Where Bushveld meets Highveld grassland
Bronkhorstspruit, Gauteng, South Africa
Key words: grassland, dragonflies, damselflies, bushveld, vegetation, biome, South Africa, Highveld, Grootspruit, Wilge River, habitat, biotope
An undulating diverse landscape in one of the few protected areas within the Rand Highveld Grassland and Loskop Mountain Bushveld, frost tolerant grasslands drained by red-green wetlands of Imperata cylindrica and Limosella maior, contained within the embrace of rocky wooded ridges. The Ezemvelo Reserve offers access to the Wilgerivier and, its tributary the Grootspruit. The aquatic and riparian habitat diversity is impressive, with cobbled flowing waters, sandy deposits among the clay dominated grass-carpeted banks as well as densely vegetated pools utilized by game and fed by rocky seeps and steep grasslands.
Introduction
The Rand Highveld Grassland vegetation area is threatened due to various anthropogenic activities, nevertheless it still shows a kaleidoscope of species with floristic similarities to a wide range of vegetation types including savanna, kalahari and afromontane vegetation groups.
The variety of habitats, due to the vacillating landscape, provide a diversity of niches where aquatic, riparian and wetland areas form a multitude of ecotones, resulting in great diversity in a small spatial area. This all lends towards creating ideal habitat for the incredible variety of dragon- and damselflies. Sandy river banks deposited in sheltered river bends, dense vegetation in shallow clear wetland-rock pools provide ideal habitat for Odonata larvae.
Odonata
The aquatic habitats in the Ezemvelo Nature Reserve are highly variable which favours a rich Odonate fauna. The flowing waters with submerged cobble stones in a large open watercourse, the Wilge River, contains several niche habitats. Smaller river systems which drain at a steeper gradient allow for further diversified aquatic habitats. The pristine channeled valley bottom and seep wetlands serve to further increase the diversity of freshwater habitats.
Species seen in the Wilge and Grootspruit Rivers
The species pictured below, were recorded in the Wilge River and Grootspruit instream and marginal habitats.
Species seen in the Wetland Areas
These species were observed in the wetland areas, favoring the pools created in the grasslands draining into the larger Wilge River and Grootspruit.
Vegetation
Instream Species
Fully aquatic species of Najas graminea, clearly indicate the slow-and-constant flowing nature of the wetlands draining into the Grootspruit. The productive wetland pools also host Ludwigia palustris in vivid red contrast to the bright green surrounds. These pools are utilized extensively by game, likely aiding in the creation and maintenance of these deep areas in the otherwise sub-surface streams. These seeps form from the drainage of the surrounding grass- and woodland catchment area. It was surprising to note Enteromius bifrenatus in these apparently isolated pools.
These species are often found in saturated conditions but tolerate a fluctuating water table. Gomphostigma virtgatum with snow-drop flowers and grey-green rosemary-like foliage, can withstand flooding and is found adjacent to and inside of river channels; usually wedged into rocky crevices in the boulder-strewn riverbed and immediate floodplain. Limosella maior is found growing at the edges of the sensitive grassland wetland pools. Berula repanda can tolerate deeper constantly saturated conditions well; the toothed pinnate leaves and hollow stems provide distinctive features.
Utricularia sp. like rare drops of sunlight in the placid wetland pools, their bladders trap zooplankton to make-up for Nitrogen and Phosphorus deficiencies. Some South African healers and medicinal plant traders require rituals before the plant may be removed, as it is used to treat a variety of ailments. Not commonly seen due to wetlands often being overgrazed, as the thirsty cattle readily trample the delicate plants and increase erosion and subsequently sedimentation smothering them.
The following species were thriving in the wetland pools: Hydrocotyle bonariensis water loving and widespread. Shagnum sp. or peat moss, slowly decay as sediment is gradually washed over the shoots, slightly acidic conditions prevent rapid decay and these ever-growing buried shoots can, in the right conditions, form peat. Additionally they are considered to be indicators of good habitat and water quality conditions. Persicaria sp. arranged with minute pink bells dropping from cascading stems. Though it is always associated with water, Persicaria is hardy in any pond, pool, tank, saturated soils and even vase.
Wetland grasslands
Dierama medium. Lilac to deep purple bell-shaped flowers barely suspended from gently swaying panicles. Its tufted grass-like leafy base prefers rooting in wetlands, at home amongst the large Miscanthus junceus, both species providing critical stabilization of the steep slopes.
The angled wetlands remain well-vegetated year round even when the grasses turn to their pale gold-and-red shades. Imperata cylindrica and Miscanthus junceus form dense and expansive swathes carpeting the seeps and floodplains respectively. Cymbopogon sp. and Andropogon huillenisis grow in scattered tufts throughout the area.
Dinekia capensis. Surrounded by a vivid assortment of dragonflies, this white to purple flowering species is found at river edges and grassland wetlands between the ridges.
Rocky Ridges
Gerbera jamesonii. Nestled in the rocky scattered boulders of the ridges bordering the rivers and wetlands, the flame-bright Barberton daisy dazzles the eye. A small wonder it is commonly grown and bred for gardens worldwide.
Euphorbia cooperi. With the poisonous latex, known to be used to repel insects and birds, safely hidden behind a shiny and spiny green and red exterior, a host of insects enjoy the late winter offerings of the Euphorbia sp.
Occurring in scattered arrangements along even the steepest rocky cliffs, its candelabra-like and undulating form is distinctive, as are the globulous pale yellow flowers.
Crossandra greenstockii. found in the northern provinces of South Africa, a pyrophytic or fire tolerant species able to survive in the sometimes too-often burned pasturelands of South Africa.
References
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