Vachellia (Acacia) karroo Communities in South Africa: An Overview

Abstract

Vachellia karroo is a useful and widespread tree in Africa. It belongs to the family Fabaceae, which is the third largest woody plant family in southern Africa. This is an ecologically and economically important species as almost all of its parts, including bark, pods, seeds, leaves and thorns, are extremely useful to both humans and animals. Various commercial products are also obtained from the tree, and gum is one of the most important products. V. karroo in South Africa has an extensive distribution range that includes several biomes. It is very adaptable and has wide habitat tolerance, growing under many differing conditions of soil, climate, and altitude. Although it is often associated with heavy, clayey soils on the banks of rivers and streams, it also grows in bushveld, dry thornveld, grassland and woodland. V. karroo is easy to grow and as a result can become an aggressive invader of valuable farming land and grazing areas, a phenomenon usually referred to as bush encroachment. An analysis of historic data comprising 1553 relevés and 2006 species, compiled from all areas of South Africa where V. karroo is known to occur was conducted, and TWINSPAN classification produced five main vegetation types.

Both Alpha- and Beta-Rhizobia Occupy the Root Nodules of Vachellia karroo in South Africa

“…We also showed that a high diversity of rhizobial symbionts associate with V. karroo in the various regions, even in the Grassland biome where we identified putative species from three genera. The latter is important because V. karroo contributes significantly to bush encroachment (i.e., the change of grasslands to ecosystems containing more shrubs and trees), which is particularly evident in the Grassland biome in the Eastern Cape, North West and Free State provinces of South Africa (Dingaan and du Preez, 2018). The promiscuity of V. karroo in these and other settings therefore suggest that finding a suitable rhizobial partner is not a hurdle to the establishment or spread of this legume and likely represents an important driver or facilitator of its ecological success.…”

“…It has been shown to have medicinal properties as its leaves and bark can be used to treat diarrhoea, while an exudate from the tree can be used as an emollient for conjunctivitis and parts of the tree also have broad-spectrum anti-microbial activity (van Wyk, 2011; Cock and van Vuuren, 2015; Maroyi, 2017). The leaves, pods and fruits have the potential to be used as fodder for ruminant livestock (Gxasheka et al, 2015; Brown et al, 2016; Dingaan and du Preez, 2018), while its flowers are important for honey production (Dingaan and du Preez, 2018). With regards to human consumption, its roasted seeds can be used as a coffee substitute and its gum in the production of sweets (Cock and van Vuuren, 2015).…”

“…Among tree species, V. karroo has the widest distribution in South Africa (Dingaan and du Preez, 2018), extending from the Southwestern Cape northwards into Namibia, Botswana, Zambia, Angola and Zimbabwe (Taylor and Barker, 2012). The species can grow in different soils (ranging from sand to heavy clays), in relatively wet to arid areas (200–1500 mm annual rainfall) and from sea level to an elevation of 1800 m (Maroyi, 2017).…”

“…As a pioneer, V. karroo inhabits various biomes and has the ability to grow and thrive in a range of climatic and edaphic conditions (Brain et al, 1997; Taylor and Barker, 2012), where it is resistant to factors such as salinity, drought, fire and frost (Brain et al, 1997). This is thought to contribute significantly to its invasiveness, because V. karroo is the foremost woody invader in South African grasslands (O’Connor, 1995; Taylor and Barker, 2012), a phenomenon referred to as “bush encroachment” (Dingaan and du Preez, 2018).…”

Rhizosphere Diazotrophs and Other Bacteria Associated with Native and Encroaching Legumes in the Succulent Karoo Biome in South Africa

“…The consequences of such invasions include loss of native plant diversity and changes in the structure and composition of microbes in the soil [20,24]. This could also be the case for the noted encroachment of Vachellia karroo in the SKB from other biomes in South Africa [17,25], which is a topic that has not been addressed previously.…”