**3. Results**

#### **3.1. Local climate trends**

**Figures 3** and **4** show a graphical representation of annual rainfall totals and temperature. Generally, the vlei area experiences low rainfall and high temperatures. The average annual rainfall total is 544.38 mm. The total annual amount of rainfall has been decreasing between 1962 and Assessing the Drivers of Wetland Changes in Areas Associated with Wildlife-Based Tourism… http://dx.doi.org/10.5772/intechopen.80513 175

**Figure 3.** Annual rainfall totals for Dete Vlei, Hwange district (1962–2016).

Services Department of Zimbabwe. Local climate data were used to assess the possible effect of local climate variability on wetland vegetation condition and geomorphic processes such

**Point name X coordinate Y coordinate** A 26.98 −18.66 B 27.00 −18.66 C 27.02 −18.65 D 27.05 −18.64 E 27.07 −18.64

Historical information of the wetland's geomorphic condition was obtained from purposively sampled key informants targeted for semi-structured interviews. In this case, a template with open-ended questions was prepared to guide face-to-face discussions. The key informants were selected from organisations that are involved in photographic safari ventures, management of the forest areas located in the catchment area of the vlei or individuals who had knowledge of the area stretching over several decades. The key informants were the Safari Operators, former Forest Commission Divisional Manager for Indigenous Forests, Matabeleland North Forestry Commission Provincial Manager, Sikumi Forester and the Parks and Wildlife Management Authority Ecologist. Records of wildlife population changes

Rainfall and temperature data obtained from the Meteorological Services Department of Zimbabwe used for determining trends were subjected to regression analysis performed in Microsoft Office Excel 2007. Trend analysis was done to determine if there was change in mean annual temperature (minimum and maximum) and annual rainfall totals, since temperature and rainfall amount influences vegetation cover and geomorphic processes such as erosion and deposition. Qualitative data generated through semi-structured interviews (on perceived changes in wildlife numbers, vlei's condition and climate trends) were analysed using thematic analysis method [22]. Wildlife population density was calculated basing on average game counts done by Forestry Commission in 2016 and the vlei size measured in ha.

**Figures 3** and **4** show a graphical representation of annual rainfall totals and temperature. Generally, the vlei area experiences low rainfall and high temperatures. The average annual rainfall total is 544.38 mm. The total annual amount of rainfall has been decreasing between 1962 and

as erosion and deposition.

**Table 1.** Location of the selected slope sampling points.

174 Wetlands Management - Assessing Risk and Sustainable Solutions

**2.5. Data analysis**

**3. Results**

**3.1. Local climate trends**

and number of tourists were also obtained and reviewed.

**Figure 4.** Annual minimum and maximum temperature for Dete Vlei, Hwange district.

2016 (y = −2.932x + 672.800; r2 = 0.033). The highest (975.9 mm) and lowest (311.9 mm) amount of rainfall were received in 1973 and 2000, respectively. In contrast, mean maximum yearly temperature (y = 0.035x + 28.350; r2 = 0.219) and the mean minimum yearly temperature (y = 0.019x + 12.910; r2 = 0.059) have been increasing between 1962 and 2010. The mean maximum yearly temperature is 29.1°C, whereas the mean minimum yearly temperature is 13.3°C (**Figure 4**). The former Forest Commission Divisional Manager for Indigenous Forests attributes the reduction in rainfall to changing climate accompanied by frequent droughts that intensified from the year 2000.

#### **3.2. Wildlife population changes**

The common wildlife species found in the vlei are elephants, buffaloes, baboons, sables, impalas, kudu and warthogs (**Figure 5**). Generally, small and large predators account for relatively

Salt licks are evident in the lower section of the vlei and are characterised by several pits and areas devoid of vegetation (**Figure 7**). Other than pumped water, artificial salt licks appear to be attracting many different wildlife species during the dry season. This explains why high numbers of large mammals such as elephants, buffaloes and plains game are found in the lower section of the vlei throughout the year. This situation is in sharp contrast with the upper section of the vlei without salt licks where evidence of bare areas was not noted at all based on the SPOT satellite images (**Figure 6**). On average, salt licks of 3 m diameter and 35 cm depth are found in several parts of the lower wetland section. Field observation results showed that vegetation cover was completely lost in

**Bare area in the lower section** 

**of the vlei**

1984 316 467.6 783.6 0 0 0 0 2007 348.8 429.7 778.5 13.32 3.1 0 0 2013 446.2 456.9 903.1 21.12 4.6 0.82 0.002

whereas the widest pit was 8 m in diameter. Interviews with key informants revealed that some safari operators apply salt, especially in areas near the artificial water sources, in order to attract more wildlife for game viewing. Salt licking is assumed to have started in

**Figure 6.** Saptio-temporal changes in erosional features and bare area linked to water holes in Dete vlei (1984–2013).

around the salt licks (**Figure 7**). The deepest salt lick pit was 83 cm,

**Erosional features in the lower section** 

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177

**of the vlei**

**Area (ha) % Area (ha) %**

Assessing the Drivers of Wetland Changes in Areas Associated with Wildlife-Based Tourism…

areas as wide as 800 m2

**Year Upper Lower Total vlei** 

**size**

**Table 2.** Proportion of bare area (ha) and erosional features in the vlei.

**Figure 5.** Wildlife species population between 2013 and 2016 (Source: Forestry Commission [9]).

few of the total number of animals found in the vlei as they are significantly outnumbered by herbivores, categorised as grazers, browsers or both. Large mammals such as elephants and buffaloes frequent the wetland for water and/or grazing. The elephant population is the highest, with an average of 469 over the last 4 years (2013–2016), whereas buffaloes have the second highest number of large mammals, with an average of 302.

Key informants indicate that plain game species such as impala, kudu, duiker, waterbuck and eland were also a common feature of the wetland landscape. Although game count statistics obtained from the Forestry Commission show that the population of different wildlife species has been fluctuating over the past years, in contrast, baboon populations have been increasing. The interviewed Ecologist and Forester indicated that the present wildlife population exceeds the carrying capacity of the area as evidenced by grazing pressure in some parts of the wetland. The elephants destroy trees on the edges/fringes of the wetland indicated by dominance of trimmed trees. The pressure on grazing has resulted in bare areas (**Figure 6**).

#### **3.3. Wetland erosion linked to wildlife**

**Figure 6** shows that the wetland's lower section has erosional features such as developing gullies and is losing vegetation in areas surrounding artificial watering points and salt licks.

Spatio-temporal analysis of land cover shows that there is no bare area in the upper section of the vlei between 1984 and 2013. In contrast, the areas devoid of vegetation as a result of wildlife trampling and erosional features occupy 5% of the overall extent of the lower section of the vlei (**Table 2**). The bare area around artificial watering points and salt licks increased by 58.56% between years 2007 and 2013. They now cover 4.6% of the lower section of the vlei used for photographic safaris. Erosional features such as gullies, not present in the whole wetland during the previous years, occupied about 0.82 ha in the lower section of the wetland in 2013 (**Figure 6**; **Table 2**); a sign that geomorphological disturbances such as erosion were taking place. The overall spatial extent of the upper section of the wetland increased by 41.2%, whereas the lower section with artificial water points and salt licks shrunk by −2.3% between 1984 and 2013.


**Table 2.** Proportion of bare area (ha) and erosional features in the vlei.

few of the total number of animals found in the vlei as they are significantly outnumbered by herbivores, categorised as grazers, browsers or both. Large mammals such as elephants and buffaloes frequent the wetland for water and/or grazing. The elephant population is the highest, with an average of 469 over the last 4 years (2013–2016), whereas buffaloes have the

Key informants indicate that plain game species such as impala, kudu, duiker, waterbuck and eland were also a common feature of the wetland landscape. Although game count statistics obtained from the Forestry Commission show that the population of different wildlife species has been fluctuating over the past years, in contrast, baboon populations have been increasing. The interviewed Ecologist and Forester indicated that the present wildlife population exceeds the carrying capacity of the area as evidenced by grazing pressure in some parts of the wetland. The elephants destroy trees on the edges/fringes of the wetland indicated by dominance of trimmed trees. The pressure on grazing has resulted in bare areas (**Figure 6**).

**Figure 6** shows that the wetland's lower section has erosional features such as developing gullies and is losing vegetation in areas surrounding artificial watering points and salt licks. Spatio-temporal analysis of land cover shows that there is no bare area in the upper section of the vlei between 1984 and 2013. In contrast, the areas devoid of vegetation as a result of wildlife trampling and erosional features occupy 5% of the overall extent of the lower section of the vlei (**Table 2**). The bare area around artificial watering points and salt licks increased by 58.56% between years 2007 and 2013. They now cover 4.6% of the lower section of the vlei used for photographic safaris. Erosional features such as gullies, not present in the whole wetland during the previous years, occupied about 0.82 ha in the lower section of the wetland in 2013 (**Figure 6**; **Table 2**); a sign that geomorphological disturbances such as erosion were taking place. The overall spatial extent of the upper section of the wetland increased by 41.2%, whereas the lower section with artificial water points and salt licks shrunk by −2.3% between 1984 and 2013.

second highest number of large mammals, with an average of 302.

176 Wetlands Management - Assessing Risk and Sustainable Solutions

**Figure 5.** Wildlife species population between 2013 and 2016 (Source: Forestry Commission [9]).

**3.3. Wetland erosion linked to wildlife**

Salt licks are evident in the lower section of the vlei and are characterised by several pits and areas devoid of vegetation (**Figure 7**). Other than pumped water, artificial salt licks appear to be attracting many different wildlife species during the dry season. This explains why high numbers of large mammals such as elephants, buffaloes and plains game are found in the lower section of the vlei throughout the year. This situation is in sharp contrast with the upper section of the vlei without salt licks where evidence of bare areas was not noted at all based on the SPOT satellite images (**Figure 6**). On average, salt licks of 3 m diameter and 35 cm depth are found in several parts of the lower wetland section. Field observation results showed that vegetation cover was completely lost in areas as wide as 800 m2 around the salt licks (**Figure 7**). The deepest salt lick pit was 83 cm, whereas the widest pit was 8 m in diameter. Interviews with key informants revealed that some safari operators apply salt, especially in areas near the artificial water sources, in order to attract more wildlife for game viewing. Salt licking is assumed to have started in

**Figure 6.** Saptio-temporal changes in erosional features and bare area linked to water holes in Dete vlei (1984–2013).

not vicious to humans. Given the fact that each of the lodges receives more than 200 visitors per fortnight during the dry season, some walking paths often used by tourists to get closer to the watering points are gradually developing into rills and gullies and there is evidence of deposition in the vlei as shown in **Figure 8**. Gully development seems to be further influenced by fairly steep gradient, which on average is 4% (**Table 3**). Point D with the steepest slope has

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Moreover, two weirs were excavated in the lower section of the wetland in the late 1980s to impound more water for photographic safari activities. Coincidentally, weir construction and boreholes drilling started at the same time when additional lodges were established. However, there is evidence of soil erosion on some of the weirs. Erosion is as a result of overtopping of the weirs during the rainy, especially during the years when high rainfall was received in the area. The eroded sediments are likely to increase sediment yield downstream, which may be

There is a gravel road constructed along the vlei to facilitate easy game drive by tourists around the wetland area. The gravel road has drains which control and discharge runoff into the vlei at certain points. Channelized flow is discharged into the wetland resulting in gully erosion, especially where vehicles use unplanned drive ways to cross the vlei during the dry season. Unplanned drive ways in the vlei result in vegetation loss and defined channels

severe if high rainfall persists, since rainfall in the area is highly variable (**Figure 8**).

a more pronounced gully.

**Figure 8.** Gully development along tourists' foot paths.

**Slope point Slope angle**

**Table 3.** Slope gradient at selected interval along the vlei, in percentages.

Point A 2.4 Point B 4.1 Point C 3.9 Point D 5 Point E 3.8 Average 3.8

**Figure 7.** Section of the vlei altered by wildlife during salt licking.

the mid- to late 1990s in order to control the introduced Presidential Elephants, protected under a presidential decree of 1990 but instead the licks are attracting different wildlife species.

During the dry season when there is water shortage in the area, safari operators pump ground water from the wetland into open waterholes. These artificial watering points replenished by boreholes were established in the late-1980s across the lower section of the wetland, in proximity to lodges (**Figure 3**), to attract more wildlife for game viewing. Trampling is evident within 15 m around watering points as a result of large number of wild herbivores that drink water from these sources.

Due to high movement and frequency of wild animals in the vlei, mainly for water and salt licking, a number of wildlife trails or paths have been formed. Wild animals' trails are possibly facilitating the formation of several rills across the wetland area, especially in the lower section. The wildlife paths facilitate concentrated water flow, hence promoting soil erosion and siltation or sediment delivery into the wetland. Pressure on grazing by wild herbivores is a common phenomenon mainly around salt licks and watering points. Key informant interviewees attributed the grazing pressure to high wildlife populations and the presence of grazers around water points. This is more pronounced during the dry season due to physical water scarcity in the natural pans dotted around the forest area and in the adjacent Hwange national game park.

Meanwhile, elephants have been destroying trees, predominantly *Acacia* and *Terminalia* species along the edge of the wetland, forming a transitional zone between the vlei and the protected forest area. The elephant density is estimated at 0.01/km<sup>2</sup> in the whole Sikumi forest and 0.52/km<sup>2</sup> in the wetland area. This has affected vegetation density as exhibited by broken trees in the areas adjacent to watering points.

### **3.4. Soil erosion linked to tourist activities**

Normally, tourists walk closer to wild animals at watering points to take pictures or films. The habituated elephants (by Allan Elliot since 1974) commonly found in the vlei area are not vicious to humans. Given the fact that each of the lodges receives more than 200 visitors per fortnight during the dry season, some walking paths often used by tourists to get closer to the watering points are gradually developing into rills and gullies and there is evidence of deposition in the vlei as shown in **Figure 8**. Gully development seems to be further influenced by fairly steep gradient, which on average is 4% (**Table 3**). Point D with the steepest slope has a more pronounced gully.

Moreover, two weirs were excavated in the lower section of the wetland in the late 1980s to impound more water for photographic safari activities. Coincidentally, weir construction and boreholes drilling started at the same time when additional lodges were established. However, there is evidence of soil erosion on some of the weirs. Erosion is as a result of overtopping of the weirs during the rainy, especially during the years when high rainfall was received in the area. The eroded sediments are likely to increase sediment yield downstream, which may be severe if high rainfall persists, since rainfall in the area is highly variable (**Figure 8**).

There is a gravel road constructed along the vlei to facilitate easy game drive by tourists around the wetland area. The gravel road has drains which control and discharge runoff into the vlei at certain points. Channelized flow is discharged into the wetland resulting in gully erosion, especially where vehicles use unplanned drive ways to cross the vlei during the dry season. Unplanned drive ways in the vlei result in vegetation loss and defined channels

**Figure 8.** Gully development along tourists' foot paths.

**Figure 7.** Section of the vlei altered by wildlife during salt licking.

178 Wetlands Management - Assessing Risk and Sustainable Solutions

species.

water from these sources.

national game park.

and 0.52/km<sup>2</sup>

the mid- to late 1990s in order to control the introduced Presidential Elephants, protected under a presidential decree of 1990 but instead the licks are attracting different wildlife

During the dry season when there is water shortage in the area, safari operators pump ground water from the wetland into open waterholes. These artificial watering points replenished by boreholes were established in the late-1980s across the lower section of the wetland, in proximity to lodges (**Figure 3**), to attract more wildlife for game viewing. Trampling is evident within 15 m around watering points as a result of large number of wild herbivores that drink

Due to high movement and frequency of wild animals in the vlei, mainly for water and salt licking, a number of wildlife trails or paths have been formed. Wild animals' trails are possibly facilitating the formation of several rills across the wetland area, especially in the lower section. The wildlife paths facilitate concentrated water flow, hence promoting soil erosion and siltation or sediment delivery into the wetland. Pressure on grazing by wild herbivores is a common phenomenon mainly around salt licks and watering points. Key informant interviewees attributed the grazing pressure to high wildlife populations and the presence of grazers around water points. This is more pronounced during the dry season due to physical water scarcity in the natural pans dotted around the forest area and in the adjacent Hwange

Meanwhile, elephants have been destroying trees, predominantly *Acacia* and *Terminalia* species along the edge of the wetland, forming a transitional zone between the vlei and the pro-

Normally, tourists walk closer to wild animals at watering points to take pictures or films. The habituated elephants (by Allan Elliot since 1974) commonly found in the vlei area are

in the wetland area. This has affected vegetation density as exhibited by broken

in the whole Sikumi forest

tected forest area. The elephant density is estimated at 0.01/km<sup>2</sup>

trees in the areas adjacent to watering points.

**3.4. Soil erosion linked to tourist activities**


**Table 3.** Slope gradient at selected interval along the vlei, in percentages.

for concentrated flow, a condition that enhances geomorphic process such as water erosion linked to surface runoff. The most pronounced developing gully is on average 3 m wide, 24 cm deep and 45 m long.

per season has been declining over the past four decades as shown by linear regression results (y = −2.932x + 672.8; r2 = 0.033), the occasional high rainfall occurrences noted in this study could also be attributed to excessive erosion activities. Arid conditions worsened by increasing minimum and maximum temperature also may expose the bare areas around salt licks to wind erosion. Therefore, the wetland is susceptible to both water and wind erosion given the changing climate in the area. Wind speed in the vlei may be high since the depression is predominantly

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Wildlife grazing is also influencing the alteration of the wetland's landscape. High grazing intensities by plain game species were mostly observed around watering points and were almost devoid of vegetation. The pressure on grazing has the potential to enhance soil erosion by exposing the soil facilitating surface runoff. Some previous studies revealed that the effect of cattle grazing around watering points is low [15] whereas that of wildlife was found to be high, characterised by absence of vegetation [10, 16, 17]. This explains why large-scale commercial farmers which occupied vleis in the early days limited the use of the vlei to late dry season grazing to avoid heavy grazing which resulted in erosion throughout the year [2]. In the case of the lower section of Dete vlei, pressure of wild grazing is high since grazing is continuous during the dry season while wild animals are attracted by watering points and salt licks to a central point. Therefore, strategies should be considered to regulate grazing around watering points and salt licks in order to mitigate soil erosion considering that bare conditions were not a common phenomenon in the upper section of the vlei which has no

Wildlife trampling which is well pronounced within a 15 m radius of watering points also results in top soil loosening and loss of vegetation cover, making the soil susceptible to erosion and possibly siltation of the existing water points. This finding concurs with [10] who acknowledged that the visibility of wild herbivores trampling around watering points results in vegetation cover reduction. According to [13], the continuous trampling by wild animals in a forage land accelerates the reduction of vegetation cover and ultimately exposes the soil

Wildlife vegetation destruction, especially *Acacia* trees by elephants, exposes soil to water erosion along the wetland fringes, facilitating increased sediment input into the wetland given its fairly steep gradient (**Table 2**). The effect of high elephant densities on vegetation and the environment in general is well documented [26]. This was complemented by findings by [27] that high elephant population results in severe environmental damage, loss of biodiversity and increased competition for scarce resources. In the case of Dete vlei, the elephant

area). According to the Ecologist and Forester, the current elephant population is beyond the optimum carrying capacity of the area. Considering that there are various wildlife species frequenting the vlei as well as a result of the presence of water during the dry season (**Figure 4**), the ecological carrying capacity of the vlei could have been severely exceeded as different wild animals compete for grazing; hence vegetation loss and the potential of soil erosion

in the whole of Sikumi forest (and 0.52/km<sup>2</sup>

in the wetland

grassland surrounded by forests, which could make it a trough for wind passage.

watering points and salt licks.

density is estimated at 0.01/km<sup>2</sup>

being accelerated in the vicinity of watering holes.

to erosion agents.

There are also unplanned roads that are used for game drive by tourists into the forest area surrounding the vlei. Some of the roads are developed following fairly steep gradients (on average 6% slopes) on the margins of forest area that forms the catchment area of the vlei into the wetland. Despite the fact that the predominant soil type is Kalahari sand (with high infiltration capacity), there is evidence of soil erosion on these roads as runoff is enhanced by the steep slope and channelized flow. Some of the sediment ultimately gets into the vlei, a situation likely to alter the ecological characteristics of the wetland due to enhanced sediment delivery.
