Combretum Hereroense–Grewia Vernicosa Open Mountain Bushveld

Vegetation ecology of Sekhukhuneland, South Africa: Combretum hereroense–Grewia vernicosa Open Mountain Bushveld

SJ Siebert1,2*, AE van Wyk1 and GJ Bredenkamp1

1 Department of Botany, University of Pretoria, Pretoria 0002, South Africa 2 Present address: SABONET, c/o National Botanical Institute, Private Bag X101, Pretoria 0001, South Africa * Corresponding author, e-mail: [email protected]

Received 18 September 2001, accepted in revised form 30 August 2002

A hierarchical classification, description, and ecological sub-associations. Many new syntaxa are described and and floristic interpretations are presented on one of the ecologically interpreted. For each of the plant commu- six major vegetation types of the Sekhukhuneland nities the species richness, endemism and conserva- Centre of Plant Endemism, namely the Combretum tion status were determined. A selected set of environ- hereroense–Grewia vernicosa Open Mountain mental factors is provided to aid with the delimitation of Bushveld. Relevés were compiled in 91 stratified ran- plant communities. The floristic information, proposed dom plots. A TWINSPAN classification, refined by classification, general description and vegetation key Braun-Blanquet procedures, revealed 20 plant commu- can be used for future identification of conservation nities, which are divided into six associations and 19 areas, land-use planning and further research.

Introduction

Although phytosociological studies have been conducted on Siebert et al. (2002) recorded six major vegetation types the savannas of ultramafic substrates in southern Africa for the SCPE during a comprehensive vegetation and floris- (Werger et al. 1978, Van der Meulen 1979), several vegeta- tic survey of the savannas and grasslands of the 4 000km2 tion types associated with this type of substrate remain poor- of ultramafic rock of the eastern Rustenburg Layered Suite. ly investigated and documented. An example of ultramafic This was probably the most extensive survey of vegetation vegetation which has never been studied in detail, is the in a single ultramafic region since the comprehensive sur- Mountain Bushveld identified by Siebert et al. (2002) on the veys conducted by Jaffré (1980) on the serpentine flora of norite, pyroxenite and anorthosite hills and mountains of the New Caledonia. It is envisaged that the identification, classi- Sekhukhuneland Centre of Plant Endemism [SCPE] (Van fication and description of the various vegetation units will Wyk and Van Wyk 1997, Van Wyk and Smith 2001). contribute to the knowledge of the ecological and floristic Ultramafic mountains and hills are floristically noteworthy in intricacies of the SCPE’s Mountain Bushveld and ultramafic that they usually harbour many endemic plant species that are regions in general. restricted to, and communities that are associated with, this This paper characterises and interprets the vegetation particular geological substrate (Brooks and Malaisse 1985, units and the associated habitats of the Open Mountain Iturralde 1995, Madulid and Agoo 1995, Siebert et al. 2001). Bushveld [OMB] of the Sekhukhuneland Centre (Siebert et Various savanna vegetation types have been recognised al. 2002). An assessment of the plant diversity, endemism in areas adjacent to the SCPE, on the dry dolomitic hills and and threatened taxa of the various plant communities of the mountains of the northeastern Drakensberg Escarpment OMB is supplied to aid future conservation actions in the (Matthews et al. 1992), the western Rustenburg Layered region. A vegetation key is presented to assist with the easy Suite (Coetzee 1975) and the northeastern plains of the identification of the syntaxa of the OMB in the region. Habitat Springbok Flats (Breebaart and Deutschlander 1997). The data are provided to aid with future, more comprehensive SCPE shares many near-endemics and shows a definite ecological interpretations. floristic affinity (Siebert 1998) with these areas. Acocks At a local level the data provided with this study are basic (1988) mapped the savanna in the SCPE as three major to the formulation of management policies, as phytosociolo- veld types, namely Mixed Bushveld, Sourish Mixed gy has a regular application in ecosystem management, for Bushveld and North-Eastern Sandy Highveld Grassland. A an adequate database of natural features, such as the vege- more generalised classification of the same region’s vegeta- tation and physical environment, is essential for effective tion is given by Low and Rebelo (1996), which recognises land-use management and implementation (Kent and Ballard only one major vegetation type, namely Mixed Bushveld. 1988, Bedward et al. 1992, Rhoads and Thompson 1992). 476 Siebert, Van Wyk and Bredenkamp

Study Area value assigned to each according to the Braun-Blanquet scale (Mueller-Dombois and Ellenberg 1974), namely R = The study area comprises the central part of the SCPE rare, + = <1%, 1 = <5%, A = 5–12%, B = 12–25% and 3 = (Figure 1), between 24°40’ and 25°20’S latitude; 29°50’ and 25–50% cover. 30°30’E longitude. The whole SCPE is defined and dis- Phenological changes over the sampling period influ- cussed in Siebert et al. (2002), where it is emphasised that enced the species cover and consequently the data of the the SCPE is more or less restricted to the Rustenburg relevés (Fischer 2000). Plant species names follow Retief Layered Suite, one of the stratigraphic units of the Bushveld and Herman (1997) and general practice followed at the Complex. The extent of occurrence of the Mountain HGWJ Schweickerdt Herbarium (PRU), University of Bushveld is approximately 2 500km2 and is characterised Pretoria. Terminology to describe vegetation structure is by considerable diversity in geology (Kent 1980) and phys- based on Edwards (1983). Environmental data recorded in iography (Land Type Survey Staff 1989). each sample plot include terrain type (Land Type Survey The average annual rainfall for the Mountain Bushveld Staff 1987, 1988, 1989), aspect, slope, geology (Visser et al. region is 550mm (South African Weather Bureau 1998), but 1989), soil type (MacVicar et al. 1991) and rockiness of soil the rainfall pattern is strongly influenced by the local topog- surface. Longitude and latitude readings were recorded for raphy (Siebert 1998). Rainfall varies from as little as 400mm each sample plot using a Global Positioning System. All in some of the valleys, to an estimated 600mm on the east- relevé data are stored in the TURBOVEG database ern slopes of mountains (Erasmus 1985). Temperatures for (Hennekens 1996a) and located at the Department of the Mountain Bushveld region range from 0°C to 38°C, with Botany, University of Pretoria (Mucina et al. 2000). a mean daily temperature of 20°C (South African Weather A first approximation of the vegetation classification, based Bureau 1998). Temperatures vary at different localities with- on a total floristic data set of 415 relevés for the SCPE, was in the area, also correlating strongly with physiographic fea- obtained by the application of Two-Way Indicator Species tures, being higher in the low-lying valleys and lower on the Analysis (TWINSPAN) (Hill 1979). This first step of an objec- high-lying plateaus (Buckle 1996). The northern and western tive multivariate classification identified several major vege- parts of the study area are on average warmer and drier tation types. The result was then used to subdivide the data than the southern and eastern parts (Siebert 1998). set into six phytosociological tables, each representing one of Soils of the study area are typical for ultramafic areas the major vegetation types of the SCPE (Siebert et al. 2002). (Siebert et al. 2001), as certain areas exhibit Mg/Ca ratios One of these, consisting of 91 relevés, was again subjected (>1) similar to that of serpentine, they are rich in chromium, to standard TWINSPAN cut levels and the subsequent divi- cobalt, iron, nickel, and deficient in the nutrients calcium, sions were adopted as homogeneous groups of relevés rep- molybdenum, nitrogen, phosphorous and potassium resenting plant communities of the OMB. (Johnston and Proctor 1981, Brooks 1987). However, a low Using Braun-Blanquet procedures in the MEGATAB com- Mg/Ca ratio (<1) has also been recorded along lower moun- puter programme (Hennekens 1996b), the species groups tains slopes of certain areas in the SCPE (Siebert 1998), a were further refined. The partial subjectivity of this process phenomenon presumably caused by a reduction in the bind- is controversial in that it is not fully formalised, but serves to ing strength of Mg due to topsoil acidification and subsequent find coincidence patterns which carry ecological information. Mg leaching (Roberts and Rodenkirchen 1995). Soils of the Species groups were only recognised if the species was rep- study area have a moderate pH (6–8) (Loock et al. 1982). resented in a group of relevés more often than outside the The Mountain Bushveld of the SCPE can broadly be group and if the resultant group could be ecologically inter- described as savanna of undulating norite and pyroxenite preted. All syntaxa were hierarchically classified according hills and mountains, which is bordered by a northeastern to Westhoff and Van der Maarel (1978) and formally named Sandy Highveld Grassland-Mountain Bushveld ecotone in according to Weber et al. (2000). the south and a Mountain Bushveld-Mixed Bushveld eco- Alpha diversities of the different plant communities were tone in the north (Acocks 1988, Siebert et al. 2002). Due to calculated to identify areas of high plant species richness. the heterogeneity of the environmental factors in the study Plant species richness is the number of species recorded area, the four major vegetation types of the Sekhukhuneland per unit area (400m2 sample plot) within a homogeneous savanna (Siebert et al. 2002) are intermingled, and include community or the total number of species per community the Combretum hereroense–Grewia vernicosa Open (Whittaker 1977). Mountain Bushveld, Kirkia wilmsii–Terminalia prunioides Cover of different layers was calculated using the cover Closed Mountain Bushveld, Acacia tortilis–Dichrostachys abundance values of the Braun-Blanquet scale. For the pur- cinerea Arid Northern Bushveld and the Hippobromus pau- pose of this study, it was assumed that R = 0.1%, + = 0.5%, ciflorus–Rhoicissus tridentata Rock Outcrop Vegetation. 1 = 2.5%, A = 8.5%, B = 18.5%, 3 = 25% cover. The percentage cover for a species in a species group was determined as Materials and Methods the sum of the cover percentages of all the relevés in the species group, divided by the number of relevés in the species Floristic and habitat data of the Mountain Bushveld have group. Cover percentage of layers for a species group was been obtained from 194 stratified random sample plots. calculated as the sum of all species cover percentages for a Stratification was based on terrain type and aspect. Plot size growth form in the species group. Four growth forms were was standardised and fixed at 20 x 20m. Within each sam- recognised, namely grass (g), forb (f), shrub (s) and tree (t). ple plot, all species were recorded and a cover-abundance Vegetation heights were based on visual estimates. South African Journal of Botany 2002, 68: 475–496 477

UNTAINS T MO OR DRAKENSBERG DPO TRY S Olifants River Lebowakgomo Potlake Nature Reserve

LIMPOPO

Penge Olifants River

Lepellane River L

M Spekboom River

U Burgersfort N

SOUTH AFRICA Limpopo T A

Sekhukhune I N Steelpoort g n

te u S a Mpumalanga North West G Jane Furse

Free KwaZulu- State Natal Spekboom River Northern Cape Steelpoort River

Eastern Cape E N Western Cape U H K

lpRiverKlip U

K Groblersdal E Lydenburg S

B Roossenekal

Steelpoort River

H T

STEENKAMPSBERG

Olifants River

Stoffberg Dullstroom

= Study Area MPUMALANGA 020 200kmkm

Figure 1: Extent of occurrence of the Open Mountain Bushveld of the Sekhukhuneland Centre of Plant Endemism in Limpopo (Northern Province) and Mpumalanga, South Africa 478 Siebert, Van Wyk and Bredenkamp

The geographical distribution of all the taxa was verified at 1.2 Enteropogono macrostachyos–Sclerocaryetum bir- the National Herbarium (PRE), Pretoria, and Schweickerdt reae rhigozetosum obovati Herbarium (PRU), University of Pretoria, to identify any taxa 2.Enneapogono scoparii–Kirkietum wilmsii endemic/near-endemic to the region (Siebert 1998). All taxa 2.1 Enneapogono scoparii–Kirkietum wilmsii grewietosum were checked against the Red Data List of southern African monticolae plants (Hilton-Taylor 1996) to determine their conservation 2.2 Enneapogono scoparii–Kirkietum wilmsii grewietosum status. All taxa indicated as undescribed species, are based flavescentis on Siebert et al. (2002a). 2.3 Enneapogono scoparii–Kirkietum wilmsii berchemietosum zeyheri Results and Discussion 2.4 Enneapogono scoparii–Kirkietum wilmsii commiphoretosum mollis An analysis of Combretum hereroense–Grewia vernicosa 2.5 Enneapogono scoparii–Kirkietum wilmsii dalechampi- Open Mountain Bushveld resulted in the identification of two etosum galpinii major vegetation units and 20 plant communities, which are 3.Setario sphacelatae–Acacietum caffrae grouped as six associations and 19 sub-associations (Table 3.1 Setario sphacelatae–Acacietum caffrae thesietosum 1). These were subsequently hierarchically classified, magalismontani described and interpreted. Approximately 500 (25%) of the 3.2 Setario sphacelatae–Acacietum caffrae myrothamne- SCPE’s approximately 2 000 known plant taxa were record- tosum flabellifolii ed during the survey of the OMB, with only the most con- 3.3 Setario sphacelatae–Acacietum caffrae melinetosum spicuous and dominant taxa presented in Table 1. The dis- nerviglumis tribution of the 44 Sekhukhuneland Centre endemic/near- 3.4 Setario sphacelatae–Acacietum caffrae argylobieto- endemic and Red Data List taxa among various plant com- sum wilmsii munities is listed in Table 1. 3.5 Setario sphacelatae–Acacietum caffrae combretetosum zeyheri Classification II.Loudetio simplicis–Eucleion linearis Plant communities of the Combretum hereroense–Grewia 4.Eragrostio lehmannianae–Hippobrometum pauciflori vernicosa Open Mountain Bushveld recognised in the SCPE 4.1 Eragrostio lehmannianae–Hippobrometum pauciflori are classified as follows (Figure 2): rhoetosum batophyllae 4.2 Eragrostio lehmannianae–Hippobrometum pauciflori I. Enneapogono scoparii–Kirkion wilmsii sorgetosum bicoloris 1.Enteropogono macrostachyos–Sclerocaryetum birreae 4.3 Eragrostio lehmannianae–Hippobrometum pauciflori 1.1 Enteropogono macrostachyos–Sclerocaryetum bir- eucleetosum crispae reae asparagetosum sekukuniensis 5.Loudetio simplicis–Eucleetum linearis

Figure 2: Dendrogram depicting the classification of the plant communities belonging to the Open Mountain Bushveld of the Sekhukhuneland Centre of Plant Endemism South African Journal of Botany 2002, 68: 475–496 479 Phytosociological table of the Open Mountain Bushveld of the Sekhukhuneland Centre Plant Endemism of the Open Mountain 1: Phytosociological table Table 480 Siebert, Van Wyk and Bredenkamp . Table 1 cont Table South African Journal of Botany 2002, 68: 475–496 481 5. 5. 6 ...... II ...... ++...... +.R...... R+...... 3. 4. 4. 4. 5. 5. ++++1R...... + . 3. ++++R++. +++R...... RR. . . . ++++++++++++++++ . . .R...... ++++ . . . . . + .R. . + . + . . . +++1 . . 1R. +1A1 . +++ .AR. 1R+. .R. . I 2. 3. 3. 3. 2...... R...++.+.+.R+....+.R+..R+.+...... R....++..++.... 1352413234 2123451234512312 ...... R++R++...... R++R+...... ++.+R+..R...... RR...... ++R.R...... +...... R.1.+R...++...... +...... +R++.+.1R+1...... R...... R.++R...... +.R+...... R...... ++R...... +...+...... +...... ++..+...++.+...... R+...... RR.....+R..R+R++.R.+...... R...... RR+.++R..R++R.+...... +..+.....++...... R..R....++..+R...R...... R...... R+.+.+...R...... +.R...... +...... +R+.+1...... R...... +R++...... R...++.R...... R...... +...... R....R.+++R...... R+...... +...+.....++R...... ++.+R....R...... R...... ++.111...... R...... +..+...... R+.+...... +R...... 1...... R+...... R..++R..R+...... R...... +.+...... R...... +...... R++.++R.++.+R1R.+R.R ...... +.R...... +.R++.+.+R+.R..++R..R...... ++.+R.R...... +R+++..R...... R...... R...... +...... +.+.R...... +R+...... R.R...... +1+.+...... +.+R.+R+.1++..++.++.+.R+...... R.....R...... R...... R.++...R+..+R..+R....++.R...... ++R...... R+R...... +R...... +R...... R.+R...... +R++R...... +...... 1.1. 2. 2. 2. 1 R...... R+.R+...... Setario sphacelatae–Acacietum caffrae argylobietosum wilmsii Setario sphacelatae–Acacietum caffrae melinetosum nerviglumis Enneapogono scoparii–Kirkietum wilmsii berchemietosum zeyheri Enneapogono scoparii–Kirkietum wilmsii commiphoretosum mollis Setario sphacelatae–Acacietum caffrae thesietosum magalismontani Setario sphacelatae–Acacietum caffrae myrothamnetosum flabellifolii Setario sphacelatae–Acacietum caffrae Enneapogono scoparii–Kirkietum wilmsii dalechampietosum galpinii ) [$] R+...... R..+.R.+..+.+R.++...RR.+...... ) S458 f g ) [$] ) f f s (form: f f [#] f f [K;$] f ) [$] ) t f f [#] S22 f f f g f f f f f f [#] f f t g f f t S1845 f f f f f g f t s [K;#] f f t s (form: f t sp. f ( Association Sub-association Alliance Berchemia zeyheri Felicia clavipilosa Species group G: Diagnostic species for Barleria wilmsiana Species group N: Preferential species for Andropogon schirensis Ruellia stenophylla Euryops transvaalensis Dolichos trilobus Pavetta zeyheri Thamnosma africana Drimiopsis atropurpurea Schistostephium heptalobum Sphedamnocarpus pruriens Argyrolobium wilmsii Ozoroa albicans Dyschoriste fischeri Stylochaeton Indigofera lydenburgensis Clerodendrum ternatum Ipomoea magnusiana Species group I: Diagnostic species for Dalechampia galpinii Barleria lancifolia Aloe verecunda Species group H: Diagnostic species for Commiphora mollis Sterculia rogersii Acacia caffra Gymnosporia senegalensis Hyparrhenia hirta Species group J: Diagnostic species for Rhynchosia spectabilis Senecio scitus Faurea saligna Cussonia transvaalensis Species group K: Diagnostic species for Jamesbrittenia macrantha Selaginella dregei Thesium magalismontanum Hermannia boraginiflora Helichrysum harveyanum Species group L: Diagnostic species for Xerophyta villosa Myrothamnus flabellifolius Gerbera ambigua Eustachys paspaloides Ceterach cordatum Eragrostis pseudosclerantha Oldenlandia herbacea Species group M: Diagnostic species for Melinis nerviglumis Plectranthus xerophilus Table 1 cont. Table 482 Siebert, Van Wyk and Bredenkamp > . Table 1 cont Table ? < = F ; E < < = < South African Journal of Botany 2002, 68: 475–496 483 ! # ! !! !" ! . O @ ; Q @ K ? R Table 1 cont Table 484 Siebert, Van Wyk and Bredenkamp ! > > . N LL Table 1 cont Table OPPPOPPPOQP OPPPPPP STPTPTPPPO PTUPT VWPTONUPUPUPTUT TPUPOX TPUPYZUPYZUPZUPZPZ NPPPP ? ? South African Journal of Botany 2002, 68: 475–496 485

5.1 Loudetio simplicis–Eucleetum linearis gnidietosum the rock types are relatively similar, local environmental con- polycephalae ditions result in slight differences in vegetation composition. 5.2 Loudetio simplicis–Eucleetum linearis blepharietosum The toxicity of the Sekhukhuneland soils is currently under saxatilis investigation at the University of Pretoria. 5.3 Loudetio simplicis–Eucleetum linearis lotononietosum The plant communities of the OMB forms part of the pro- wilmsii posed Kirkia wilmsii–Acacia caffra Order (Siebert et al. 5.4 Loudetio simplicis–Eucleetum linearis geigerietosum 2002) on ultramafic substrates and are described below. ornativae 6.Kleinio longiflorae–Raphionacmetum procumbentis I. Enneapogono scoparii–Kirkion wilmsii The alliance is classified as part of the Enneapogono sco- A vegetation key is presented to facilitate plant communi- parii–Kirkion wilmsii of Closed Mountain Bushveld [CMB] ty identification (Table 2). The definitions are broad indica- (Siebert et al. 2002b). Associations described here as part of tions of typical groups and serves as a guideline. In the key, the OMB are found predominantly on southern aspects and a characteristic of the vegetation or habitat of a plant com- those of CMB on northern aspects. munity is given, followed by one or two diagnostic and con- Habitat. As part of the OMB, the alliance is predominantly spicuous plant species. The first species is restricted to the found on cool aspects and occurs on moderate to steep specific community only, and the second is dominant, but slopes (3–15°). It prefers midslopes, but to a lesser degree also occurs in other communities. Where one species is also occurs on scarps, crests and footslopes. Soils are shal- given, no species were restricted to the community only. low and constitute rocky Mispah and Glenrosa forms. The soil surface is covered by 20–70% of rock with an average diam- Description eter of 0.2–1.5m. Table 1 summarises the habitat data for the alliance. It differs from the Loudetio simplicis–Eucleion linearis The Combretum hereroense–Grewia vernicosa Open (described in this paper), in that it is characterised by shallow Mountain Bushveld is predominantly restricted to cooler soils, an undulating topography and rocky terrain. and/or calcareous slopes of undulating ultramafic valleys, Vegetation structure. The alliance is an open, sparse, hills and mountains. Surface rocks are predominant and broad-leaved savanna of mountain slopes. Diagnostic abundant in the various habitats, with average rock size species are represented by species group R (Table 1) and varying between 200 and 1 000mm (20–70% surface cover) include the conspicuous shrubby climber Acacia ataxacan- on the slopes of hills and between 100 and 400mm (10–50% tha, shrub Ormocarpum kirkii and trees Combretum molle surface cover) in the valleys. The vegetation can be classi- and Ozoroa sphaerocarpa. Diagnostic herbaceous taxa fied as open broad-leaved woodlands and shrublands include the forbs Justicia protracta and Tephrosia purpurea, (Edwards 1983), which constitute a unique ‘island’ that dif- the fern Pellaea calomelanos and the grass Eragrostis fers significantly from the surrounding habitat and vegeta- chloromelas. Brachylaena ilicifolia, Grewia vernicosa, Tinnea tion. The classification also emphasised the dominance of rhodesiana and Triaspis glaucophylla are dominant woody the grass layer, a phenomenon also characteristic of the species. Commelina africana, Phyllanthus glaucophylla and savanna vegetation on the ultramafics of Zimbabwe (Wild Psiadia punctulata are the dominant forbs, and Heteropogon 1974, Guy 1975, Proctor and Cole 1992). contortus and Themeda triandra the dominant grasses. Two major vegetation units are recognised on the grounds Floristic diversity. Floristic links with the other alliance is of the physical environment, namely mountain slopes or val- visible in species groups W, AB, AE, AF and AG (Table 1). leys, and subsequent associated floristic composition. The weak links support the recognition of this group as an Mountain slopes are defined as the scarps, midslopes and alliance. Strong floristic links are shared with the upper footslopes of undulating norite and pyroxenite hills Enneapogono scoparii–Kirkietion wilmsii of the Closed and mountains. Valleys are defined as the low-lying areas Mountain Bushveld (Siebert et al. 2002b) and is charac- with alluvium deposits, usually traversed by a stream or terised by the small trees/shrubs Acacia senegal var. leio- river, and lower footslopes between hills and mountains. rachis, Elephantorrhiza praetermissa, Grewia monticola and Within the two major units, plant communities are deter- Triaspis glaucophylla, and the forbs Asparagus buchananii, mined by an extremely heterogeneous environment, which Commelina africana, Jasminum multipartitum and Pellaea relates to available soil moisture (combination of soil struc- calomelanos. The average number of species encountered ture, soil depth, terrain type, aspect and rockiness), geolog- per sample plot for this alliance is 38, with the total number ical substrate, heavy metal soils and anthropogenic-altered of plant species being a minimum of 232 taxa (55 relevés) areas. A summary of selected community attributes is sup- (Table 1). There are 34 plant taxa of conservation value, 21 plied in Table 1. are SCPE endemics, 12 are SCPE near-endemics and eight Associations are pronounced and easily distinguishable in are Red Data List taxa (Table 1). Of these taxa, 11 are the field, causing a distinct distribution pattern of habitats restricted to this alliance in the SCPE. and associated vegetation. This is ascribed to the geological boundaries, which can be observed as open, sparse and 1. Enteropogono macrostachyos–Sclerocaryetum bir- stunted vegetation structure that differs from surrounding reae ass. nova hoc loco vegetation. It has previously been shown that the vegetation Nomenclatural type: Relevé 413 (holotypus), Table 1 of toxic ultramafic soils (serpentine) contrasts markedly with Habitat. The association is predominantly associated with adjoining non-serpentine vegetation in its structure (Wild exposed pyroxenite and norite rock on the eastern slopes of 1974, Davie and Benson 1995, Brooks 1998). Even when the Leolo Mountains, but also occurs on exposed ferrogab- Table 2: A key to the syntaxa of the Open Mountain Bushveld of the Sekhukhuneland Centre of Plant Endemism 486

Leads/description Go to/syntaxon i. a Well-drained soils ii. b Seasonally waterlogged soils Fuirena pubescens–Schoenoplectus corymbosus Wetland Vegetation ii. a Broad-leaved savanna iii. b Microphyllous thornveld Acacia tortilis–Dichrostachys cinerea Arid Northern Bushveld iii. a Dense tree cover (mean >5%) iv. b Sparse tree cover (mean <5%) Themeda triandra–Senecio microglossus Cool Moist Grasslands iv. a Small rock size (<2m diameter) v. b Large rock size (>2m diameter) Hippobromus pauciflorus–Rhoicissus tridentata Rock Outcrop Vegetation v. a Predominantly open woodlands 1 Combretum hereroense–Grewia vernicosa Open Mountain Bushveld b Predominantly closed woodlands Kirkia wilmsii–Terminalia prunioides Closed Mountain Bushveld 1 a Slope bushveld (Ozoroa sphaerocapa & Themeda triandra) 2 b Valley bushveld (Bolusanthus speciosus & Diheteropogon amplectens) 3 2 a Sparse tree cover <4% (Acacia caffra & Berkheya insignis) 4 b Dense tree cover >4% (Kirkia wilmsii) 5 3 a Ferric soils (Raphionacme procumbens & Ozoroa sphaerocarpa) 6. Kleinio longiflorae–Raphionacmetum procumbentis b Eroded soils (Andropogon chinensis) 6 4 a Rock size <500mm (Euclea sp.) 7 b Rock size >500mm (Rhoicissus tridentata) 8 5 a East/west aspects (Enteropogon macrostachys & Croton gratissimus) 9 b North/south aspects (Combretum apiculatum & Triaspis glaucophylla) 10 6 a Erosion gulleys (Eragrostis lehmanniana & Hippobromus pauciflorus) 11 b Sheet erosion (Euclea linearis & Aristida canescens) 12 7 a Slope level (Thesium magalismontanum & Tephrosia purpurea) 3.1 Setario sphacelatae–Acacietum caffrae thesietosum magalismontani b Slope moderate (5°) (Myrothamnus flabellifolius & Aloe cryptopoda) 3.2 Setario sphacelatae–Acacietum caffrae myrothamnetosum flabellifolii 8 a Grassland elements (Argyrolobium wilmsii & Gnidia caffra) 13 b Savanna elements (Combretum zeyheri & Elaeodendron transvaalensis) 3.5 Setario sphacelatae–Acacietum caffrae combretetosum zeyheri 9 a Ferrogabbro (Asparagus sekukuniensis & Croton menyhartii) 1.1 Enteropogono macrostachyos–Sclerocaryetum birreae asparagetosum sekukuniensis b Pyroxenite/norite (Rhigozum obovatum & Combretum hereroense) 1.2 Enteropogono macrostachyos–Sclerocaryetum birreae rhigozetosum obovati 10 a Mean rock cover <40% (Aloe castanea & Rhus leptodictya) 14 b Mean rock cover >40% (Vitex obovata) 15 11 a Footslopes (Euclea crispa & Aristida congesta) 4.3 Eragrostio lehmannianae–Hippobrometum pauciflori eucleetosum crispae b Valleys (Brachylaena ilicifolia) 16 12 a Alluvium (Gnidia polycephala & Aloe cryptopoda) 5.1 Loudetio simplicis–Eucleetum linearis gnidietosum polycephalae b Alluvium/pyroxenite (Jamesbrittenia burkeana) 17 13 a Midslopes/scarps (Melinis nerviglumis & Plectranthus xerophilus) 3.3 Setario sphacelatae–Acacietum caffrae melinetosum nerviglumis b Scarps only (Argyrolobium wilmsii & Tarchonanthus camphoratus) 3.4 Setario sphacelatae–Acacietum caffrae argylobietosum wilmsii

14 a Slope 7-9° (Grewia monticola & Combretum molle) 2.1 Enneapogono scoparii–Kirkietum wilmsii grewietosum monticolae Siebert, Van Wyk andBredenkamp b Slope 3-5° (Grewia flavescens & Orthosiphon fruticosus) 2.2 Enneapogono scoparii–Kirkietum wilmsii grewietosum flavescentis 15 a Mean shrub cover >10% (Commiphora mollis & Xerophyta retinervis) 2.4 Enneapogono scoparii–Kirkietum wilmsii commiphoretosum mollis b Mean shrub cover <10% (Diospyros lycioides) 18 16 a Mean grass cover <15% (Rhus batophylla & Mimusops zeyheri) 4.1 Eragrostio lehmannianae–Hippobrometum pauciflori rhoetosum batophyllae b Mean grass cover >15% (Sorghum bicolor & Terminalia prunioides) 4.2 Eragrostio lehmannianae–Hippobrometum pauciflori sorgetosum bicoloris 17 a Magnetite (Lotononis wilmsii & Rhus wilmsii) 5.3 Loudetio simplicis–Eucleetum linearis lotononietosum wilmsii b Norite (Elionurus muticus) 19 18 a Mislopes/scarps (Berchemia zeyheri & Dombey rotundifolia) 2.3 Enneapogono scoparii–Kirkietum wilmsii berchemietosum zeyheri b Midslopes only (Dalechampia galpinii & Setaria lindenbergiana) 2.5 Enneapogono scoparii–Kirkietum wilmsii dalechampietosum galpinii 19 a Mean rock size <300mm (Blepharis saxatilis & Rhus keetii) 5.2 Loudetio simplicis–Eucleetum linearis blepharietosum saxatilis b Mean rock size >300mm (Geigeria ornativa & Aristida adscensionis) 5.4 Loudetio simplicis–Eucleetum linearis geigerietosum ornativae South African Journal of Botany 2002, 68: 475–496 487 bro on the western slopes of the same range where it is sample plot is 31, with the total number for this association semi-isolated from the rest of the SCPE. The association is being a minimum of 94 plant taxa (six relevés). associated with shallow rocky soils (Glenrosa form), usually an orthic A-horizon over a lithocutanic B (Table 1). However, 1.1 Enteropogono macrostachyos–Sclerocaryetum birreae in certain communities of the western aspects, especially the asparagetosum sekukuniensis subass. nova hoc loco lower footslopes, the Steendal form (melanic A-horizon over Nomenclatural type: Relevé 413 (holotypus), Table 1 a soft carbonate horizon) intersperse with the lithosols. The This vegetation unit comprises sparse woodlands on the shallow soils and geographic position make it the driest sys- western midslopes of the Leolo Mountains and its foothills. tem of the OMB. The topographic position is predominantly Combretum petrophilum and Pavetta eylesii are diagnostic the lower midslopes and footslopes of the mountainside. woody species of the syntaxon and their occurrence is Rock size varies, but tends to be small (400mm), but can unique for the SCPE. Diagnostic species mainly include rare cover up to 60% of the soil surface in certain areas on the species and are given in species group B (Table 1). The western slopes. grass cover is very sparse due to arid conditions; with Vegetation structure. The vegetation representing this Enteropogon macrostachys and Heteropogon contortus the association is sparse, short woodland on the lower slopes most dominant grasses. The sub-association exhibits a and foothills of the north-south trending Leolo Mountains. floristic link with the slopes of Thaba Sekhukhune (sub-asso- Diagnostic species are presented in species group A (Table ciation 2.1) (Table 1). In the OMB, this plant community has 1). Sclerocarya birrea and Croton gratissimus are diagnostic the highest number of taxa of conservation value restricted trees of the association and are also very characteristic. to it and include an endemic form of Asparagus intricatus, Other important woody species include Dichrostachys the SCPE endemic Asparagus sekukuniensis (Insufficiently cinerea and Grewia vernicosa. Tree and shrub cover are Known in the Red Data List) and the SCPE near-endemic both approximately 8% and woodies grow up to 3.5m. Combretum petrophilum (Rare in the Red Data List) (Table 3). Hibiscus coddii and Stylochaeton natalensis are the diagnostic forbs. The association is characterised by short grass 1.2 Enteropogono macrostachyos–Sclerocaryetum birreae layer, but this is well developed, with a cover of approxi- rhigozetosum obovati subass. nova hoc loco mately 37%. Enteropogon macrostachys is the diagnostic Nomenclatural type: Relevé 333 (holotypus), Table 1 grass. The eastern midslopes tend to have a much higher The vegetation type is short, open woodland on the east- cover of grasses and trees, whereas the western slopes, ern midslopes and foothills of the Leolo Mountains. which lie in the rainshadow, are characterised by a well- Diagnostic species of the association are in species group C established forb layer. (Table 1). Woody species diagnostic for the association Floristic diversity. This savanna community is rare in the includes rock outcrop elements, namely Diospyros lycioides SCPE and only a slight floristic affinity exists with other slope subsp. sericea and Vangueria infausta, the semi-succulent bushveld communities of the OMB in species groups S and shrub Senecio barbertonicus, the valley shrub Rhigozum T (Table 1). Although not many taxa of conservation value obovatum and the climber Rhoicissus tomentosus. are present in the association, there are four taxa that are Dominant woody species of the sub-association include worth mentioning (Table 1). Combretum petrophilum and Mimusops zeyheri, Mystroxylon aethiopicum and Schotia Hibiscus barnardii are both Red Data List taxa assessed as brachypetala. Although the woodland species on average Rare. In addition, two locally endemic Asparagus species, only reach 3m, it is characterised by specimens with wide which are also restricted to the association (Table 3), are crowns, which increases the combined tree and shrub cover only found along the eastern and western aspects of the to almost 20%. The tree cover percentage of 10% is the mountain. The average number of species encountered per highest value recorded for the OMB. The community has a

Table 3: Rare and endangered species restricted to specific plant communities of the Sekhukhuneland Centre of Plant Endemism

Species Family Plant communities 1.1 2.2 3.3 3.4 4.2 5.1 5.2 5.3 5.4 Argyrolobium wilmsii FABA ..##..... Asparagus intricatus [form] (W&S1501)ASPA$...... Asparagus sekukuniensis ASPAK$...... Bauhinia tomentosa [form] (S444) FABA . $ ...... Combretum petrophilum COMB R# ...... Euphorbia barnardii EUPH . . . . . E$ . . . Helichrysum uninervium ASTE ...... #.# Nuxia gracilis LOGA . . . . . K# . . . Ozoroa albicans ANAC . . K# K# . . . . . Plectranthus xerophilus LAMI ..#...... Rhus engleri ANAC ....#.... Rhus wilmsii ANAC ...... K# . Scilla natalensis LILI ...N.....

$ = endemic; # = near-endemic; R = Rare; E = Endangered; K = Insufficiently Known; N = threatened elsewhere S = Siebert; W = Van Wyk 488 Siebert, Van Wyk and Bredenkamp typical savanna structure and therefore it also has a well- servation value are part of the association, but only a form of developed grass layer with a very high cover of 31%. Bauhinia tomentosa is restricted to it (Table 3). Also consid- Grasses are mostly short (<50mm). This sub-association er the taxa listed of conservation value for this alliance in exhibits a strong floristic link with the natural, eroded CMB (Siebert et al. 2002b). Although many of the SCPE drainage gulleys of Association 4 (species group S; Table 1). endemics and near-endemics occur in this association, they The community is characterised by a low number of taxa of are also common in other associations. The average num- conservation value. ber of species encountered per sample plot is 39, with the total number of plant species being a minimum of 167 taxa 2. Enneapogono scoparii–Kirkietum wilmsii for the association (24 relevés). The association is classified as part of the Enneapogono scoparii–Kirkietum wilmsii of Closed Mountain Bushveld 2.1 Enneapogono scoparii–Kirkietum wilmsii grewietosum [CMB] (Siebert et al. 2002b). monticolae subass. nova hoc loco Habitat. The association occurs along mountain and hill Nomenclatural type: Relevé 291 (holotypus), Table 1 slopes running into the Steelpoort River Valley. The habitat of This sub-association is tall, open woodland of predomi- the association is extremely heterogeneous with no two nantly north and east facing midslopes of the Thaba relevés exhibiting the same set of environmental factors Sekhukhune and Schurinksberg, and also the associated (Table 1). It occurs on relatively steep midslopes and scarps ferrogabbro foothills between these areas. The sub-associa- on all aspects of norite and pyroxenite hills and mountains. tion is characterised by dense stands of trees that reach 5m Sub-associations also occur on scattered hills of ferrogabbro, or more and include Combretum apiculatum, C. molle and granophyre or magnetite. Rock cover and average rock size Kirkia wilmsii. Diagnostic species are presented in species vary considerably, namely 30–65% of the soil surface and a group E (Table 1). Diagnostic grasses include Chloris virga- relatively large diameter of 450–1 200mm, respectively. The ta and Eragrostis rigidior, both which are indicators of dis- association prefers rocky soils with a lithocutanic B-horizon. turbance. The sub-association is popular for cattle and game Vegetation structure. The vegetation of this association is farming and probably as a result of intensive grazing the tall, dry woodland stands that are characterised by a well- grass cover is only 15%. Northern aspects are dry and char- develop grass layer. Species group D contains the diagnos- acterised by small succulent trees of Aloe castanea and A. tic species for this association, which include the character- marlothii. The sub-association has a floristic similarity with istic trees Acacia senegal var. leiorachis, Combretum apicu- sub-association 2.2, which can be related to heavy metal latum, Dombeya rotundifolia and Ziziphus mucronata (Table soils, and this is supported by the presence of Fe-tolerant 1). Tree cover is approximately 7% and shrub cover 11%. plants in species group F (Table 1). The sub-association is The well-developed shrub layer can be ascribed to the dom- linked to association 1, in that it is characterised by the inance of species such as Brachylaena ilicifolia, Grewia absence of typical SCPE taxa of calcium-rich soils (species flava, Hippobromus pauciflorus, Triaspis glaucophylla and group Q; Table 1). The sub-association also shows a rela- Vitex obovata subsp. wilmsii. Grass cover is 19% as a result tionship with the Enneapogono scoparii–Kirkietum wilmsii of dense stands of Enneapogon scoparius, Heteropogon bridelietosum mollis of the northern aspects of ferrogabbro contortus, Themeda triandra and Panicum maximum. Trees hills (Siebert et al. 2002b). A Red Data List taxon, Rhus reach heights of up to 5m, but scattered stands of shrubs do sekhukhuniensis, is found in this sub-association (Table 1). not allow for a typical African savanna structure. Grasses are relatively tall and together with the shrub layer provides 2.2 Enneapogono scoparii–Kirkietum wilmsii grewietosum enough fuel for fires. Especially the bushveld-grassland eco- flavescentis subass. nova hoc loco tone in the Dwarsriver region has a biomass that lends it self Nomenclatural type: Relevé 271 (holotypus), Table 1 to annual fires and hence, the shrub layer is much more dis- This community represents tall, open woodland of mainly tinct than a tree layer in that area. Herbs dominate in com- pyroxenite, magnetitite and norite hills and mountains of the munities where the habitat is drier and is the most pro- Dwarsriver, Roossenekal and Leolo Mountain areas. The nounced along the scarps of hills, where succulent trees, absence of the diagnostic species presented for sub-associ- forbs and geophytes are best adapted. Total vegetation ation 2.1 in species group E characterises the community cover for the association is 45%. and preferential species are given in species group F (Table Floristic diversity. This savanna community is common in 1). Of all the Enneapogono scoparii–Kirkietum wilmsii sub- the central areas of the SCPE and a strong floristic affinity associations, this one has the highest vegetation cover per- exists with the other associations of the alliance and even centage. Dominant woody species include Acacia senegal shows a slight link with valley vegetation (Table 1). It is var. leiorachis, Brachylaena ilicifolia, Grewia flavescens and important to note that the Enneapogono scoparii–Kirkietum Terminalia prunoides. A well-developed grass layer (23% wilmsii also occurs in the Closed Mountain Bushveld [CMB], cover) occurs in and around areas with the Hutton soil type. where it is predominantly a community of north-facing Dominant grasses are Enneapogon scoparius, Heteropogon slopes (Siebert et al. 2002b). Shared characteristic species contortus and Themeda triandra. The sub-association has are the same as for the alliance, but also include the an affinity with grasslands of the Roossenekal Subcentre. trees/shrubs Combretum apiculatum, Commiphora africana, Fires are common, resulting in shrubs being the dominant C. mollis, Dombeya rotundifolia, Grewia flava, Sterculia growth form (15% cover, the highest for the OMB). rogersii and Ziziphus mucronata, and the herbaceous taxa Furthermore, a unique habitat on magnetitite with a Fe-rich Aristida meridionalis, Barleria saxatilis, Clerodendrum terna- soil environment favours heavy metal tolerant taxa (species tum and Indigofera lydenburgensis. Twenty-five taxa of con- group F, Table 1). It also shows a relationship with the South African Journal of Botany 2002, 68: 475–496 489

Enneapogono scoparii–Kirkietum wilmsii munduletosum Setaria lindenbergiana, S. sphacelata and Themeda triandra sericeae of ferrogabbro/norite hills (Siebert et al. 2002b). are the most dominant grasses. The sub-association repre- This is the only sub-association in the study area with no sents the transition to the Setario sphacelatae–Acacietum Red Data List taxa recorded for it. An endemic form of caffrae open woodlands (species group P and AE; Table 1). Bauhinia tomentosa is restricted to this community (Table 3). Furthermore, the sub-association is an ecotone between OMB and Rocky Outcrop Vegetation (Siebert et al. 2002), 2.3 Enneapogono scoparii–Kirkietum wilmsii berchemieto- and its existence as a valid sub-association of the sum zeyheri subass. nova hoc loco Enneapogono scoparii–Kirkietum wilmsii is doubtful, Nomenclatural type: Relevé 152 (holotypus), Table 1 because it is typical of the Setaria lindenbergiana This is a sub-association of southern aspects only and –Combretum molle Woodland Community of rocky outcrops representing shorter (<3.5m), open woodlands of hill slopes (Bredenkamp et al. 1994). in the Steelpoort River Valley. Diagnostic species of these habitats on scarps and upper midslopes are presented in 3. Setario sphacelatae–Acacietum caffrae ass. nova hoc species group G (Table 1). The diagnostic species of this loco community are mostly forbs, but grasses and shrubs once Nomenclatural type: Relevé 169 (holotypus), Table 1 again dominate this ecotone between grassland and The association is related to the Eustachys pas- bushveld. Berchemia zeyheri is the only diagnostic tree and paloides–Acacia caffra Woodlands of Coetzee (1975) and Dombeya rotundifolia the most dominant tree. Dominant Acacia caffra–Setaria sphacelata Woodland of Coetzee et shrub species include Brachylaena ilicifolia, Diospyros al. (1995), and is probably of the same hierarchical level. lycioides subsp. nitens, Ormocarpum kirkii, Tarchonanthus Habitat. This association is restricted to the areas south of camphoratus and Vitex obovata subsp. wilmsii. Dominant the Steelpoort River and north of Roossenekal, but with grasses include Enneapogon scoparius, Panicum deustum extensions into the Leolo Mountains. It occurs on cool, pre- and Themeda triandra. Floristic affinities for the sub-associ- dominantly southerly aspects of norite, pyroxenite and ation are the same as for the association (Table 1). An unde- anorthosite hills or mountains. It prefers midslopes and scribed, threatened endemic species, Stylochaeton sp., is scarps with clayey lithosols of the Glenrosa and Mispah recorded for this community. Plant diversity of this commu- forms. The association is common on relatively steep sloped nity is also high for the OMB, with 122 taxa recorded for the areas (5–15°). Rock cover on the surface is average, sub-association, with an average of 42 taxa per releve. between 25–60%, with rocks reaching large sizes averaging between 400–1 000mm in diameter (Table 1). 2.4 Enneapogono scoparii–Kirkietum wilmsii commiphoreto- Vegetation structure. The association is represented by sum mollis subass. nova hoc loco average (2m) to tall (5m), moist woodlands. The vegetation Nomenclatural type: Relevé 249 (holotypus), Table 1 is reasonably open, with a relatively low tree cover of 4%. This vegetation type is dry, open woodland dominated by Diagnostic woody species are the trees Cussonia trans- forbs and associated with scarps with steep slopes and vaalensis and Faurea saligna, and a suffrutex form of large rocks (Table 1). The herbaceous layer is dominant and Gymnosporia senegalensis. Diagnostic species are present- includes diagnostic forbs such as Clerodendrum ternatum ed in species group J (Table 1). The shrub layer (8% cover) and Ipomoea magnusiana, and abundant species such as is more distinct than the tree layer and includes the small Chaetacanthus costatus and Justicia protracta. Diagnostic trees/shrubs Diospyros lycioides subsp. nitens, species for this sub-association are drought tolerant and list- Elephantorrhiza praetermissa, Rhoicissus tridentata and ed in species group H (Table 1). Diagnostic trees/shrubs are Vitex obovata subsp. wilmsii. Acacia ataxacantha and Catha the semi-succulent Commiphora mollis and Sterculia roger- edulis are characteristic for the association. Forb cover is sii. Other prominent trees and shrubs include Combretum approximately 10% and well developed, and is charac- apiculatum, Elephantorrhiza praetermissa, Terminalia terised by the presence of four prominent and charasmatic prunoides and Xerophyta retinervis (form). Grass cover is forb species, namely Berkheya insignis, Gnidia caffra, reasonable when compared within the OMB. It has a floris- Jamesbrittenia macrantha and Orthosiphon fruticosus. tic relationship with the Enneapogono scoparii–Kirkietum Grass cover is 14% and characterised by the presence of wilmsii karomietosum speciosae of norite/pyroxenite hills of the grasses Setaria sphacelata and Tristachya leucothrix the Steelpoort River Valley (Siebert et al. 2002b). Fifteen with their occurrence restricted to this association and sub- plant taxa with conservation value are part of this sub-asso- association 2.5. Grasses are tall (up to 1.65m) and together ciation, but none are restricted to it. with the shrub layer provides enough fuel for fires when the surrounding vegetation burns. This association is not a con- 2.5 Enneapogono scoparii–Kirkietum wilmsii dalechampieto- tinuous vegetation type, but occurs as scattered communi- sum galpinii subass. nova hoc loco ties between large rocks in larger vegetation types such as Nomenclatural type: Relevé 283 (holotypus), Table 1 the Enneapogono scoparii–Kirkietum wilmsii. Total vegeta- Community of the distinctively grass/shrub dominated tion cover for the association is 36%. midslopes of southern aspects of hills occurring from Floristic diversity. The association occurs as small com- Burgersfort to Dwarsrivier. Diagnostic species are typical munities of scattered woodlands within other vegetation herbaceous taxa of extremely rocky slopes and are listed in types, and therefore shows distinctive floristic relationships species group I (Table 1). Dominant trees species are with association 1 and 2 in species group R, associations 2 Combretum apiculatum and Catha edulis, but regular fires and 4 in species group V and associations 4, 5, 6 and 7 in induce rapid growth of shrubs (high shrub cover of 12%). species group AD (Table 1). Of the high number of 30 taxa 490 Siebert, Van Wyk and Bredenkamp of conservation value recorded for this association, four taxa shrub cover 8%. These layers are dominated by the shrubs are restricted to it (Table 3), which includes the Wolkberg Elephantorrhiza praetermissa, Pavetta zeyheri (form), endemic species, Ozoroa albicans. Eighteen SCPE Rhoicissus tridentata and Vitex obovata subsp. wilmsii, and endemics, 11 SCPE near-endemics and six Red Data List the small trees Acacia ataxacantha, Cussonia transvaalensis taxa are found in this association. The average number of and Faurea saligna. Grass cover is relatively high, approxi- species encountered per sample plot is 39, with a minimum mately 1.65m, due to a moist habitat created by the bush- number of 170 plant taxa (25 relevés) (Table 1). clumps, and include the conspicuous grasses Diheteropogon amplectens, Heteropogon contortus, Tristachya leucothrix 3.1 Setario sphacelatae–Acacietum caffrae thesietosum and Themeda triandra. The association forms a transition magalismontani subass. nova hoc loco between the more sandy soils of sub-association 3.1 and 3.2 Nomenclatural type: Relevé 175 (holotypus), Table 1 in species group AF and the clay soils of 3.4 and 3.5 in This sub-association represents short bush clumps on the species group V (Table 1). This plant community has the crests or scarps of hills. And unlike the surrounding habitats, highest conservation value of all the sub-associations of the rocks of a relatively small size (100–300mm) cover the soil OMB. The highest number of SCPE endemics, the highest surface. Diagnostic species are presented in species group number of SCPE near-endemics, and the highest number of K (Table 1). Trees are rare (3% cover) and small (2m), and Red Data List taxa, are found in this sub-association (Table Acacia caffra is the most dominant woody species. The 1). The sub-association also has the highest average number absence of large trees can be ascribed to the strong winds of species recorded per relevé for the OMB and the highest experienced along the scarps and the high concentrations of total number of plant taxa recorded for a sub-association. chemicals in the soil due to the weathering of the rock at This richness and rarity is ascribed to the high heavy metal these exposed sites. Diagnostic herbaceous taxa are small content of these soils (Siebert et al. 2002). and inconspicuous. Berkheya insignis, Kyphocarpa angustifolia, Phyllanthus glaucophylla and Thesium magalismon- 3.4 Setario sphacelatae–Acacietum caffrae argylobietosum tanum make up the larger part of the 10% cover of the forbs. wilmsii subass. nova hoc loco Dominant taxa adapted to these harsh conditions are small Nomenclatural type: Relevé 169 (holotypus), Table 1 trees/shrubs such as Brachylaena ilicifolia, Elephantorrhiza A sub-association comprising short bush clumps with a praetermissa, Grewia vernicosa, Tinnea rhodesiana and well-developed grass layer (20% cover) on the scarps of Vitex obovata subsp. wilmsii, and the suffrutex Euclea undulating hills. The habitat is the same as for sub-associa- species. The 15% grass cover is dominated by Brachiaria tion 3.3, but is not characterised by ferrogabbro outcrops. serrata, Heteropogon contortus, Themeda triandra and No diagnostic species represent this sub-association, but Tristachya leucothrix. species group N contains the differential species of the community, which it shares with sub-association 3.3 (Table 1). 3.2 Setario sphacelatae–Acacietum caffrae myrothamneto- Important small trees/shrubs (2.25–3.5m) of the association sum flabellifolii subass. nova hoc loco are Cussonia transvaalensis, Diospyros lycioides subsp. Nomenclatural type: Relevé 237 (holotypus), Table 1 nitens, Elephantorrhiza praetermissa, Pavetta zeyheri In the OMB, this sub-association represents wooded herb- (form), Rhoicissus tridentata, Tarchonanthus camphoratus, land on exposed bedrock in already well-established wood- Vitex obovata subsp. wilmsii and Xerophyta retinervis lands. Slope has a tendency to be level, but can be up to 5° (form). Forbs are prominent in the community, but the grass- (Table 1). Species group L contains the diagnostic species for es Heteropogon contortus, Setaria sphacelata, Themeda this sub-association (Table 1). Some of these taxa are diag- triandra and Tristachya leucothrix are the most dominant. nostic species for the Myrothamnus flabellifolius–Ursinia The validity of this community as a sub-association is recog- nana Herbland of rocky flats (Smit et al. 1997). The sub-asso- nised through the absence of the taxa in species group M ciation therefore represents an ecotone between OMB and (Table 1). The second highest number of taxa of conserva- Rocky Outcrop Vegetation. Its existence as a valid sub-asso- tion value in the OMB occurs in this sub-association (Table ciation of the Setario sphacelatae–Acacietum caffrae is 1), making it one of the most important plant communities for doubtful, but is however described formally. The community conservation. Two plant taxa with conservation value are is dominated by the succulents Aloe cryptopoda and restricted to it, namely Scilla natalensis (Vulnerable in the Euphorbia schinzii, and the woody species Elephantorrhiza Free State and KwaZulu-Natal) and Ozoroa albicans praetermissa, Ozoroa sphaerocarpa and Rhus keetii. (Insufficiently Known) (Table 3).

3.3 Setario sphacelatae–Acacietum caffrae melinetosum 3.5 Setario sphacelatae–Acacietum caffrae combretetosum nerviglumis subass. nova hoc loco zeyheri subass. nova hoc loco Nomenclatural type: Relevé 208 (holotypus), Table 1 Nomenclatural type: Relevé 235 (holotypus), Table 1 This is a community represents open, sparse bush clumps This vegetation type is tall (approximately 5m), open bush on steep midslopes and scarps of cool, southern aspects clumps of cool south and east, but moderately sloped, mid- (Table 1). The soil surface is covered by relatively large rocks slopes and scarps of pyroxenite hills (Table 1). The tree of 500–1 000mm in diameter. Unlike other sub-associations, cover of 6% is the highest for the association and includes this community’s subsrate is also characterised by ferrogab- the diagnostic trees Combretum zeyheri and Elaeodendron bro. Diagnostic species are typical forbs of bushclump mar- transvaalense in species group O (Table 1). Prominent gins and are listed in species group M (Table 1). No diag- woody species of the sub-association include Combretum nostic woody species occur, but the tree cover is 5% and molle, Cussonia transvaalensis and Diospyros lycioides South African Journal of Botany 2002, 68: 475–496 491 subsp. nitens. Dominant herbaceous taxa include the forbs slopes. This vegetation type is characteristic of the large river Rhynchosia spectabilis and Senecio latifolius, and the valleys of the SCPE. It occurs predominantly as scattered grasses Heteropogon contortus, Themeda triandra and thickets in dongas or eroded areas. Soils are sandy (Hutton Tristachya leucothrix. Sixteen plant taxa with conservation form) or have a pedocutanic B-horizon (Bonheim or Valsrivier value occur in this sub-association. form) (Table 1). The habitat occurs on all aspects and is gently sloped (1–3°). Approximately 10–40% (in some instances up II. Loudetio simplicis–Eucleion linearis all. nova hoc loco to 80%) of stones cover the soil surface is and have a relatively Nomenclatural type: Loudetio simplicis–Eucleetum linearis small average diameter of between 100mm and 225mm. (holotypus), Association 5 described in this paper. Vegetation structure. Vegetation type is typical bush- The alliance is floristically related to the Tarchonanthus clumps, which gives the impression of a thicket. Preferential camphoratus–Fingerhuthia africana Transitional Woodland species are represented in species group S (Table 1). Trees of Calcareous Substrates of Van der Meulen (1979). dominate the vegetation unit (5% cover) and include the Habitat. This is an alliance of footslopes and valley bot- characteristic woody species Acacia karroo, Mimusops zey- toms of varying slope between 1° and 5° (Table 1). It is heri, Mystroxylon aethiopicum and Schotia brachypetala. restricted to deep sandy to loam soils with melanic or orthic Eragrostis lehmanniana is the dominant characteristic grass. A-horizons and calcareous lower horizons. It is found on all No taxa are diagnostic of the association. Shrub cover (6%) aspects, but predominantly southern and western aspects. and forb cover (5%) is very low in this association. Hence, Rocks can cover 10–65% of the soil surface and the mean with an average tree height of approximately 3.75m and diameter range from 100–400mm. Table 1 summarises the grass height of 1m (and cover of 17%), the association tends habitat data for the alliance. This alliance differs from the to have a typical thicket structure. It must be noted, though, Enneapogono scoparii–Kirkion wilmsii, in that it occurs on that these communities are once again scattered units with- level slopes, has deeper soils and is less rocky. in more continuous vegetation types such as the Loudetio Vegetation structure. The alliance is characterised by simplicis–Bolusanthietum speciosis. Prominent plant taxa of open bushveld anomalies of undulating footslopes and val- the association include the grasses Diheteropogon leys, which forms an extensive mosaic with the typical veg- amplectens, Loudetia simplex and Panicum deustum, and etation of such areas, namely microphyllous thornveld. the woody species Combretum hereroense, Hippobromus Species group AD contains the diagnostic species for this pauciflorus and Tinnea rhodesiana. alliance (Table 1), which includes the tree Bolusanthus spe- Floristic diversity. A strong floristic affinity exists with the ciosus, the grasses Andropogon chinensis, Aristida adscen- mountain slope bushveld in species group V (Table 1), due sionis, Elionurus muticus and Loudetia simplex, the succu- to the suitable microhabitats created for these species by the lent Aloe burgersfortensis, and forbs such as Dicoma ger- dongas (erosion gulleys). A significant relationship exists rardii, Indigofera hilaris, Polygala hottentotta, Rhynchosia with sub-association 1.2 in species group S, but this com- komatiensis and Thesium multiramulosum (Table 1). munity occurs on mountain slopes. This association has 24 Bolusanthus speciosus, in combination with dominant plant taxa with conservation value and of these, 15 are woody species such as Combretum hereroense and Euclea SCPE endemics, nine SCPE near-endemics and two are linearis, merits the recognition of this alliance, as this is a Red Data List taxa (Table 1). The average number of typical floristic composition for heavy metal soils (Wild species encountered per sample plot is 26, which is also the 1965). Other dominant species of the alliance include the lowest mean for any of the associations of the OMB. The shrubs Grewia vernicosa, Rhus keetii, Tinnea rhodesiana total number of plant species is a minimum of 105 taxa (11 and Vitex obovata subsp. wilmsii, with the herbaceous layer relevés) (Table 1). dominated by the grasses Aristida congesta, Diheteropogon amplectens, Fingerhuthia africana, Heteropogon contortus 4.1 Eragrostio lehmannianae–Hippobrometum pauciflori and Themeda triandra. rhoetosum batophyllae subass. nova hoc loco Floristic diversity. This alliance shows several floristic rela- Nomenclatural type: Relevé 166 (holotypus), Table 1 tionships with the other alliance, hence indicating that it The vegetation type occurs on the slopes of large dongas forms part of the OMB (Table 1). It also shows floristic simi- in the broad valleys to the east of the Leolo Mountains. It larities to the Great Dyke (Wild 1965) and future work might occurs on no specific aspect, where it is found on predomi- reveal a more encompassing alliance to cover the serpen- nantly deep (>1 000mm) soils of the Bonheim and Valsrivier tine areas of southern Africa. The average number of forms. The sub-association is scattered, tall (4m), but species encountered per sample plot in this alliance is sparse, thicket characterised by the diagnostic species list- approximately 32, with the total number of plant species ed in species group T (Table 1), namely the trees/shrubs being a minimum of 183 taxa (36 relevés) (Table 1). Thirty- Catha transvaalensis, Dodonaea angustifolia, Olea five taxa of conservation value are part of the alliance, com- europaea and Rhus batophylla. Other prominent woody prising 21 SCPE endemics, 14 SCPE near-endemics and species include Brachylaena ilicifolia, Combretum seven Red Data List taxa, of which 12 are restricted to it. hereroense and Hippobromus pauciflorus (tree/shrub cover is 11%). Grass cover is 11% and dominated by Aristida 4. Eragrostio lehmannianae–Hippobrometum pauciflori adscensionis, Diheteropogon amplectens, Eragrostis ass. nova hoc loco lehmanniana and Panicum deustum. Total vegetation cover Nomenclatural type: Relevé 166 (holotypus), Table 1 is the lowest for the OMB, together with the undersampled Habitat. An association that occurs on alluvium, and scat- sub-association 1.1 (two relevés). One Red Data List taxon, tered patches of exposed pyroxenite, in valleys and along foot- Rhus batophylla, occurs in this sub-association. The com- 492 Siebert, Van Wyk and Bredenkamp munity is species poor, and has some of the lowest figures the Valsrivier and Bonheim forms, but are interspersed with of total number of species per community and mean number patches of either Hutton or Mispah forms. It has the highest of species per relevé (Table 1). soil moisture in the OMB, which is ascribed to terrain type (level) and soil structure (permeable), whereby water filters 4.2 Eragrostio lehmannianae–Hippobrometum pauciflori deep into the soils after precipitation. However, most soils sorgetosum bicoloris subass. nova hoc loco dry out quickly, but carbonate (Steendal) and clay horizons Nomenclatural type: Relevé 133 (holotypus), Table 1 (Valsrivier) retain moisture and have higher moisture avail- This plant community is scattered thicket of sandy and ability over a longer period. Soil surface rock cover is aver- clay alluvium soils of the Steelpoort River valley where plate age, mainly 30–50%, with a diameter averaging between erosion has developed extensively. Diagnostic species of 100mm and 400mm. this community are represented in species group U (Table 1) Vegetation structure. This association is open, sparse and include small trees/shrubs on brackish soils, namely shrublands of sometimes very dense vegetation. The vege- Acacia leuderitzii var. retinens, Carissa bispinosa, Euclea tation type does not occur as patches and covers large divinorum, Rhus engleri and Ximenia americana. A high tree areas of land between the mountains and the Steelpoort cover of 7% is characterised by the abundance of small River, where it intersperses with short, microphyllous thorn- trees of Bolusanthus speciosus, Combretum hereroense veld or sparsely vegetated, arid areas. The diagnostic and Terminalia prunoides. The community is classified as species are represented in species group W (Table 1), with thicket due to a high frequency of intertwined shrubs such as the woody shrub species, Euclea linearis, dominating stands Carissa bispinosa and Hippobromus pauciflorus. Panicum of the association. Crabbea angustifolia, Evolvulus alsi- natalense and Sorghum bicolor are the diagnostic grasses noides, Kohautia caespitosa, Jamesbrittenia atropurpurea and contribute substantially to the 20% grass cover. Other and Ledebouria marginata are the diagnostic and prominent dominant grass taxa are Heteropogon contortus, Loudetia forbs for the association. Fingerhuthia africana is the diag- simplex and Themeda triandra. One taxon with conservation nostic grass and contributes substantially to the grass cover value is restricted to it, namely the near-endemic Rhus eng- of 16%. Other abundant grasses include Andropogon chi- leri (common on the adjacent Springbok Flats) (Table 1). The nensis, Aristida canescens, Diheteropogon amplectens, community is species poor, and has the lowest figures of Loudetia simplex and Themeda triandra. Tree cover is low total number of species per community and mean number of and dominated by Bolusanthus speciosus and Combretum species per relevé. hereroense. Shrub cover is higher (8%) and is dominated by various species, such as Rhus keetii, Tinnea rhodesiana 4.3 Eragrostio lehmannianae–Hippobrometum pauciflori and Vitex obovata subsp. wilmsii. Forbs are common and eucleetosum crispae subass. nova hoc loco have colonised this sparesely-treed habitat (13% forb Nomenclatural type: Relevé 332 (holotypus), Table 1 cover). Dicoma gerrardii, Indigofera hilaris, Petalidium In the OMB this sub-association is common on southern oblongifolium, Pterothrix spinescens and Rhynchosia koma- and western aspects of footslopes that merge into the val- tiensis are the most abundant forbs and are all characteris- leys. The habitat is characterised by erosion of the alluvium, tic taxa of sandy and/or gravel soils. which exposes layers of pyroxenite rock. This is a much Floristic diversity. The association shows slight floristic degraded system, as most of the topsoil has been washed links with other associations in species groups AB, AE and away. The system is also relatively dry as a result of its AF (Table 1). This association has one of the highest num- deep, sandy soils. The vegetation unit is open (3%), tall (4m) bers of taxa with conservation status, namely 30. Eighteen thicket. There are no diagnostic species for this sub-associ- are SCPE endemics, 12 SCPE near-endemics and of these ation and differential species are represented in species seven are Red Data List taxa (Table 1). Four taxa of conser- group V (Table 1). Grass cover is high (20%), but tree, shrub vation value are restricted to the association. The average and forb cover is relatively low. Euclea crispa is the most number of species encountered per sample plot is 35, with prominent shrub and Heteropogon contortus the most dom- the total number for this association a minimum of 122 plant inant grass. The community is species rich as a result of the taxa (21 relevés) (Table 1). exposed pyroxenite rocks, which creates a habitat suitable colonisation of mountain slope savanna species. The com- 5.1 Loudetio simplicis– Eucleetum linearis gnidietosum poly- munity is recognised on grounds of the absence of taxa from cephalae subass. nova hoc loco species groups T and U (Table 1), which are diagnostic for Nomenclatural type: Relevé 388 (holotypus), Table 1 sub-association 4.1 and 4.2, respectively. This sub-association represents the vegetation of eroded, arid, Karoo-like areas, which was originally a consequence 5. Loudetio simplicis–Eucleetum linearis ass. nova hoc of soil structure, rather than the current heavy disturbance loco by agriculture, mining and rural settlement. It is the OMB Nomenclatural type: Relevé 200 (holotypus), Table 1 vegetation unit with the deepest soils and occurs on pre- Habitat. This association is associated with Karoo-like dominantly sandy, red Hutton soils, which are interspersed areas in the larger Steelpoort River valley, a vegetation type with the Bonheim or Steendal forms in certain areas. common in eroded low-lying areas between the mountains. Species group X contains the diagnostic species for this The habitat substrate is predominantly alluvium and is sub-association (Table 1). Trees/shrubs diagnostic of the underlain by exposed norite, pyroxenite and magnetitite. It sub-association include the succulents Agave sisalana occurs on all aspects, on gentle midslopes and valley bot- (alien species) and Euphorbia tirucalli, and the rare woody toms with slopes of 1–3° (Table 1). Soils are predominantly species Nuxia gracilis and Rhus sekhukhuniensis. Aristida South African Journal of Botany 2002, 68: 475–496 493 rhiniochloa and Stipagrostis hirtigluma var. patula are the 5.4 Loudetio simplicis–Eucleetum linearis geigerietosum diagnostic grasses. Tree/shrub cover is 10% and rarely ornativae subass. nova hoc loco grows taller than 2.5m due to extensive wood harvesting. Nomenclatural type: Relevé 307 (holotypus), Table 1 Grass cover is only 11% and therefore the forb cover is well This sub-association represents open shrublands, of developed, covering 12% and growing to nearly 1m in undulating landscapes, dominated by a well-developed height. Prominent forbs include the succulent Aloe cryp- grass layer. It is mostly restricted to freely drained soils, topoda, and the herbaceous Dicoma gerrardii and unde- characterised by patches of norite and pyroxenite (with no scribed Polygala species. Four Red Data List taxa are topsoil) that has been exposed by natural erosion (Table 1). recorded for this sub-association. The Endangered endemic There are no diagnostic species for the sub-association Euphorbia barnardii, and the two disjunct Northern Cape (species group AA). The dominant species for this sub- species, Gnidia polycephala and Nuxia gracilis, are restrict- association are mainly grasses, as the grass cover is 21%. ed to this sub-association. Dominant grass species include Aristida adscensionis, Andropogon chinensis, Loudetia simplex and Themeda 5.2 Loudetio simplicis–Eucleetum linearis blepharietosum triandra. The forb layer relatively prominent (13%) and the saxatilis subass. nova hoc loco shrub layer (8%) include the conspicuous small shrubs Nomenclatural type: Relevé 200 (holotypus), Table 1 Euclea linearis and Vitex obovata subsp. wilmsii. The com- Community is an open shrubland associated with alluvium munity is recognised on the absence of taxa from species on norite and pyroxenite substrates. Sandy layers inter- groups Y and Z (Table 1), which are diagnostic for sub-asso- sperse with the Bonheim and Valsrivier soils. Diagnostic ciations 5.2 and 5.3. species are presented in species group Y (Table 1). The vegetation unit is dominated by diagnostic herbaceous species, 6. Kleinio longiflorae–Raphionacmetum procumbentis namely the succulents Euphorbia enormis and Fockea ass. nova hoc loco angustifolia, and the forbs Anthospermum rigidum, Blepharis Nomenclatural type: Relevé 284 (holotypus), Table 1 saxatilis, Cleome angustifolia and Laggera decurrens. Forb Habitat. The association occurs on scattered, small (less cover is 16% and is the highest recorded for the OMB. than 25m2) magnetitite and ferrogabbro outcrops of mid- Conspicuous small trees/shrubs are Combretum hereroense, slopes, footslopes and valleys. Outcrops are usually moder- Euclea linearis, Rhus keetii and Tinnea rhodesiana, with a ately sloped (1–7°), and are characterised by predominantly combined cover of 13% and maximum height of 3m. The shallow soils of the Mispah and Glenrosa forms. Rock cover community is dominated by the forbs Berkheya insignis, is average and approximately 30–50% of the soil surface, Dicoma gerrardii and Petalidium oblongifolium, and the with medium to small average sized stones between 250 grasses Andropogon chinensis, Diheteropogon amplectens, mm and 500mm in diameter (Table 1). Loudetia simplex and Themeda triandra. This sub-associa- Vegetation structure. The vegetation is scattered open tion has, together with sub-association 3.4, the second high- shrubland which is usually encountered amidst any of the est number of taxa with a conservation status (Table 1). None communities discussed in this paper. Diagnostic species are of these taxa are restricted to the sub-association. presented in species group AC (Table 1). There are no diagnostic trees. Forb cover (14%) is higher than the grass cover 5.3 Loudetio simplicis–Eucleetum linearis lotononietosum (12%). In addition to the prominent diagnostic forb species wilmsii subass. nova hoc loco such as Kleinia longiflora and Raphionacme procumbens, Nomenclatural type: Relevé 310 (holotypus), Table 1 other forbs such as Berkheya insignis and Petalidium In the SCPE this is open shrubland of undulating, eroded oblongifolium are dominant in the association. The com- surfaces of footslopes and valleys in the Steelpoort and bined tree/shrub cover is 6% and the maximum mean height Roossenekal regions. The habitat is characterised by patch- is 3m. The tree Combretum hereroense and the shrubs es of exposed magnetitite, hence the occurrence of gravely Grewia vernicosa and Vitex obovata subsp. wilmsii domi- Mispah soils (lithocutanic B-horizon) (Table 1). Species nate this low, sparse canopy. Diheteropogon amplectens is group Z contains the diagnostic species for this sub-associ- the characteristic grass for this association. Shallow soils ation, which are characterised by the suffrutex Rhus wilmsii and regular fires ensure that these patches of forblands pre- (Table 1). The remaining diagnostic taxa are all forbs. Forbs vail within dense Closed Mountain Bushveld. are dominant in the community and have a cover of 11%. Floristic diversity. Floristic relationships exist between this Grass cover is 14%, but the woody component is sparse association and all the others of the study area and this is with a combined shrub/tree cover of 8%. Prominent species evident in species groups AD to AG (Table 1). There are 19 of the sub-association include the shrubs Combretum plant taxa of conservation value in the association (Table 1), hereroense and Grewia vernicosa, the forb Dicoma ger- namely 11 SCPE endemics and eight SCPE near-endemics, rardii, and the grasses Diheteropogon amplectens, Loudetia of which one is a Red Data List taxon. None of these taxa simplex and Themeda triandra. The community forms a are restricted to the sub-association. The average number of unique floristic grouping with sub-associations 5.2 and 5.4 in species encountered per sample plot for this association is species group AA (Table 1), which separates these donga 36, with the total number of plant species being 81 taxa (four systems into a disturbed system (5.1) and natural systems relevés) (Table 1). (5.2–5.4). A high number of 21 taxa of conservation value were recorded for this sub-association (Table 1). 494 Siebert, Van Wyk and Bredenkamp

Conservation Bushveld and Cool Moist Grassland of the SCPE (Siebert et al. 2002). It is speculated that Enneapogono scoparii Highly degraded ecosystems, especially those in semi-arid –Kirkion wilmsii of the OMB is an unstable state, which is regions, do not recover once the stress loads are lessened maintained by a distinct environmental gradient, possibly (Rapport and Whitford 1999), for these systems are event-driv- soil moisture availability, low soil nutrient levels and high en (Ellis and Swift 1988). If the disturbance was drought, the metal/mineral concentrations in the soil. These environmen- species composition alternates between this event and the tal gradients determine the species composition of the dif- one during wetter periods. However, if this species composi- ferent plant communities of the OMB. Furthermore, the relation is changed as a result of human disturbance, the vegeta- tively high species richness of the Enneapogono sco- tion is unable to recover. This is obvious throughout the SCPE parii–Kirkion wilmsii supports its recognition as a transitional where pristine populations of indigenous plants and animals zone. Therefore, the Enneapogono scoparii–Kirkion wilmsii are under considerable pressure from exploitive land uses, discussed in this paper, contains associations that represent with old fields, heavily grazed areas, open cast mines and a transition between calcareous bushveld (Loudetio simpli- mine dumps covered by a grass layer comprising annuals and cis–Eucleion linearis) and vegetation types described by alien species infestations (Siebert and Van Wyk 2001). Siebert et al. (2002) in the following way: Fourty-four of the rare and threatened plant species of the • Enteropogono macrostachyos–Sclerocaryetum birreae — approximately 120 recorded for the SCPE (Siebert et al. transition between Loudetio simplicis–Eucleion linearis 2002a) occurs in the OMB. Certain communities in associa- and dry Hippobromus pauciflorus–Rhoicissus tridentata tions 2, 3, 4 and 5 have high numbers of rare and threatened Rock Outcrop Vegetation; species occurring within them and these are of conservation • Setario sphacelatae–Acacietum caffrae — transition value (most specifically sub-associations 2.3, 3.3, 3.4, 4.2, between Loudetio simplicis–Eucleion linearis and moist 5.1 to 5.4 and 6). Certain SCPE endemic or threatened Hippobromus pauciflorus–Rhoicissus tridentata Rock plants of the OMB are restricted to specific plant communities Outcrop Vegetation; only and therefore sub-associations such as 1.1 are also of • Enneapogono scoparii–Kirkietum wilmsii — transition conservation priority (Table 3). Most OMB associations between Loudetio simplicis–Eucleion linearis and Kirkia should be considered of conservation value as they all har- wilmsii–Terminalia prunioides Closed Mountain Bushveld. bour very unique plant communities that are restricted to the Future work should focus on the extensive habitat data SCPE and occur nowhere else in South Africa. Ultramafic available for the SCPE to determine which dynamic envi- vegetation is poorly protected in southern Africa and there- ronmental gradients contribute significantly towards the veg- fore the Sekhukhuneland OMB warrants conservation status. etation patterns of the transitional plant communities of the Conservation of many localities of the same plant com- OMB. munity in fractal landscapes (Witkowski and Liston 1997, On rocky, cool hill slopes, the Setario sphacelatae With and King 1998, Harrison 1999) is the most effective –Acacietum caffrae is a prominent, characteristic communi- approach for the protection and survival of the rare SCPE ty. This community is closely related to the Eustachys pas- taxa on ultramafic substrates. In the light of the rapid paloides–Acacia caffra Woodlands of Coetzee (1975) in the destruction of the region, certain vegetation units or areas Rustenburg region, Acacia caffra– Setaria sphacelata need immediate attention and should be considered for pro- Woodland of Coetzee et al. (1995) in the Pretoria region and tection and monitoring, as it may provide detailed historical the Setaria lindenbergiana–Combretum molle Woodland knowledge for sustainable ecosystem management Community of Bredenkamp et al. (1994) in the Potchefstroom (Swetnam et al. 1999). region. Future research is needed to determine the exact Several rare species that were recorded during the vege- extent and classification of this distinct vegetation type. tation survey are not listed in the phytosociological table due A clear floristic relationship exists between the Loudetio to their rarity in habitat (recorded in one relevé of a species simplicis–Eucleion linearis and the Tarchonanthus camphor- group). These taxa are the endemics Bauhinia tomentosa atus–Fingerhuthia africana Transitional Woodland of (form: Siebert 444), Euphorbia barnardii, Euphorbia sp. (Van Calcareous Substrates, an alliance proposed by Van der Wyk 13194), Jamesbrittenia sp. (Van Wyk 13026), the near Meulen (1979). This alliance represents plant communities endemic Kleinia stapeliiformis and the Red Data List taxon of dolomites, with which the Loudetio simplicis–Eucleion lin- Scilla natalensis. earis of this study shows strong floristic affinities (Siebert 1998). Further research should investigate the similarities Discussion between these vegetation units to determine whether they can be regarded as distinct entities or not. Much of the vegetation distribution of the OMB is associated It has been shown, that in addition to the soil type, struc- with local heterogeneous habitat conditions, which is influ- ture and depth, the soil chemistry of the study area is anoth- enced by climate, topography and soils (Siebert 1998). In er major factor responsible for the unique plant communities addition, small transient environmental changes (Sprugel that occur in these habitats (Siebert et al. 2001). Although 1991, Trollope et al. 1998) have caused large and long-last- the OMB does not lie on serpentine, but on rocks related to ing vegetation change and unstable natural vegetation pat- ultramafic substrates (Wild 1974, Roberts and Proctor terns, resulting in the subsequent unique plant communities 1992), the species have, like those on serpentine outcrops of the OMB in the study area. (Baker 1981, Reeves et al. 1983, Morrey et al. 1989), prob- It has been shown that the vegetation of the OMB shows ably adapted to the chemical composition of the soil and the a strong floristic link with both the Closed Mountain harsh, shallow-soiled, nutrient poor physical environment South African Journal of Botany 2002, 68: 475–496 495

(Siebert et al. 2001). Future research should investigate the Brooks RR (ed) (1998) Plants that Hyperaccumulate Heavy Metals. plant-soil associations in the unique plant communities of University Press, Cambridge, pp 55–94 the SCPE. Brooks RR, Malaisse F (1985) The Heavy Metal-tolerant Flora of Southcentral Africa. A.A. Balkema, Netherlands Concluding remarks Buckle C (1996) Weather and Climate in Africa. Addison Wesley Longman, Harlow Coetzee BJ (1975) A phytosociological classification of the The classification obtained by TWINSPAN and refined by Rustenburg Nature Reserve. Bothalia 4: 561–580 Braun-Blanquet procedures resulted in 20 vegetation units Coetzee JP, Bredenkamp GJ, Van Rooyen N (1995) Plant commu- (plant communities) associated with specific environmental nities of the sub-humid cool temperate Mountain Bushveld of the factors. These vegetation units should be considered as Pretoria-Witbank-Heidelberg area, South Africa. South African ecologically interpretable communities for the area con- Journal of Botany 61: 114–122 cerned. Nine syntaxa (plant communities) have been identi- Davie H, Benson JS (1995) The serpentine vegetation of the Woko- fied as of high conservation priority. Glenrock region, New South Wales, Australia. In: Jaffre T, Reeves It is hoped that the descriptions of the different vegetation RD, Becquer T (eds) The Ecology of Ultramafic and Metalliferous units will make a significant contribution towards the under- Areas. Centre de Noumea, Orstrom, pp 155–162 Edwards D (1983) A broad-scale structural classification of vegeta- standing of the association between plant communities and tion for practical purposes. Bothalia 14: 705–712 ultramafic substrates in the SCPE and southern Africa as a Ellis JE, Swift DM (1988) Stability of African pastoral systems: whole. OMB is characterised by a naturally tree depauperat- Alternate paradigms and implications for development. Journal ed flora, dominated by a low diversity of small trees/shrubs of Range Management 41: 450–459 and many taxa not typical for the region. As Brooks (1998) Erasmus JF (1985) Rainfall deciles for the Transvaal Region. Soil rightly stated, it is clear that the ‘serpentine problem’ is far and Irrigation Research Institute Report GB/A/87/18, Pretoria, pp from solved and much work remains to be done before it can 147–216 be established with certainty why peculiar plant communities Fischer HS (2000) Multivariate analysis of phenological data. can be found over ultramafic rocks. Phytocoenologia 30: 477–480 The floristic and environmental data supplied in this paper Guy PR (1975) Notes on the vegetation types of the Zambezi Valley, Rhodesia, between the Kariba and Mpata Gorges. Kirkia 10: can be meaningfully applied in the management and con- 543–557 servation of priority areas in the SCPE. Proper and sound Harrison S (1999) Local and regional diversity in a patchy land- future assessment of the region’s vegetation should include scape: native, alien, and endemic herbs on serpentine. Ecology aspects such as species rarity, habitat preference and veg- 80: 70–80 etation dynamics. These aspects are important as it relates Hennekens S (1996a) TURBOVEG: Software package for input, to the formal description and conservation requirements of processing, and presentation of phytosociological data. User’s still to be described endemic taxa which may well include guide. IBN-DLO, Wageningen. University of Lancaster, Lancaster edaphic specialists with a vast economic potential. Hennekens S (1996b) MEGATAB: A visual editor for phytosociological tables. Version 1.0. Giesen and Geurts, Ulft Acknowledgements — The authors wish to thank Ms Martie Hill MO (1979) TWINSPAN — a FORTRAN program for arranging Dednam, HGWJ Schweikerdt Herbarium (PRU), for the processing multivariate data in an ordered two way table by classification of of plant specimens, and the Curator and staff of the Pretoria individuals and attributes. Cornell University, Ithaca, New York National Herbarium for assistance with plant identification. Special Hilton-Taylor C (1996) Red Data List of Southern African Plants. thanks to Ms Franci du Plessis from the Department of Botany, Strelitzia 4. National Botanical Institute, Pretoria University of Pretoria, for assisting with the numerical analysis. The Iturralde RB (1995) The serpentine flora of Cuba: its diversity. In: National Research Foundation, the University of Pretoria, the Jaffre T, Reeves RD, Becquer T (eds) The Ecology of Ultramafic Mellon Foundation and the Department of Environmental Affairs and and Metalliferous Areas. Centre de Noumea, Orstrom, pp Tourism financially supported the research. 139–145 Jaffré T (1980) Etude Ecologique du Peuplement Végétal des Sols Dérivés de Roches Ultrabasiques en Noevelle Calédonie. References Orstrom, Paris Johnston WR, Proctor J (1981) Growth of serpentine and non-ser- rd Acocks JPH (1988) Veld types of South Africa 3 ed. Memoirs of pentine races of Festuca rubra in solutions simulating the chemi- the Botanical Survey of South Africa 57: 1–146 cal conditions in a toxic serpentine soil. Journal of Ecology 69: Baker AJM (1981) Accumulators and excluders — Strategies in the 855–869 response of plants to heavy metals. Journal of Plant Nutrition 3: Kent LE (ed) (1980) Stratigraphy of South Africa: Lithostratigraphy 643–654 of the Republic of South Africa, South West Africa/Namibia and Bedward M, Pressey RL, Keith DA (1992) A new approach for the Republics of Transkei, Bophuthatswana, Venda. Government selecting fully representative reserve networks: addressing effi- Printer, Pretoria ciency, reserve design and land suitability with an iterative analy- Kent M, Ballard J (1988) Trends and problems in the application of sis. Biological Conservation 62: 115–125 classification and ordination methods in plant ecology. Vegetatio Bredenkamp GJ, Bezuidenhout H, Joubert H, Naude C (1994) The 78: 109–124 vegetation of the Boskop Dam Nature Reserve, Potchefstroom. Land Type Survey Staff (1987) Land types of the maps 2526 Koedoe 37: 19–33 Rustenburg, 2528 Pretoria. Memoirs on the Agricultural Natural Breebaart L, Deutschlander M (1997) The vegetation types and Resources of South Africa No. 8. Department of Agriculture and management units of Goedverwacht farm in the mixed bushveld Water Supply, Pretoria of the Northern Province, South Africa. Koedoe 40: 19–33 Land Type Survey Staff (1988) Land types of the maps 2426 Brooks RR (1987) Serpentine and its Vegetation: A Multidisciplinary Thabazimbi, 2428 Nylstroom. Memoirs on the Agricultural Natural Approach. Croom Helm, London 496 Siebert, Van Wyk and Bredenkamp

Resources of South Africa No. 10. Department of Agriculture and Siebert SJ, Van Wyk AE, Bredenkamp GJ (2002) The physical envi- Water Supply, Pretoria ronment and major vegetation units of the Sekhukhuneland Land Type Survey Staff (1989) Land types of the maps 2530 Centre of Plant Endemism. South African Journal of Botany Barberton. Memoirs on the Agricultural Natural Resources of 68: 127–142 South Africa No. 13. Department of Agriculture and Water Supply, Siebert SJ, Victor JE, Van Wyk AE, Bredenkamp GJ (2002a) An Pretoria assessment of threatened plants and conservation in Loock AH, Schneider MB, Fitzpatrick RW (1982) Distribution of lim- Sekhukhuneland. PlantLife 26: 7–18 ing resources in relation to acid soils in South Africa (1:2 500 Siebert SJ, Van Wyk AE, Bredenkamp GJ (2002b) Vegetation ecol- 000). Government Printer, Pretoria ogy of Sekhukhuneland, South Africa: Kirkia wilmsii–Terminalia Low AB, Rebelo AG (eds) (1996) Vegetation of South Africa, prunioides Closed Mountain Bushveld. South African Journal of Lesotho and Swaziland. Department of Environmental Affairs and Botany 68: 497–517 Tourism, Pretoria Smit CM, Bredenkamp GJ, Van Rooyen N, Van Wyk AE, Combrinck MacVicar CN, Bennie ATP, De Villiers JM (1991) Soil Classification: JM (1997) Vegetation of the Witbank Nature Reserve and its A Taxonomic System for South Africa. Department of Agricultural importance for conservation of threatened Rocky Highveld Development, Pretoria Grassland. Koedoe 40: 85–104 Madulid DA, Agoo EMG (1995) Assessment of the vegetation of South African Weather Bureau (1998) Unpublished report. Philippine mountains on ultramafic rocks. In: Jaffre T, Reeves RD, Department of Environmental Affairs and Tourism, Pretoria Becquer T (eds) The Ecology of Ultramafic and Metalliferous Sprugel DG (1991) Disturbance, equilibrium, and environmental Areas. Centre de Noumea, Orstrom, pp 113–118 variability: What is ‘natural’ vegetation in a changing environ- Matthews WS, Bredenkamp GJ, Van Rooyen N (1992) The vegeta- ment? Biological Conservation 58: 1–18 tion of the dry dolomitic regions of the north-eastern mountain Swetnam TW, Allen CD, Betancourt JL (1999) Applied historical sourveld of the Transvaal escarpment, South Africa. ecology: Using the past to manage the future. Ecological Phytocoenologia 20: 467–488 Applications 9: 1189–1206 Morrey DR, Balkwill K, Balkwill M-J (1989) Studies on serpentine Trollope WSW, Trollope LA, Biggs HC, Pienaar D, Potgieter ALF flora: Preliminary analyses of soils and vegetation associated with (1998) Long-term changes in the woody vegetation of the Kruger serpentine rock formations in the southeastern Transvaal. South National Park, with special reference to the effects of elephants African Journal of Botany 55: 171–177 and fire. Koedoe 41: 103–112 Mucina L, Bredenkamp GJ, Hoare DB, McDonald DJ (2000) A Van der Meulen F (1979) Plant sociology of the western Transvaal national vegetation database for South Africa. South African Bushveld, South Africa. Dissertationes Botanicae 49: 1–191 Journal of Science 96: 497–498 Van Wyk AE, Smith GF (2001) Regions of Floristic Endemism in Mueller-Dombois D, Ellenberg H (1974) Aims and Methods of Southern Africa: A Review with Emphasis on Succulents. Umdaus Vegetation Ecology. Wiley, New York Press, Pretoria Proctor J, Cole M (1992) The ecology of ultramafic areas in Van Wyk AE, Van Wyk P (1997) Field Guide to Trees of southern Zimbabwe. In: Roberts BA, Proctor J (eds) The Ecology of Areas Africa. Struik Publishers, Cape Town with Serpentinized Rocks. Kluwer Academic Publishers, The Visser DJL, Coertze FJ, Walraven F (1989) Explanation of the 1: Netherlands, pp 313–331 1 000 000 geological map, 4th ed. 1984: The Geology of the Rapport DJ, Whitford WG (1999) How ecosystems respond to Republics of South Africa, Transkei, Bophuthatswana, Venda and stress: Common properties of arid and aquatic systems. Ciskei and the Kingdoms of Lesotho and Swaziland. Government BioScience 49: 193–203 Printer, Pretoria Reeves RD, Brooks RR, Dudley TR (1983) Uptake of nickel by Weber HE, Moravec J, Theurillat J-P. (2000) International Code of species of Alyssum, Bornmuellera, and other genera of old world Phytosociological Nomenclature 3rd ed. Journal of Vegetation tribus Alysseae. Taxon 32: 184–192 Science 11: 739–768 Retief E, Herman PPJ (1997) Plants of the Northern Provinces of Werger MJA, Wild H, Drummond BR (1978) Vegetation structure South Africa: Keys and Diagnostic Characters. Strelitzia 6. and substrate of the northern part of the Great Dyke, Rhodesia: National Botanical Institute, Pretoria Environment and plant communities. Vegetatio 37: 79–89 Rhoads AF, Thompson L (1992) Integrating herbarium data into a Westhoff V, Van der Maarel E (1978) The Braun-Blanquet approach. geographic information system: requirements for spatial analysis. In: Whittaker RH (ed) Classification of Plant Communities. Junk, Taxon 4: 43–49 The Hague, pp 287–399 Roberts BA, Proctor J (1992) The Ecology of Areas with Whittaker RH (1977) Evolution of species diversity in land commu- Serpentinized Rocks. Kluwer Academic Publishers, Dordrecht nities. Evolutionary Biology 10: 1–67 Roberts BA, Rodenkirchen H (1995) Soils and plant nutrition on a Wild H (1965) The flora of the Great Dyke of southern Rhodesia with serpentinized ridge in south Germany. In: Jaffre T, Reeves RD, special reference to the serpentine soils. Kirkia 5: 49–86 Becquer T (eds) The Ecology of Ultramafic and Metalliferous Wild H (1974) Variations in the serpentine floras of Rhodesia. Kirkia Areas. Centre de Noumea, Orstrom, pp 211–212 9: 209–232 Siebert SJ (1998) Ultramafic Substrates and Floristic Patterns in With KA, King AW (1998) Extinction thresholds for species in fractal Sekhukhuneland, South Africa. MSc. Thesis, University of landscapes. Conservation Biology 13: 314–326 Pretoria, South Africa Witkowski ETF, Liston RJ (1997) Population structure, habitat pro- Siebert SJ, Van Wyk AE (2001) Sekhukhuneland: Floristic wealth file and regeneration of Haworthia koelmaniorum, a vulnerable versus platinum and chromium riches. Veld & Flora 87: 168–173 dwarf succulent endemic to Mpumalanga, South Africa. South Siebert SJ, Van Wyk AE, Bredenkamp GJ (2001) Endemism in the African Journal of Botany 63: 364–370 flora of ultramafic areas of Sekhukhuneland, South Africa. South African Journal of Science 97: 529–532

Edited by L Mucina