Plant census and floristic analysis of selected serpentine outcrops of the Barberton Greenstone Belt, Mpumalanga, South Africa

Abstract

a b s t r a c tThis paper aims to characterise and describe the species composition of serpentine sites of the Barberton Greenstone Belt as compared to surrounding non-serpentine areas. A floristic analysis of seven serpentine (serpentinite) outcrops of the Barberton Greenstone Belt, in the eastern part of South Africa, recorded 744 species and subspecies, 319 genera and 94 families. 18 taxa remain undescribed. The Barberton Greenstone Belt flora includes 32 taxa endemic to serpentine soils and six taxa considered to be hyperaccumulators of nickel. The taxa considered to be endemic to serpentine outcrops make up 39% of the number of endemics found within the Barberton Centre of Endemism. The serpentine vegetation is characterised by fewer trees than the surrounding vegetation and the dominance of grass species such as Themeda triandra, Heteropogon contortus and Loudetia simplex. The species composition of each outcrop is relatively unique with only about 30% of species shared between any pair of outcrops. The flora of the serpentine outcrops of the Barberton Greenstone Belt is found to be different to the surrounding non-serpentine vegetation in terms of number of species per family, the ratios of dicotyledons to monocotyledons and familial composition.

Biological crusts of serpentine and non‐serpentine soils from the Barberton Greenstone Belt of South Africa

“…Serpentine outcrops in the Barberton Greenstone Belt occur in mountainous areas and are heterogeneous in altitude, slope, soil depth and other topographic features (Williamson and Balkwill 2015). Soil was sampled in February 2016 at different sampling localities along the Barberton Greenstone Belt in Mpumalanga, South Africa ( Fig.…”

“…Mean annual temperatures of the study area vary between 16.7 and 20.9°C and mean annual summer rainfall ranges from 518 to 1194 mm (Mucina and Rutherford 2006). The Drakensberg Escarpment divides Mpumalanga province into a westerly half consisting mainly of high-altitude grassland called the Highveld and an eastern half situated in low altitude subtropical Lowveld, mostly savanna habitat (Williamson and Balkwill 2015). Sites 1, 2, and 11-16 were sampled along the escarpment and are situated in a cool (mean annual temperature of 17°C) mist belt with a high frequency of fog and precipitation levels (> 1000 mm per annum), compared to sites 3-10 which are in subtropical Lowveld (19.7°C; < 800 mm).…”

Environmental Factors Influencing Tree Species Regeneration in Different Forest Stands Growing on a Limestone Hill in Phrae Province, Northern Thailand

“…The distribution of vegetation patterns is generally controlled by physical factors, such as light and soil conditions (McLaren and McDonald 2003;Guarino and Scariot 2012). Rocky outcrops, also referred to as edaphic islands (Williamson and Balkwill 2015), support species with physiological requirements that differ from those of species living in the surrounding landscape (Speziale and Ezcurra 2012).…”

“…These islands and their unique environment provide habitat for specialist plant species (Csergo et al 2014;Gao et al 2015). Rocky outcrops are often referred to as edaphic islands due to their sharp boundaries and patchy distribution (Williamson and Balkwill 2015). Vegetation cover on thin soils overlying limestone is extremely vulnerable to soil degradation, water loss, and erosion Thomas et al 2016).…”

A new species of Ochna (Ochnaceae) from the Barberton Mountains of Mpumalanga, South Africa

“…In 2013 and 2017, additional collections were made from the neighbouring reserve, Barberton Nature Reserve phase 3, a newly designated World Heritage Site recognised for the presence of the Barberton Greenstone Belt geological formation (Oosthuizen 2017). The Greenstone Belt boasts numerous serpentine outcrops that give rise to serpentine-derived soils, low in calcium and nutrient content, with high concentrations of nickel and chromium and poor water holding capacity (Harrison et al 2006, Williamson & Balkwill 2015. The harsh soil environment created by these physical and chemical properties only allow for serpentine-tolerant species to colonise, which in turn may lead to ecological speciation resulting in plant species restricted to these sites (Kruckeberg 1986, Rajakaruna 2004, Williamson 2016.…”