The Physical Environment and Major Plant Communities of the Heilbron-Lindley-Warden-Villiers Area, Northern Orange Free State

S.AfrJ.Bot., 1993,59(4): 345 - 359 345 The physical environment and major plant communities of the Heilbron-Lindley-Warden-Villiers area, northern Orange Free State E.R. Fuls, G.J. Bredenkamp, N. van Rooyen and G.K. Theron Department of Botany, University of Pretoria, Pretoria, 0002 Republic of South Africa Received 28 December 1992; revised 10 March 1993 An analysis of the physical environment and associated major plant communities of the Heilbron-Lindley Warden-Villiers area (northern Orange Free State) is presented. Releves were compiled in 263 stratified random sample plots. Care was taken to avoid severely degraded areas. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed three distinct vegetation types. These vegetation types were sub divided into seven major plant communities. A hierarchical classification, description and ecological inter pretation of the seven major plant communities are presented. The easily distinguishable major plant communities should be managed as separate ecological units in order to achieve optimal utilization and conservation of the vegetation of this part of the Grassland Biome. 'n Analise van die fisiese omgewing en geassosieerde hoofplantgemeenskappe van die Heilbron-Lindley Warden-Villiers gebied (noordelike Oranje-Vrystaat) word aangebied. Releves is in 263 gestratifiseerde, ewekansig gekose monsterpersele saamgestel. Daar is deurgaans gepoog om erg versteurde gebiede te vermy. 'n TWINSPAN-klassifikasie, verfyn deur Braun-Blanquet-prosedures, toon drie duidelik onderskeibare plantegroeitipes. Hierdie plantegroeitipes is onderverdeel in sewe hoofplantgemeenskappe. 'n Hierargiese klassifikasie, beskrywing en ekologiese interpretasie van hierdie sewe hoofplantgemeenskappe word gegee. Die maklik uitkenbare hoofplantgemeenskappe moet bestuur word as afsonderlike ekologiese eenhede om optimale benutting en bewaring van die plantegroei van hierdie deel van die Grasveldbioom te verseker. Keywords: Braun-Blanquet classification , ecological units, Grassland Biome, southern Africa, synecology. Introduction 28°S latitude (Figure 1), covering approximately one The world-wide retrogression of natural resources can million hectares. Larger towns situated in, or bordering on, primarily be ascribed to a 'cleverer-than-nature' approach the study area are Heilbron, Lindley, Reitz, Warden, Frank towards land-use and resource management (Jackson & fort and Villiers. The study area forms part of the Highveld Piper 1989). To manage natural resources in step with inland plateau and consists predominantly of smoothly nature, it is essential to conduct both extensive and intensive planed or gently rolling land surfaces of the miocene age baseline environmental surveys in all areas. Vegetation (Mentis & Huntley 1982). The area is situated between 1500 classification and mapping are prerequisites for ecologically and 1800 m above sea-level. Acocks (1988) recognized two and economically sound land-use planning, resource man veld types within the study area, Themeda Veld to Cymbo agement, optimal and sustainable resource utilization and pogon - Themeda Veld transition (Veld Type 53) in the conservation (Edwards 1972). Grazing areas in particular north and Cymbopogon - Themeda Veld (Veld Type 48) in need to be subdivided into ecologically homogeneous the south. grazing units to ensure optimal and sustainable utilization of forage resources (Tainton 1984; Danckwerts & Teague Physical environment 1989). Identification of ecologically sensitive areas, rare and Climate endangered plant communities and species, protection of Rainfall is erratic, consisting mainly of thunder-showers biodiversity and evaluations of the conservation status of an which are restricted to the warm summer months. The area all depend on baseline vegetation and habitat surveys. winter months are arid and cold with frost occurring both In order to provide a main classificatory reference frame frequently and extensively (Weather Bureau 1986). General work of plant communities and their associated habitats ly speaking, the long-term average annual rainfall within the within the western Grassland Biome, a detailed vegetation study area varies between 600 and 700 mm per year. There classification and mapping of the area has been undertaken is a discernible increase in rainfall from the north-west/north (see also Kooij 1990; Eckhardt et al. 1993; Fuls et al. 1992). to the south-east/south. This is illustrated by the average This study forms an integral part of the long-term goal to annual rainfall recorded (1984 - 1991) for the following compile a detailed syntaxonomic synthesis of the Grassland localities within the study area (Figure 1) (Weather Bureau Biome of southern Africa (Scheepers 1986). 1992a): Villiers 607 mm, Frankfort 636 mm, Reitz 653 mm, Lindley 703 mm and Warden 708 mm. In addition, the Study area southern and south-eastern parts are slightly cooler. The The study area lies within the climatic climax Grassland average annual temperature (1988 - 1991) recorded for Biome of southern Africa (Mentis & Huntley 1982) and is Frankfort is 15.3°e and for Warden 14.3°e (Weather situated between 27°45' and 29~ longitude and 27° and Bureau 1992b). 346 S.-Afr.Tydskr.Plantk.• 1993.59(4) 27'S LEGEND Sandstone!Mudstone! Shale of the Molteno ~ Formation Mudstone!Sandstone of the Tarkastad Formation ~ of the Beaufort Group Mudstone!Sandstone of the Adelaide Formation E3 of the Beaufort Group Shale of the Volksrust °0:=:0 Formation of the Ecca 0 Group 27'30'S Sandstone!Shale of the §i Vryheid Formation of the Ecca Group Doletrite (Dykes and Sills not mapped) Area completed 1991 0 (see Fuls et al. 1992) o 10 20km ! Figure 1 Geology of the study area [adapted from Department of Mineral and Energy Affairs data (1984)]. Geology can be divided into a northern part and southern part. In the The study area lies within the main Karoo Basin (SACS northern areas the terrain is mostly mildly undulating to flat 1980). The area is primarily underlain by the Ecca and with a few distinct hills and ridges. Schematic illustrations Beaufort groups of the Karoo Sequence (Figure 1). The of the generalized terrain morphology encountered in the Ecca Group consists essentially of shale with sandstone northern areas are presented in Figures 3A and 3B. The featuring permanently only at the margin of the basin southern areas often have a more distinct undulating terrain (SACS 1980). The Beaufort Group consists primarily of morphology, frequented by low to medium-high hills and mudstone with cross-bedded sandstone occurring frequently. ridges. The generalized terrain morphology of the southern Argillaceous rocks are generally laminated and platy areas is summarized in Figures 4A and 4B. weathering in the Ecca Group and blocky-weathering in the Soil type apparently has a lesser influence on the vege Beaufort Group (SACS 1980). Between Heilbron and Frank tation distribution than soil depth, soil moisture and rocki fort massive dolerite intrusions are found (Figure 1). Hills ness. Plant communities could not be related exclusively to and ridges in the study area are predominantly associated specific soil forms. The soil forms which were encountered with dolerite dykes and sills which occur throughout the in the different terrain units are given in Figures 3 and 4. area. The dominant soil forms recorded were Glenrosa, Mayo, Avalon, Bonheim, Tukulu, Sepane and Rensburg (Depart Land types ment of Agricultural Development 1991). Land types are distinguished from each other in terms of one, or a combination, of the following parameters: terrain Drainage morphology, soil pattern/types and climate (Land Type Sur The entire study area lies within the catchment area of the vey Staff 1984). Five different land types are encountered in Vaal Dam (Figure 5). The drainage, water availability and the study area (Figure 2). water utilization within this area is therefore of great It was found that the vegetation of the study area is not importance to the densely populated Pretoria-Witwaters discernibly related to land types per se, therefore the land rand-Vereniging area, which relies heavily on the water types will not be discussed individually. The phytosociology resources of the Vaal Dam. Major rivers associated with the of the vegetation of the study area is primarily influenced by study area include the Vaal River, Wilge River, Klip River, soil moisture variations on a macro- and micro-scale, utili Liebenbergsvlei River and Cornelis River (Figure 5). Most zation by herbivores and terrain morphology. rivers .and streams within the study area end up as tributaries to the Wilge River which, together with the Vaal River, con Terrain morphology and soils tributes most of the water to the Vaal Dam water resources. According to terrain morphology variations, the study area The overall drainage of the study area is variable with the S.AfrJ.Bot., 1993, 59(4) 347 Bd land type Bd land type Dc land type Ea land type Vaal Dam Area completed 1991 Isee Fuls et al. 1992) o 10 20km 28°S 28°E 28"30'E 29°E Figure 2 Land types of the study area [adapted from Department of Agriculture (1979)]. major portion thereof reasonably to well drained. Incision of application of Braun-Blanquet procedures (see also Breden smaller streams is mostly shallow owing to the flat to kamp et al. 1989; Kooij et al. 1990). A synoptic table was undulating terrain. For the same reason streamflow tends to compiled for the major plant communities from the fina l be rather slow. Only a few pans,

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