**4. Occurrence and distribution of** *V. karroo* **in South Africa**

A TWINSPAN classification of historical data comprising 1553 relevés and 2006 species, compiled from all areas of South Africa where *V. karroo* is known to occur, was conducted and produced five main vegetation types, namely savanna, grassland, riparian thickets, wetland and Nama-Karoo communities. The riparian thickets and Nama-Karoo communities will only be mentioned briefly in this section, because they form the core of the *Acacia* (*Vachellia*) *karroo* Class suggested and described in more detail by Dingaan [54].

## **4.1. Savanna communities**

other parts are used medicinally in many ways. An infusion of the bark is used to cure diarrhoea and dysentery, while the dried and powdered form of its gum is used for eye treatments [2]. A boiled liquid from the bark is sometimes used to treat cattle which have tulp poisoning caused by *Moraea* (*Homeria*) species, which are bulbous plants poisonous to cattle [6]. Other *Vachellia* species are known to have medicinal properties as well. For example, the bark of *V. erioloba* is used to treat headaches and that of *V. xanthophloea* is used for fevers and

In addition to all the domestic uses of *V. karroo*, various commercial products are also obtained from the tree, of which gum is one of the most important (**Figure 6**). In fact, *V. karroo* gets its common name "sweet thorn" from this gum which comes out from wounds in the bark [6]. It is a pleasant tasting gum that is eaten by people and animals and has also been used for confectionary and adhesives [2, 16]. This gum is similar to gum arabic, which is widely used

The wood of *V. karroo* is hard and tough, making it suitable for making furniture, poles, and fence-posts [2]. It is also used to make wooden carvings (ornaments), which are very popular ornaments in the tourism industry [1]. The bark is used to make strong ropes and mats [2]. This bark and that of several other *Vachellia* species, notably *V. nilotica* (bark and pods)

for thickening many convenience foods, pharmaceuticals and cosmetics [1].

**Figure 6.** *Vachellia karroo* tree exuding gum (photo: M. Dingaan).

eye complaints [1].

120 Pure and Applied Biogeography

**3.2. Commercial value**

Savannas are one of the main biomes in the world and are the dominant vegetation in Africa and southern Africa [55], especially in Botswana, Namibia and Zimbabwe [56]. In South Africa, the Savanna forms the largest biome and occupies over one-third (33.49%) the country's area [57]. It is well developed in Northern Cape, North-West, and Limpopo Provinces; it is also found in parts of Mpumalanga, KwaZulu-Natal, and Eastern Cape Provinces and has isolated occurrences in Gauteng and Free State Provinces. The factors delimiting the biome are complex and can be an interplay of altitude, climate, soils, herbivory, and fire [39, 56, 58]. The biome mostly occurs at altitude ranging from sea level to 2000 m; rainfall is seasonal with wet summers and dry winters and varies from 200 to 1000 mm per year (**Figure 7**) frost may occur from 0 to 120 days per year, with frost free days in lowlying areas and longest frost periods in high-altitude areas [56, 58]. Approximately 8.5% of the biome is conserved in South Africa [57], a fairly good proportion compared to the other biomes. There are several conservation areas in the biome, which include the Kruger National Park. Savanna areas have not been adversely impacted by urbanisation, which could have been hindered by the hot, moist climate and diseases such as malaria [56, 57].

The Savanna biome in South Africa is described by Low and Rebelo [56] and Scholes [55] as vegetation characterised by a grassy ground layer 0.5–2 m tall and a distinct upper layer of woody plants 2–10 m tall (**Figure 8**). It may be delineated according to the height and degree of canopy cover of the tree layer as follows: shrubland, woodland, or bushveld depending on whether the upper layer is near the ground, dense or in the intermediate stages, respectively [55, 56]. Savanna vegetation may be broadly divided into fine-leaved savannas found in nutrient-rich and arid environments and broad-leaved savannas in nutrient-poor and moister environments [55, 58]. Broad-leaved species such as *Terminalia sericea, Burkea africana,* various *Combretum* species*, Pterocarpus rotundifolius* and several others dominate the higher rainfall

**Figure 7.** Rainfall and temperature for selected locations in the three representative biomes of South Africa [54].

areas, while the more arid savanna is dominated by microphyllous species where numerous *Vachellia* (and *Senegalia*) species dominate the tree component, but *Colophospermum mopane* is the broad-leaved exception [55].

The areas of the Savanna biome where *V. karroo* occurs are mainly in the Limpopo and North-West Provinces (**Figure 9**), and vast communities of *V. karroo* also occur in the Kalahari region in the Northern Cape Province. It can also be found in parts of the Eastern Cape and Western Cape Provinces. *V. karroo* communities can be encountered on predominantly sandy soils on bottomlands, footslopes, and mountain slopes. They can also be found as riparian thicket on clayey soils along stream and riverbanks.

Communities that make up this vegetation type are listed in **Table 3**, with the two most prominent as follows: The first is the *Acacia karroo–Panicum maximum* Open Woodland [62] *Vachellia* (*Acacia*) *karroo* Communities in South Africa: An Overview http://dx.doi.org/10.5772/intechopen.70456 123

areas, while the more arid savanna is dominated by microphyllous species where numerous *Vachellia* (and *Senegalia*) species dominate the tree component, but *Colophospermum mopane* is

**Figure 7.** Rainfall and temperature for selected locations in the three representative biomes of South Africa [54].

The areas of the Savanna biome where *V. karroo* occurs are mainly in the Limpopo and North-West Provinces (**Figure 9**), and vast communities of *V. karroo* also occur in the Kalahari region in the Northern Cape Province. It can also be found in parts of the Eastern Cape and Western Cape Provinces. *V. karroo* communities can be encountered on predominantly sandy soils on bottomlands, footslopes, and mountain slopes. They can also be found as riparian thicket on

Communities that make up this vegetation type are listed in **Table 3**, with the two most prominent as follows: The first is the *Acacia karroo–Panicum maximum* Open Woodland [62]

the broad-leaved exception [55].

122 Pure and Applied Biogeography

clayey soils along stream and riverbanks.

**Figure 8.** Savanna near Kimberley (top) and at Mokala National Park (middle, bottom), Northern Cape, South Africa (photos: M. Dingaan).

**Figure 9.** Distribution of selected *Vachellia karroo* communities.

found mainly along the banks of Ngwaritzi and Olifants Rivers south of Polokwane in the Limpopo Province. The second is the *Panico maximi–Acacietea tortilis* Class, described by Winterbach et al. [59] as microphyllous thorny bushveld that is associated with dark, clayey soils in low-lying areas. Other communities in the savanna where *V. karroo* occurs include the *Kirkia wilmsii*–*Terminalia prunioides* Closed Mountain Bushveld described by Siebert et al. [61]. This vegetation occurs within the Sekhukhuneland Centre of Plant Endemism (SCPE), which stretches from the Limpopo Province into the Mpumalanga Province and includes towns such as Roossenekal, Steelpoort and Sekhukhune. The vegetation is predominantly restricted to the warm slopes and valleys of undulating hills and mountains.

#### **4.2. Grassland communities**

The South African Grassland biome is part of the global temperate grassland biome [69]. It is the third largest biome in the country and covers 25.71% of South Africa [57] The biome is


found mainly along the banks of Ngwaritzi and Olifants Rivers south of Polokwane in the Limpopo Province. The second is the *Panico maximi–Acacietea tortilis* Class, described by Winterbach et al. [59] as microphyllous thorny bushveld that is associated with dark, clayey soils in low-lying areas. Other communities in the savanna where *V. karroo* occurs include the *Kirkia wilmsii*–*Terminalia prunioides* Closed Mountain Bushveld described by Siebert et al. [61]. This vegetation occurs within the Sekhukhuneland Centre of Plant Endemism (SCPE), which stretches from the Limpopo Province into the Mpumalanga Province and includes towns such as Roossenekal, Steelpoort and Sekhukhune. The vegetation is predominantly restricted

The South African Grassland biome is part of the global temperate grassland biome [69]. It is the third largest biome in the country and covers 25.71% of South Africa [57] The biome is

to the warm slopes and valleys of undulating hills and mountains.

**Figure 9.** Distribution of selected *Vachellia karroo* communities.

**4.2. Grassland communities**

124 Pure and Applied Biogeography


**Table 3.** Classification and habitat features of savanna communities.

found mainly on the high central plateau (Highveld) comprising the Free State and Gauteng Provinces and is also found in parts of Mpumalanga Province and the inland areas of KwaZulu-Natal and Eastern Cape Provinces. Most of the large urban areas are concentrated in the biome, and consequently, the grassland biome has the greatest urban population density in South Africa [57]. The urban expansion, coupled with conversion of natural grassland to cultivated land, has resulted in a huge decline in biodiversity in this biome [70]. Most of the grassland is converted for the production of crops such as maize, wheat, sorghum and sunflower. Compared to the savanna, conservation of grasslands is relatively low with only 1.12% of the biome conserved [57].

The distribution of the biome is determined by an interplay of climate, topography, fire and grazing [71]. The overall extent of the biome is mainly determined by climate, especially the amount of summer rainfall and minimum winter temperatures [69]. The grass dominance is maintained by frosts, fire and grazing, which also prevent the establishment of trees [56]. However, the role of fire in maintaining grassland is greater in humid (>650 mm of annual rainfall) than semi-arid regions (<650 mm of annual rainfall) [69, 71]. The biome is limited to altitudes varying from near sea level to 2850 m above sea level; the winters are cold, dry with frequent occurrences of frost; rainfall varies spatially from 400 to 2500 mm per annum and occurs mainly during the summer season [57, 69]. The topography is mainly flat to slightly undulating and may include mountainous regions [69].

The biome comprises grasslands that are dominated by a single layer of grasses (**Figure 10**), with forbs forming an important but usually not dominant component. The dominant grasses in the biome are of the genera *Andropogon, Cymbopogon, Diheteropogon, Heteropogon, Hyparrhenia, Monocymbium, Schizachyrium, Themeda, Trachypogon* and *Tristachya* [69]. Trees are generally absent, except in a few localised habitats. The woody component is usually limited to higher

found mainly on the high central plateau (Highveld) comprising the Free State and Gauteng Provinces and is also found in parts of Mpumalanga Province and the inland areas of KwaZulu-Natal and Eastern Cape Provinces. Most of the large urban areas are concentrated in the biome, and consequently, the grassland biome has the greatest urban population density in South Africa [57]. The urban expansion, coupled with conversion of natural grassland to cultivated land, has resulted in a huge decline in biodiversity in this biome [70]. Most of the grassland is converted for the production of crops such as maize, wheat, sorghum and sunflower. Compared to the savanna, conservation of grasslands is relatively low with only

**Community Location and habitat Refs.**

Vicinity of Turfloop Dam, Limpopo

Found on slopes of the Magaliesberg Also on flat surfaces with clay-loam soils

Clayey soils

Orange River

**Table 3.** Classification and habitat features of savanna communities.

Reserve), North-West

Mainly occurs along streams and adjacent areas

Augrabies Falls National Park, Northern Cape

Dominant soil forms are Dundee and Oakleaf

Kgaswane Mountain Reserve (formerly Rustenburg Nature

Associated with drainage lines, floodplains and islands of the

Situated on the banks of the Moretele River and tributaries (BNR)

[65]

[64]

[67]

[68]

Loamy to clayey soils, sandy soils in some tributaries

The distribution of the biome is determined by an interplay of climate, topography, fire and grazing [71]. The overall extent of the biome is mainly determined by climate, especially the amount of summer rainfall and minimum winter temperatures [69]. The grass dominance is maintained by frosts, fire and grazing, which also prevent the establishment of trees [56]. However, the role of fire in maintaining grassland is greater in humid (>650 mm of annual rainfall) than semi-arid regions (<650 mm of annual rainfall) [69, 71]. The biome is limited to altitudes varying from near sea level to 2850 m above sea level; the winters are cold, dry with frequent occurrences of frost; rainfall varies spatially from 400 to 2500 mm per annum and occurs mainly during the summer season [57, 69]. The topography is mainly flat to slightly

1.12% of the biome conserved [57].

4.4.3. *Ziziphus mucronata–Acacia* 

126 Pure and Applied Biogeography

Note: Although this community is similar to the communities of the *Vachellia karroo* Class suggested by Dingaan [54] in that it is *Vachellia karroo*–dominated riparian vegetation, it shows more affinity towards communities of the *Panico maximi–Acacietea tortilis* and is hence correctly included by Winterbach

4.5. *Acacion hebecladae–rehmannianae*

5. *Eustachys mutica–Acacia caffra*

6. *Ziziphus mucronata* Closed

*karroo* Woodland

[64] in this class

Alliance

Woodlands

Woodland

undulating and may include mountainous regions [69].

**Figure 10.** Grasslands near Bloemfontein (top), Bethlehem (middle) and Winburg (bottom), Free State Province, South Africa (photos: M. Dingaan).

moisture areas such as hills, gullies, valley slopes and is also found on azonal alluvial soils. The woody species often found in grassland are *V. karroo, V. sieberiana,* species of *Protea, Cussonia, Diospyros, Gymnosporia* and many more. Some of these trees and shrubs can tolerate frequent fires by being serotinous and through their ability to resprout after fires [69]. The Grassland biome can be divided into two classes (sweet and sour grasslands), based on moisture availability and palatability to livestock. Sweet grasslands (locally known as sweetveld) are dry grasslands that occur on base-rich soils at lower altitudes and remain palatable and nutritious throughout the year. Sour grasslands (sourveld) are moist grasslands generally found on leached soils at higher altitudes, which are palatable only in spring and summer [69, 72].

*Vachellia karroo* occurs throughout the biome and often encroaches on degraded grasslands. It is found on plains where soils are sufficiently deep, as well as in sheltered sites on the slopes, where habitat conditions are relatively moist. Communities where it is found are listed in **Table 4** and the two most prominent are as follows: The first is the *Themeda* 



**Table 4.** Classification and habitat features of grassland communities.

*triandra–Eragrostis plana* Class proposed and described by Du Preez and Bredenkamp [76] as moist grasslands of the plains at relatively high altitudes and high rainfall. The second is the *Geigeria burkei–Melinis repens* community; the individual communities that represent this vegetation type were identified and described by De Frey [83], but they are classified together under one major community for the first time in the present classification. This is vegetation of the mountains and plains of southeastern Mpumalanga, specifically the area comprising the towns of Belfast, Barberton, Piet Retief, and Wakkerstroom. It is associated with sandy loam soils, with Glenrosa as the dominant soil form.

#### **4.3. Riparian thickets**

moisture areas such as hills, gullies, valley slopes and is also found on azonal alluvial soils. The woody species often found in grassland are *V. karroo, V. sieberiana,* species of *Protea, Cussonia, Diospyros, Gymnosporia* and many more. Some of these trees and shrubs can tolerate frequent fires by being serotinous and through their ability to resprout after fires [69]. The Grassland biome can be divided into two classes (sweet and sour grasslands), based on moisture availability and palatability to livestock. Sweet grasslands (locally known as sweetveld) are dry grasslands that occur on base-rich soils at lower altitudes and remain palatable and nutritious throughout the year. Sour grasslands (sourveld) are moist grasslands generally found on leached soils at higher altitudes, which are palatable only in spring and summer [69, 72]. *Vachellia karroo* occurs throughout the biome and often encroaches on degraded grasslands. It is found on plains where soils are sufficiently deep, as well as in sheltered sites on the slopes, where habitat conditions are relatively moist. Communities where it is found are listed in **Table 4** and the two most prominent are as follows: The first is the *Themeda* 

**Community Location and habitat Refs.**

Northern Mpumalanga

dolerite hills and ridges

the slopes of dolerite hills

Free State Province

Bloemfontein, Free State Province

rocky outcrops of the Beaufort Formation

High altitudes and high rainfall

North-western KwaZulu-Natal

Slopes and footslopes of rocky hills

Bergville and Winterton

Deep sandy soils

Diverse soil types and forms

Plains and slopes

Valley

outcrops

Belfast-Lydenburg-Dullstroom area

North-eastern Mpumalanga and south eastern Limpopo

(i) Shrub communities occurring along the Upper Orange River

(ii) Shrub communities typical of the talus slopes of mountains,

Relatively moist habitats found in gorges and drainage lines on

Willem Pretorius Nature Reserve, Winburg-Ventersburg area,

Shrubland occupying plateaus and steep slopes of dolerite hills,

Includes the towns Estcourt, Colenso and Ladysmith, as well as

Plains adjacent to the footslopes of the Drakensberg Soils mostly shallow, sandy or sandy loam

Also includes grassy shrubland communities on low dolerite

[73]

[74]

[75] [77]

[77]

[78]

[76]

[79]

[79]

Mountain sourveld on dry dolomitic regions Rock outcrops near or on the bottom of valleys Some protected areas on valley sides

1. *Acacio ataxacanthae–Celtidetum africanae*

2. *Acacia karroo–Gladiolus ecklonii–Themeda* 

Originally described by Werger [75] In present classification, it represents the shrub communities of southern and eastern Free State as described by Du Preez and

3.1. *Ehrharto–Oleetum–rhoetosum lanceae*

Part of the *Chrysocomo–Selagenea albidae*

Synonym: *Grewio–Isoglossion grantii* Alliance

Part of the *Rhoo–Rhoicissenea tridentatae* sub-

4.1. *Chaetacanthus costatus–Cymbopogon* 

Described by Robbeson [79] as Open Thornveld, a variation of Acocks' [27]

4.1.1. *Hermannia depressa–Anthospermum* 

4. *Themeda triandra–Eragrostis plana* Class Moist grasslands of the plains

3.2. *Rhoo–Scolopion* Alliance

class proposed by Du Preez [77]

*excavatus* Open Thornveld

Southern Tall Grassveld

*rigidum* Sub-community

*triandra* Open Woodland

128 Pure and Applied Biogeography

3. *Rhoetea erosae* Class

Bredenkamp [76]

Sub-association

sub-class [77]

Du Preez [77]

Association

The riparian thickets dominated by *V. karroo* are mainly associated with deep, clayey alluvial deposits that occur along stream and river banks (**Figure 11**) and occasionally on

**Figure 11.** Riparian vegetation along the Modder River near Glen (top, middle) and Sand River near Ventersburg (bottom), Free State Province, South Africa (photos: M. Dingaan).

the river beds. The thickets also extend to the floodplains and bottomlands adjacent to the watercourses and also on gradual footslopes of hills and ridges. This vegetation type forms the core of the *Acacia* (*Vachellia*) *karroo* Class suggested and described in more detail by Dingaan [54].
