dominant in the lunette dune-pan environment over the years as land use pressure increased. Therefore, the phenomenon of environmental changes characterized

settlement area (Perkins & Thomas, 1993; Moleele & Perkins, 1998; Moleele, 1999).

formation of the lunette dunes in the Kalahari. Paradoxically, sandy soils were dominant in the lunette dunes compared to the fine textured soil associated with the pan floor. However, Lawson (1998) mentioned that presently sediment deflation from the pan floor was limited in Kalahari. Therefore, the observed soil texture suggested that the Sekoma pan had contributed insignificant amount of sediments to the development of the lunette dunes in the recent years. The dominance of the sand fraction also implied that the sandy environs of the surrounding area had recently contributed significantly to the sedimentation of the lunette dunes compared to the pan floor. This may in turn point to the spatial and temporal environmental changes that had occurred in the area with particular reference to changes in land use, and climatic conditions including, *inter alia*, direction of wind flow, rainfall patterns, increase in livestock population and occurrences of veldt fires.

Correlation analyses indicated that most of the relationships between soil and geomorphological variables were not statistically significant in the three selected lunette dunes. This suggested that the geomorphological properties, particularly the dune slope did not have an influence in the distribution of selected soil variables in the lunette dune-pan environment. Furthermore, lack of distinct patterns in the distribution trends of the selected soil variables in the lunette dune-pan environment pointed to the existence of considerable spatial heterogeneity in the soil resources distribution in the environment. Similar findings in relation to soil resources distribution in arid zones elsewhere have been cited (e.g. Wang et al., 2007; Wezel et al., 2000). Heterogeneity in soil resources in arid regions has often been attributed to the existence of resources islands that normally form under shrub canopies (Wang et al., 2007; Wezel et al., 2000). The islands usually represent micro-sites of favourable conditions for plant growth (Wang et al., 2007; Dhillion 1999).

#### **5.2 Vegetation of the lunette dune complex**

Two main plant communities that inhabited the Sekoma lunette dune-pan complex were dominated by *G. flava* and *A. mellifera*. The *G. flava* community occupied the wind ward slopes in all the sampled dunes, but also existed at the crest in the Leremela lunette dune. The *A. mellifera* community inhabited the slip face slope in all the sampled dunes, but also existed at the pan fringes in Leremela and Kebuang and at the crest in Kebuang lunette dunes. The density of *A. mellifera* was higher close to the village as compared to further afield. Leremela and Kebuang lunette dunes were the closest lunette dunes to the settlement area of Sekoma. Furthermore, the hand-dug wells used for livestock watering were located closer to Kebuang lunette dune as compared to the other two lunette dunes. Consequent to this was the evidence of pronounced land use pressure footprints on Kebuang lunette dune. Bush encroachment species predominated by *A. mellifera* was one of the prominent land use pressure footprints in the lunette dune-pan environment. Hence, land use was identified as one of the significant factors that influenced environmental changes, particularly the distribution of plant species and community composition, in the Sekoma lunette dune-pan environment.

The dominance of *A. mellifera* in the lunette dune-pan environment was indicative of the competitive capability of *A. mellifera* in areas that were subjected to intense land use pressure. The abundance of *A. mellifera* under conditions similar to that of the study site has been linked to the species morphological features which enhance its establishment and survival when subjected to harsh environmental conditions (Moleele, 1999). For instance, in spite of the high nutritive value associated with the species, its thorny nature makes it less susceptible to browsing by livestock (Tolsma et al., 1987). Similar studies conducted

formation of the lunette dunes in the Kalahari. Paradoxically, sandy soils were dominant in the lunette dunes compared to the fine textured soil associated with the pan floor. However, Lawson (1998) mentioned that presently sediment deflation from the pan floor was limited in Kalahari. Therefore, the observed soil texture suggested that the Sekoma pan had contributed insignificant amount of sediments to the development of the lunette dunes in the recent years. The dominance of the sand fraction also implied that the sandy environs of the surrounding area had recently contributed significantly to the sedimentation of the lunette dunes compared to the pan floor. This may in turn point to the spatial and temporal environmental changes that had occurred in the area with particular reference to changes in land use, and climatic conditions including, *inter alia*, direction of wind flow, rainfall

Correlation analyses indicated that most of the relationships between soil and geomorphological variables were not statistically significant in the three selected lunette dunes. This suggested that the geomorphological properties, particularly the dune slope did not have an influence in the distribution of selected soil variables in the lunette dune-pan environment. Furthermore, lack of distinct patterns in the distribution trends of the selected soil variables in the lunette dune-pan environment pointed to the existence of considerable spatial heterogeneity in the soil resources distribution in the environment. Similar findings in relation to soil resources distribution in arid zones elsewhere have been cited (e.g. Wang et al., 2007; Wezel et al., 2000). Heterogeneity in soil resources in arid regions has often been attributed to the existence of resources islands that normally form under shrub canopies (Wang et al., 2007; Wezel et al., 2000). The islands usually represent micro-sites of favourable

Two main plant communities that inhabited the Sekoma lunette dune-pan complex were dominated by *G. flava* and *A. mellifera*. The *G. flava* community occupied the wind ward slopes in all the sampled dunes, but also existed at the crest in the Leremela lunette dune. The *A. mellifera* community inhabited the slip face slope in all the sampled dunes, but also existed at the pan fringes in Leremela and Kebuang and at the crest in Kebuang lunette dunes. The density of *A. mellifera* was higher close to the village as compared to further afield. Leremela and Kebuang lunette dunes were the closest lunette dunes to the settlement area of Sekoma. Furthermore, the hand-dug wells used for livestock watering were located closer to Kebuang lunette dune as compared to the other two lunette dunes. Consequent to this was the evidence of pronounced land use pressure footprints on Kebuang lunette dune. Bush encroachment species predominated by *A. mellifera* was one of the prominent land use pressure footprints in the lunette dune-pan environment. Hence, land use was identified as one of the significant factors that influenced environmental changes, particularly the distribution of plant species

The dominance of *A. mellifera* in the lunette dune-pan environment was indicative of the competitive capability of *A. mellifera* in areas that were subjected to intense land use pressure. The abundance of *A. mellifera* under conditions similar to that of the study site has been linked to the species morphological features which enhance its establishment and survival when subjected to harsh environmental conditions (Moleele, 1999). For instance, in spite of the high nutritive value associated with the species, its thorny nature makes it less susceptible to browsing by livestock (Tolsma et al., 1987). Similar studies conducted

patterns, increase in livestock population and occurrences of veldt fires.

conditions for plant growth (Wang et al., 2007; Dhillion 1999).

and community composition, in the Sekoma lunette dune-pan environment.

**5.2 Vegetation of the lunette dune complex** 

elsewhere have indicated that species that were more resistant to browsing were normally found in abundance closer to the 'foci-point', which could either be a water source or settlement area (Perkins & Thomas, 1993; Moleele & Perkins, 1998; Moleele, 1999).

Fig. 10. High livestock density in the Sekoma pan with lunette dunes on the background.

Herbaceous cover in the area was non-existent during the time of sampling (Figure 11). It may be argued that this could be linked to the sampling period as it was conducted at the beginning of the rainy season. However, the Kalahari communities have intrinsic inclination towards keeping cattle over small stock. On the other hand, the physiological constraints of cattle limit their movements from their water source (Moleele & Perkins, 1998; Moleele, 1999). Consequently, cattle spent most of their time within the lunette dune-pan environment (Figure 10) close to their water sources. In light of this, the intensity of land use, particularly pastoral farming, was identified as the primary contributing factor to lack of herbaceous cover in the lunette dune-pan environment. In fact, similar researches conducted elsewhere (e.g. Skarpe, 1986; Ringrose et al., 1996; Moleele & Perkins, 1998; Moleele, 1999) have indicated that the development of bare land patches is often caused by overgrazing and trampling due to high livestock density. This condition facilitated the predominance of species like *A. mellifera* and *G. flava* which have innate ability to adapt to hostile environmental conditions through their competitive edge over others (Skarpe, 1990; Moleele & Perkins, 1998; Moleele, 1999) leading to bush encroachment or thickening in the lunette dune-pan environment.

Browse resources contribute significantly to livestock feed in environments where grazing resources are limited (Scholte, 1992; Moleele, 1999). Hence, the scarcity of grazing resources in the lunette dune-pan environment compelled livestock to heavily depend on browse resources. Scholte (1972) and Moleele (1999) indicated that the establishment and survival of woody species is determined by their survival mechanisms against browsing pressure. In view of this, plant species that had the capacity to withstand browsing pressure *(A. mellifera* and *G. flava)* became dominant in the lunette dune-pan environment over the years as land use pressure increased. Therefore, the phenomenon of environmental changes characterized

Investigating Soils, Vegetation and Land Use in

**7. References** 

Services.

Botswana.

Press. England.

UK.Pg 85-155.

*Environments 10, 1-12.* 

*Environments 54, 425-445.* 

*Restoration Ecology 7, 399-406.*

a Lunette Dune-Pan Environment: The Case of Sekoma Lunette Dune-Pan Complex, Botswana 249

the Sekoma area. The general changes in the climatic factors over the years had influenced changes in the land use patterns, and also contributed to environmental changes observed in the area. The predominance of bush encroachment species, particularly *A. mellifera* was evidence of the precedence of land use intensity over other drivers of environmental changes. The establishment of a sustainable environmental management strategy that could mitigate against the impacts of major drivers of environmental changes in the area was therefore necessary. The fact that the Sekoma community exhibited a wealth of indigenous knowledge in relation to the environmental changes taking place in the lunette dune-pan complex was desirable from the sustainable environmental management perspective. The findings of this study, concomitant with the indigenous technical knowledge of the Sekoma community could therefore form the basis upon which sustainable environmental management planning for the Sekoma lunette dune-pan complex could be established to facilitate natural resources and ecosystem conservation. Furthermore, attention of scientists who conduct their research works in arid environments has been drawn to the need for special consideration of lunette dune-pan complexes that normally exist as interspersed micro-ecosystems in arid environments. More studies are therefore essential to further elucidate environmental changes and ecosystem dynamics of lunette dune-pan microecosystems in arid and semi-arid zones globally. This is particularly important in view of the empirical research observations (e.g., Chanda et al., 2003; Mosweu, 2008; Mosweu & Areola, 2008) which indicated that the livelihoods of most communities living in arid and semi-arid zones revolve around the sustainability of lunette dune-pan micro-ecosystems.

Bhalotra, Y.P.R. 1985. Rainfall maps of Botswana. Gaborone. Department of Meteorological

Chanda, R., Totolo, O., Moleele, N., Setshogo, M., & Mosweu, S. 2003. Prospects for

Dhillion, S.S. 1999. Environmental heterogeneity, animal disturbances, micro site

Gauch, H.G. 1982a. Multivariate analysis in community ecology.Cambridge University

Geological Survey Department. (1995). Groundwater pollution vulnerability map of

Goldsmith, F.B. & Harrison, C.M. 1976.Description and analysis of vegetation. In: S.B

Goudie, A.S. & Thomas, D.S.G. 1986.Lunette dunes in Southern Africa.*Journal of Arid* 

Republic of Botswana. Gaborone, Botswana: Government Printers.

Cooke, R., Warren, A., & Goudie, A. 1993.Desert geomorphology. UCL Press, London Department of Surveys and Mapping .2001. Botswana National PC Atlas 1.0C. Gaborone,

subsistence livelihood and environmental sustainability along the Kalahari Transect: The case of Matsheng in Botswana's Kalahari rangelands. *Journal of Arid* 

characteristics, and seedling establishment in a *Quercushavardii* community.

Chapman. (Ed.). Methods in plant ecology.Backwell Scientific Publications, Oxford,

Bonham, C.D. 1989. Measurements for Terrestrial Vegetation.Wiley, New York.

by the development of imprints of selectivity of livestock on browse resources was inevitable in the lunette dune-pan complex.

Fig. 11. Common bare ground condition in the lunette dune-pan environment.

#### **5.3 Local community perceptions on environmental changes**

The social survey provided evidence of a wealth of indigenous knowledge that had been accumulated through informal observations and experiences by the local community. The community perceived wind as the main agent transporting soil particles from the pan and the environs onto the lunette dunes. The perceptions also indicated that the lunette dunes and the plants that grew thereon served as barriers that trapped the aeolian soil particles and lead to continuous process of dune development. The perceptions had considerable overlap with findings from empirical research (e.g. Lancaster, 1978b).

The community perceived the lunette dune-pan environment as an important water source pertinent to their pastoral farming activities. However, it was evident that potential developments in the area of pastoral farming were bedevilled by lack of grazing resources which was a major concern for the community. It was indicated that lack of grazing resources in the area was mainly caused by environmental changes that were characterized by an increase in the livestock population and a decline in the annual rainfall. Therefore, livestock grazing was perceived to be insignificant in the lunette dune-pan environment, hence the lunette dunes were considered insignificant in relation to fodder provision in Sekoma. However, field observations indicated that in spite of the changes in the environment, the lunette dune complex continued to contribute substantially in fodder provision over the years mainly through browsing resources that they sustained.
