The vegetation ecology of the Eastern Transvaal Escarpment in the Sabie area. 2. Floristic classification

The indigenous vegetation of the Eastern Transvaal Escarpment in the Sabie area is classified with the aid of the PHYTOTAB program package. Four ecological-formation classes (efc) based on floristics. physiognomy and climate correspond to four data subsets. Plant communities in each efc are defined by means of 46 differential species-groups distributed amongst forest, thicket, woodland, shrubland and grassland structural types. Environmental correlation is facilitated by means of 21 habitat types.


INTRODUCTION
To facilitate land-use planning and management of the Eastern Transvaal Escarpment on a regional and sub regional basis, the scale of Acocks's (1975) veld types needs to be enlarged (Van der Meulen & Scheepers 1978).A more detailed classification of Veld Types 8 (North-Eastern Mountain Sourveld) and 9 (Lowveld Sour Bushveld) is therefore required.Floristic classifica tions express relationships between plant communities and their environment and are thus potentially suitable planning tools.This paper describes a detailed floristic classification of Veld Types 8 and 9 in the Sabie area, within the environmental context established by Deall et al. (1989).The classification is purely descriptive and predictive, implying no explanation of causality.

METHODS
The study area comprises a broad transect whose lo cality and physical environment are described compre hensively by Deall et al. (1989).Within the transect 251 quadrats (measuring 10 x 20 m each) were distributed subjectively amongst 50 different physiognomic/land type stratification units based on 1: 250 000 Land Type Series 2530 Barberton.The quadrats were distributed as follows: 46 in forest, 64 in thicket, 76 in woodland, nine in shrubland and 56 in grassland [physiognomy based on Edwards's (1983) formation classes].In each quadrat, all plant species were listed together with their Domin-Krajina cover-abundance values and growth forms (Deall 1985).The total canopy cover and estimated height range of each stratum of vegetation was also recorded for the purpose of physiognomic-structural classification (Edwards 1983).Environmental parame ters recorded for each quadrat include the following: (i) Climatic Belt, based on altitudinal distribution of mist (cf.Deall et al. 1989).
(v) Exposure in terms of the degree of exposure to sun and wind, expressed as sheltered, partly sheltered or exposed.
(vii) Rock cover based on the degree of limitation on mechanical utilization (cf.Van der Meulen 1979).
By means of selected programs in PHYTOTAB (Westfall et al. 1982), a provisional phytosociological classification was made on the basis of the entire data set (251 relevés and 1 043 species, including unidentified specimen numbers).Four data subsets were then identi fied on the basis of floristic and environmental disconti nuity (Deall 1985).Species in each subset were then reclassified within the confines of their subset distribu tion (Coetzee 1983).Thus, both the number of syntaxa (represented by relevé-groups) and the species defining them (represented by differential species-groups), were increased relative to the provisional classification.For the sake of brevity, poorly-defined syntaxa were re moved.leaving only those that are clearly defined by Bothalia 19.1 (1989 differential species-groups.Both non-differential species and species-groups defining more than a single syntaxon were also removed*.Syntaxa were reduced to single columns by transforming the cover-abundance values of differential species to constancy values thereby creating synoptic tables (Deall 1985).

RESULTS
The four data subsets correspond to four ecologicalformation classes (efc) based on floristics, physiognomy and climate (especially mist).Each efc is represented by a synoptic table (Tables 2,4,6 & 8).The syntaxa in each efc are informally ranked as communities and are grouped according to habitat type (Tables 1, 3, 5 & 7).
Communities are named according to the recommen dations for a standardized South African syntaxonomic nomenclature system proposed by the Botanical Research Institute, Pretoria (Scheepers et al. MS).Each name comprises a differential species followed by a dominant species and a physiognomic-structural term (Edwards 1983).
Further information on species mentioned in the text but not included in synoptic tables is documented in an annotated checklist (Deall & Backer 1989).
In instances where plants could not be identified be yond the generic level, the epithet sp. is appended (e.g.Combretum sp.).It should be noted that such a name may not necessarily refer to a consistent species concept, but may include various species within the genus.Differential species are not listed in the community descriptions which follow but are referred to in the syn optic tables instead (Tables 2,4,6 & 8).

WOODLAND AND XERIC THICKET OF THE LOW COUNTRY
Xeric Thicket (Table 3) refers to the 'scrubby' type of thicket normally associated with the Low Country.Asso ciated communities are represented mainly on xeroclinal upper slopes and midslopes underlain by Nelspruit Gran ite or Transvaal Diabase.Widespread on Foothills and Escarpment Lower Slopes (Figure 7).Differential and dominant species are indicated in Table 4 (Group K).Non-differential domi nants include Cheilanthes viridis var.viridis.

WOODLAND AND SHRUBLAND OF THE MISTBELT
Associated communities are evenly distributed be tween Humid and Subhumid Mistbelts (Table 5).

GRASSLAND OF TH E M ISTBELT
Associated communities are all fire-maintained, oc curring on exposed sites with low rock cover.They are represented over all geological substrates.Table 7.

Humid Mistbelt grasslands of Escarpment
Slopes overlying Nelspruit Granite (more than 75 % vegetation cover)  ,5 o •g r : sr  (communities), defined on the basis of differential spe cies.Environmental correlation enhances the descriptive and predictive value of the classification.As a planning and management tool, however, it is obviously incom plete.Aspects such as causality and community function must yet be investigated in association with relevant key questions.The floristic classification presented here should provide a basis for such investigation.

c. 29
Clutia monticola-Umdetia simplex Low Open Woodland Widespread on xeroclinal upper slopes.Differential species are indicated in

Table 1 )
refers to a denser, more lush type of thicket which normally occurs in the Mistbelt.
* Full phytosociological tables arc nevertheless available on request from the Vegetation Ecology Division, Botanical Research Institute.Private Bag X 101, Pretoria 0001.

Humid Mistbelt forest associated with Timeball Hill Shale and Klapperkop Quartzite
Where it occurs in the Low Country, it is usually in mesic situations, i.e. riparian or south-facing.Total vegetation cover is usually more than 75 %.Associated communities are represented throughout the altitudinal range but are notably absent on the Summit Peak and on the Escarpment and Summit Plateaux.

Exposed woodlands and shrublands with less than 50 % vegetation cover and high rock cover (usually granite sheet rock)
c.22 Ceratotheca triloba-Bequaertiodendron magalismontanum Low Open Woodland Occurring mainly on Upper Foothills and Escarpment Lower Slopes.Differential species are indicated in Table 4 (Group J).Dominant species include Combretum molle and Loudetia simplex.

Humid Mistbelt grasslands of Lower Mountain Slopes c
Asclepias crassinerxis-Andropogon schirensis Short Closed Grassland Situated on mesoclinal terraces overlying Black Reef Quartzite with low rock cover, notably in Spitskop For est Reserve.Differential species are indicated in Table 8 (Group G).Dominant species include Themeda triandra..42Lippia javanica-Loudetia simplex Short Closed Grassland Tall Open Shrubland Occurring on xeroclinal slopes overlying Upper Dolo mite with low rock cover, Vertroosting Nature Reserve.Differential species are indicated in Table 8 (Group H).Dominant species include Themeda triandra and Hemizygia transvaalensis.Conglomerate with low rock cover.Differential and dominant species are indi cated in Table 8 (Group I).Non-differential dominants include Themeda triandra, Loudetia simplex and Erio sema ellipticifolium.

Mistbelt grasslands overlying Hek poort Andesite with high rock cover and xero clinal aspect c
.46 Erica atherstonei-Harpochloa falx Low Closed Grassland/Open (grassy) Shrubland Confined to upper slopes of the Summit Peak, at Mount Anderson.Differential and dominant species are indicated in Table 8 (Group L).Non-differential domi nants include Rendlia altera, Festuca costata var.cos tata, Protea parvula and Erica cerinthoides var.cerinthoides.