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Plant communities of the Ad land type in the Newcastle – Memel – Chelmsford Dam area
S.AfrJ.Bot., 1993, 59(2): 116 - 122
116
Plant communities of the Ad land type in the Newcastle - Memel - Chelmsford Dam area C.M. Smit,* G.J. Bredenkamp and N. van Rooyen Department of Botany, University of Pretoria, Pretoria, 0002 Republic of South Africa Received 12 August 1992; revised 27 October 1992
The Ad land type in the Newcastle - Memel - Chelmsford Dam area comprises areas of the plateau of the Low Drakensberg range and is associated with the Fa and Ca land types. Seventeen releves were compiled in this land type, which were firstly numerically classified (TwINsPAN) and the results of this classification were further refined by Braun-Blanquet procedures. Three major plant communities and seven subcommunities were recognized. The Themeda triandra - Monocymbium ceresiiforme grassland can be regarded as the most extensive vegetation type in this land type . A description, ecological interpretation and hierarchical classification of the plant communities are presented. Die Ad-Iandtipe van die Newcastle - Memel - Chelmsforddamgebied maak dee I uit van die plato van die Lae Drakensbergreeks en is geassosieer met die Fa- en Ca-Iandtipes. Sewentien releves is in hierdie landtipe saamgestel wat eers numeries geklassifiseer (TWINSPAN) is. Die resultate van hierdie klassifikasie is verder met behulp van Braun-Blanquetprosedures verfyn. Drie hoofgemeenskappe en sewe onderverdelings is ge·identifiseer, waarvan die Themeda triandra - Monocymbium ceresiiforme-grasveld as die hoofplantegroeitipe van die landtipe beskou kan word. 'n Hierargiese klassifikasie, beskrywing en ekologiese interpretasie van die plantgemeenskappe word aangebied.
Keywords: Ad land type, Braun-Blanquet procedures, numerical classification, ecological interpretation, grassland . • To whom correspondence should be addressed.
Introduction Mentis and Huntley (1982) and Scheepers (1986) stated the necessity to identify, describe and classify the major vegetation types within the Grassland Biome of South Africa. Besides being able to make a contribution to grassland veld management programmes, the Grassland Biome Project aims at producing a vegetation map on a 1:250000 scale (Scheepers 1986). Land types, as identified by the Land Type Survey Staff (1984, 1990), are used as stratification units. Parameters distinguishing one land type from another are terrain morphology, soil pattern/types and climate (Land Type Survey Staff 1984). The phytosociological classification of the vegetation of the Ad land type of the Newcastle - Memel - Chelmsford Dam area forms part of the Grassland Biome Project. According to Acocks's (1953, 1988) map and description, this area is classified as 'Highland Sourveld' (44a). The closest description of Edwards (1967) which conforms to the vegetation encountered in the Ad land type within the study area, is the 'Themeda - Trachypogon Highlands Grassland', especially the 'Low Drakensberg and Biggarsberg Faciation'. As these studies are of a large scale and done a considerable length of time ago, the need arose to do a more comprehensive phytosociological study of this particular area. The Ad land type in the study area is almost inaccessible, and is therefore totally undeveloped. As far as agriculture is concerned, it is only used for grazing; no ploughed fields were observed.
The study area The study area is situated between 27°33' and 28°00' S
latitude and 29°33' and 300 00'E longitude, in the Grassland Biome of north-western Natal, South Africa. The Ad land type in the study area occurs at an altitude of 1800 2000 m and its position is indicated in Figure 1. A detailed description of the physical environment was given by Smit (1992). Soils Most of the soils in this land type are shallow and of the Mispah soil form, although the Clovelly soil form has been recorded in a few instances. The soil classification nomenclature conforms to that of MacVicar et al. (1977). According to the Land Type Survey Staff (1984), the 'A' map units refer to yellow and red soils without water tables and to land which does not qualify as a plinthic catena. In the Ad land type in particular, yellow, dystrophic and/or mesotrophic soils occupy a larger area than high base status red-yellow apedal soils. Topography
The Ad land type in the study area consists mainly of the Free State Plateau (Van der Eyck et al. 1969), topping the Low Drakensberg range. To the east the Ad land type is in close association with the Fa land type [where rocky soils with Glenrosa or Mispah soil forms predominate, with lime absent in the entire landscape (Land Type Survey Staff 1984)], which forms the escarpment of the Low Drakensberg. To the west it is in close association with the Ca land type [where a plinthic catena, with duplex and/or margalithic soils, predominates (Land Type Survey Staff 1984)], which consists mainly of a plateau with incised valleys of
S.AfrJ.Bot., 1993, 59(2)
117
o
SCALE:
~.
5
10
15
20 KM
_ _..:L..'- - - - - - , ' - - - - - - ' - '- - - "
.... . ............ []J . .
Bb land type
Fa land type
.............. .. ......... [ill[] ................ .............. ..... ...... .
Ea land type
Ad land type
tr@n~nd
Ac land type
a . . . . . . . . ..
..
.. .
. ..
.......
........... e . . .. '
..
Ca land type Drainage lines
Immllllll:l:~ll:lli
Roads Bd land type --~
...
Natal/OFS border
I/ItI
Ncandu Forest Reserve
<.
Marshland
Zeekoeivlei
Border of study area
•
Approx. position of section A (Figure 2)
Figure 1 Position of the Bb, Bel, Fa, Ea, Ac, Ad and Ca land types in the Newcastle - Memel - Chelmsford Dam area (adapted from 1:250000 Land Type Series, 2728 Frankfort, Soil and Irrigation Research Institute, 1984).
streams draining into the Vaal River system (Figure 1) . The topography on the plateau is not all very gentle, but is dotted with hills and ridges, e.g. the Union Butte, one of the high-
est points in the study area, The terrain type of the Ad land type is classified as A3 (Land Type Survey Staff 1990). 'A' means that more than
S.-Afr.Tydskr.Plantk.• 1993.59(2)
118
80% of the area has slopes less than 8% and '3' indicates local relief, which in this case means that the difference between the highest and lowest pQints in the landscape varies between 90 and 150 m (Land Type Survey Staff 1984). Geology The geology of the entire study area was discussed by Smit (1992). The Middle Beaufort Stage (Visser & Bishopp 1976) is represented in the Ad land type in the study area and consists mainly of sandstone and grit, with small areas of dolerite. At Normandien Pass (Figure 1) are carbonaceous and iron-rich shale partings. Climate According to the description of the climate of the entire study area by Smit (1992), the Ad land type belongs to the area referred to as 'Mountain Regions'. The climate of this area conforms to Phillips's (1973) Bioclimatic Group 4, in which the mean annual precipitation is 1120 mm and the mean annual temperature 14°C. The highest mean daily maximum temperature of 24°C was recorded in January and the lowest mean daily minimum temperature of O°C was recorded in July (Schulze 1982; Weather Bureau 1990). Methods Over the entire study area, releves were compiled in 282 stratified random sample plots. Stratification was firstly based on land type. The number of sample plots allocated to the various land types recognized in the area, was determined pro rata and on an area basis. In this way 17 sample plots were placed in the Ad land type. Stratification within the land type was defined on terrain units. The small number of releves can be ascribed to the inaccessability of the area and to the fact that the Ad land type comprises only approximately 8% of the study area. For grassland vegetation, plot size was 10 X 10 m (Bredenkamp 1975), and for woodland 10 X 20 m (Bredenkamp 1982). Contour profiles were drawn from 1:50 000 topocadastral maps (Figure 2), in order to illustrate the terrain types of the area. Five terrain units were recognized on which stratification was based, namely 1 (crest), 2 (scarp), 3 (midslope), 4 (foots lope) and 5 (valley bottom or flood plain). The single- as well as the multi-phase terrain types were recognized (Land Type Survey Staff 1984). The Braun-Blanquet cover-abundance scale (MuellerDombois & Ellenberg 1974) was used to record the total floristic composition in each sample plot. Habitat
information such as geology, topography, topographic position, soil form and series, rockiness, rock size and vegetation structure were also recorded. Vegetation structure was classified according to Edwards's (1983) system and the predominant structural classification of the recognized plant communities is used in the name of each plant community. Taxa names conform to those of Gibbs Russell et al. (1985, 1987, 1990). The first step in classification of the floristic data was to apply Two-way Indicator Species Analysis (TwINS PAN) (Hill 1979) to the data, which resulted in a first approximation of the vegetation types of the area. This classification was then further refined with Braun-Blanquet procedures (Westhoff & Van der Maarel 1978; Behr & Bredenkamp 1988). The final results are presented in a phytosociological table (Table 1). Results Classification The vegetation of the Ad land type is mainly grassland of which the Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland is the most extensive grassland community, not only in the Ad land type, but also in the Bb (Smit et al. 1992), Fa (Smit et al. 1993a) and Ac (Smit et al. 1993b) land types. Each land type though, reveals its own subcommunities and variants of this broad Themeda triandra - Monorymbium ceresiiforme grassland. Subcommunities of this grassland are associated with soil depth and rockiness. Three other communities on extremely rocky habitats were also recognized. Woody vegetation is sparse and when present, stunted. These grasslands are known as 'sourveld' or fire climax grasslands, which means that the grassland stage is maintained by the regular occurrence of fire (Tainton 1981). It seems as though altitude and exposure may be causal factors for the sparse occurrence and stunted growth of trees and shrubs and not solely fire as management tool. The communities were hierarchically classified as follows: 1. The Tristachya leucothrix - Aristida congesta subsp.
congesta Low Closed Grassland on flat sandstone outcrops. 2. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland 2.1 The Themeda triandra - Scilla nervosa Low Closed Grassland on deep, non-rocky soils. 2.2 The Themeda triandra - Gnidia kraussiana Low Closed Grassland on shallow, sandy Mispah soils.
A
:§ 1905
Ad
I
27"53'36·S
I
I _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .l_ 29·41 10u E
Figure 2 Contour profiles of the Ad land type at 2r53'36"S latitude. showing its relation to the Ca and Fa land types (South Africa 1:50000 sheet 2729 Mont Pelaan).
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S.AfrJ.Bot., 1993, 59(2)
Table 1 A phytosociological table of plant communities in the Ad land type in the Newcastle - Memel - Chelmsford Dam area a
RELEVES
0000 9999 1345
9 2
2 1 6
0120 9439 7626
11 22 23
122 233 101
2
11 44 37
1
2.1
2 ·2
2.3
2. 4
3. 1
3. 2
1 + + +
++
3 + +
3323 ++ + + + +
+
+
Species group B 3
+1 + + ++
+
+ +
+++ ++
+
+
+
+ +
122 233 101
1
11 44 37 3
2.3
2. 4
3.1
3. 2
Helichrysum chionosphaerum Gazania krebsiana Monsonia attenuata Scabiosa col umbari a Crassllla pellllcida Ellryops transvaalensis Senecio rhomboidells Microchloa caffra Andropogon appendiclllatus Eragrostis plana Gladiollls permeabilis Delosperma gracile
+1 ++ ++ + + + + 1 + + + +
+ + +
+
+23 11
+
++
1+ +1 ++
++
++ + +
+22 + +++ + ++
1
2
21 ++ +
+
++
++ 1+ +
Species group L +
+ + + +
Eragrostis racemosa Helichrysllm pilosellllm Dicoma anomala Alloteropsis semialata Oxalis obliquifolia LOlldetia simplex
+
1
22 2 +++ + + ++ + +
1+ + + +
+ +
+
Tristachya lellcothrix Vernonia natalensis Eriosema kraussiana watsonia densiflora Cyanotis speciosa Hypoxis kraussiana
+
31 ++ ++ + + + + + 1 +
++
4 21 + ++ + +
2+
Species group G 4423 3123 + ++ ++ + +
3 2 + + + + +
1331 12+1 ++ + + + + + + + +
Species group H
+
1
11
+ + 1
+
++ 1++ +
2 + +
11
2
1111
3 + +
1221 +1++ + 1 +++
Species group M
Species group F
Delosperma floribllndllm May tenus acuminata Eragrostis capensis Myrsine africana Crassula setulosa Dihetropogon amplectens Elionurus muticus Rabdosiella calycina Rhlls discolor Senecio crepidifolills Berkheya setifera senecio conrathii Silene bllrchellii Erica cerinthoides Podocarplls latifolills Aleetra orobanchoides Berkheya radllla Diospyros whyteana Eragrostis cassia Helichrysllm appendiclllatllm Helichrysllm spiralepis Helichrysum sutherlandii Lotononis calycina Protea caffra Sebaea grandis Zalusianskia spathacea Senecio ~y~nensis Digitaria tricholaenoides Acalypha pllnctata An~hospermllm herbacellm Hyparrhenia hirta Rhlls dentata Leonotis leonurus Schi'stostephillm crataegifolium
2 2
11
22 23
Species group K
Species group E
Themeda triandra Monocymbium ceresiiforme Helichrysllm oreophilllm Senecio venosusHypoxis rigidula Sopubia cana Pteridillm aquilinillm
2.1
0120 9439 7626 2
COMMUNITIES
Panicum natalense Pearsonia grandifolia Indigofera tristoides
+
species group 0
Heteropogon contortus Acalypha schinzii POlygala uncinata Gnidia·microcephala Xoeleria capensis Ledebouria ovatifolia Oxygonum dregeanum Pentanisia angustifolia Pycrells macranthlls Pygmaeothamnus chamaedendrum
2 1 6
Species group J
+
Gnidia kraussiana Hesperantha baurii Habenaria dives Gnidia caffra
Diheteropogon filifolills Helichrysllm miconiifolium Helichrysum aureonitens Commelina africana Helichrysum adenocarpum Helichrysum aClltatllm
0000 9999 1345
Aristida jllnciformis Sporobollls centrifllgus Craterocapsa tarsodes
species group C
Scilla nervosa Syncolostemon concinnus Ipomoea crassipes Lactllca capensis Indigofera hilaris Aristea angolensis
a 9 2
3
Species group A
Andropogon schirensis Haplocarpa scaposa Selago compacta Crassula vaginata
RELEVES
Species group I
COMMUNITIES
Aristida congesta Vernonia galpinii Senecio erubescens osteospermum caulescens
Table 1 Continued
+ + R+ ++ ++ ++ ++ ++ 1+ ++ ++ ++ ++ ++ 1 R + + + + + + + + + + + + 1 + + + + + +
2 + + 1
++++ +2+2 + ++
1
+
3323 + 2+ + + + +
31 ++ 1+ +1 ++ +
++ +++ + 1+ ++ +
1+ + + + + ++
+ +
2.3 The Tristachya leucothrix - Diheteropogon filifolius Low Closed Grassland on shallow soils. 2.4 The Themeda triandra - Heteropogon contortus Low Closed Grassland. 3. The Aristida junciformis subsp. junciformis - Sporobolus centrifugus Grassland on sandstone. 3.1 The Aristida junciformis subsp. junciformis - Delosperma floribundum Low Sparse Shrubland on sandstone cliff-edges. 3.2 The Aristida junciformis subsp. junciformis - Helichrysum chionosphaerum Low Closed Grassland on sandstone outcrops. Description of the communities
1. The Tristachya leucothrix - Aristida congesta subsp. congesta Low Closed Grassland on flat sandstone outcrops The one releve representing this community was compiled on a flat sandstone outcrop on the edge of a small plateau in the Normandien Pass, at an altitude of approximately 2000m. Diagnostic species for this community are the forbs Senecio erubescens var. dichotomus, Vernonia galpinii and Osteospermum caulescens, as well as the grass Aristida congesta subsp. congesta (species group A, Table 1). The dominant grasses are Andropogon schirensis and Tristachya leucothrix. Other prominent grasses are Aristida congesta subsp. congesta, Diheteropogon filifolius, Eragrostis racemosa and Alloteropsis semialata: The very rocky habitat is probably the reason for the absence of Themeda
120
triandra and for the poorness of species. The occurrence of Andropogon schirensis in such a rocky habitat is quite common. The diagnostic grass Aristida congesta subsp. congesta is an indicator of hard and loamy soils or rocky areas and/or disturbed ground (Gibbs-Russell et al. 1990). 2. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland This community can be regarded as the (fire) climax grassland (Tainton 1981) in the Ad land type. It occurs on deep soils as well as rocky areas and shallow soils. The difference in habitat between this community and community 3 is that the latter occurs on almost solid sandstone rocks. The diagnostic species of this community are given in species group G (Table 1), which include the dominant grasses Themeda triandra and Monocymbium ceresiiforme, as well as the forbs Helichrysum oreophilum, Senecio venosus, Hypoxis rigidula and Sopubia cana, and the bracken fern Pteridium aquilinium. Themeda triandra and Monocymbium ceresiiforme are also the dominant grasses, but Eragrostis racemosa and Tristachya leucothrix are locally abundant. The low height of Themeda triandra and M onocymbium ceresiiforme of 500 mm or less at this altitude (approximately 2000 m) is a characteristic feature.
2.1 The Themeda triandra - Scilla nervosa Low Closed Grassland on deep, non-rocky soils Although the amount of superficial rocks in this community is low, soil depth varies, but generally this community occurs on deep soils (>500 mm), whereas community 2.2 occurs on shallow, sandy Mispah soils. All releves representing this community were compiled on top of Normandien Pass, on gentle north-east-facing slopes on the plateau and on crests. The Clovelly soil form and occasionally the Mispah soil form, were identified in this subcommunity. The diagnostic species for this community appear under species group C (Table 1) and include the forbs Scilla nervosa, Syncolostemon concinnus, Ipomoea crassipes, Lactuca capensis, Indigofera hilaris and Aristea angolensis subsp. angolensis. The dominant grasses are Themeda triandra, Monocymbium ceresiiforme and Andropogon schirensis. Other abundant species are the grass Tristachya leucothrix and the forb Eriosema kraussiana.
2.2 The Themeda triandra - Gnidia kraussiana Low Closed Grassland on shallow, sandy Mispah soils This community is represented by only one rei eve, which was compiled on the remote and inaccessable plateau in the Ncandu Forest Reserve [between Muller's Pass and Normandien Pass (Figure 1)], on a very gentle south-facing slope. The underlying rock is sandstone, which gave rise to a shallow, sandy Mispah soil. The diagnostic species in species group D (Table 1) include the forbs Gnidia kraussiana and Gnidia caffra, the geophyte Hesperantha baurii, as well as the rare orchid, Habenaria dives.
S.-Afr.Tydskr.Plantk.• 1993.59(2)
Themeda triandra, Andropogon schirensis. Eragrostis racemosa and Monocymbium ceresiiforme are the dominant grasses.
2.3 The Tristachya leucothrix - Diheteropogon filifolius Low Closed Grassland on shallow soils Few superficial rocks were observed in the sample plots of this community. The soils are, however, predominantly shallow and of the Mispah soil form. The releves were compiled on the plateau on top of Normandien Pass on southeast-facing slopes. The diagnostic species are given in species group E (Table 1) and include the grass Diheteropogonfilifolius and the forbs Helichrysum miconiifolium. Helichrysum aureonitens, Helichrysum adenocarpum and Commelina africana. Helichrysum aureonitens and Commelina africana indicate poor drainage on the shallow soils. The dominant species are the grasses Themeda triandra, Monocymbium ceresiiforme and Dihetropogonfilifolius. An obvious difference with Community 2.1 is the low presence of Andropogon schirensis and the prominence of Diheteropogonfilifolius in this community. 2.4 The Themeda triandra - Heteropogon contortus Low Closed Grassland on deep soils The releves representing this community were compiled in the Ncandu Forest Reserve on deep soils on gentle slopes on the plateau. The soil was identified as the Clovelly soil form. The difference in soil depth probably causes the difference in diagnostic species as given in species group F (Table 1). The grass Heteropogon contortus and the forbs Acalypha schinzii and Polygala uncinata are the diagnostic species shared by both releves. Other diagnostic species include the grass Koeleria capensis and the forbs Gnidia microcephala, Ledebouria ovatifolia, Oxygonum dregeanum subsp. lanceolatum, Pentanisia angustifolia and Pygmaeothamnus chamaedendrum, as well as the sedge Pycreus macranthus. The dominant species are the grasses Themeda triandra, Tristachya leucothrix and Heteropogon contortus.
3. The Aristida junciformis subsp. junciformis Sporobolus centrifugus Grassland on sandstone The diagnostic species (species group J, Table 1) include the grasses Aristida junciformis subsp. junciformis and Sporobolus centrifugus, as well as the forb Craterocapsa tarsodes. Aristida junciformis subsp. junciformis (Ngongoni) is the dominant grass and indicates rocky or shallow soils or disturbance (Gibbs Russell et al. 1990). Edwards (1967) stated that an increase of Aristida junciformis is a result of intensive utilization of grassland. In this community though, the rockiness and shallow soils are reasons for the abundance of the species. The habitat in the two subcommunities of this community is very similar, namely almost solid sandstone or small cliffs on edges of valley sides. Community 3.1 represents vegetation on the edge of the plateau above the Ncandu River Valley as well as on the cliff edges of the Union Butte,
S.Afr.I.Bot., 1993, 59(2)
while Community 3.2 represents vegetation on the Free State Plateau, on the edge of the plateau above the Klip River Valley. Stunted shrubs and trees occur in Community 3.1, but are absent in Community 3.2.
3.1 The Aristida junciformis subsp. junciformis Delosperma jloribundum Low Sparse Shrublan~ on sandstone clifT-edges The releves representing this community were all compiled in the Ncandu Forest Reserve, on almost solid sandstone cliff-edges on the edge of the plateau, bordering the deep valley sides through which the Ncandu River flows. The valley sides belong to the Fa land type and the plateau to the Ad land type (Figure 2). Vegetation occurs in cracks and soil pockets in the rocks. Diagnostic species (species group H, Table 1) which occur in at least two of the three releves, are the grasses Eragrostis capensis, Diheteropogon amplectens and Elionurus muticus, the forbs Delosperma floribundum, Crassula setulosa var. setulosa, Rhabdosiella calycina, Senecio erubescens var. crepidifolius, Berkheya setifera, Senecio conrathii and Silene burchellii, and the woody Rhus discolor. Diagnostic trees and shrubs with stunted growth are May tenus acuminata and Myrsine africana. The most abundant grass is Aristida junciformis subsp. junciformis due to the shallow soils. Other grass species are Sporobolus centrifugus and Eragrostis racemosa.
3.2 The Aristida junciformis subsp. junciformis Helichrysum chionosphaerum Low Closed Grassland on sandstone outcrops The releves representing this community were compiled on the Free State Plateau, on top of sandstone cliffs or outcrops bordering valley sides. The valley sides belong to the Ca land type and the plateau to the Ad land type (Figure 2). The vegetation cover in this extremely rocky habitat is sparse and soil, where present, is shallow. Diagnostic species (species group J, Table 1) are the forbs Helichrysum chionosphaerum, Gazania krebsiana , Monsonia attenuata, Scabiosa columbaria. Crassula pellucida. subsp. setilobus. Senecio Euryops transvaalensis rhomboideus. Gladiolus permeabilis and Delosperma gracile. Diagnostic grass species are Microchloa caffra. Andropogon appendiculatus and Eragrostis plana. The dominant grass is Aristida junciformis subsp. junciformis; other grasses of importance are Tristachya leucothrix and Sporobolus centrifugus.
Concluding remarks This study is a successful application of refining the results of a TwINSPAN classification with Braun-Blanquet procedures. The three major plant communities were ecologically interpretable and all relate to specific environmental conditions. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland on deep as well as shallow soils is regarded as the (fire) climax grassland community in this land type. The two other communities occur on extremely rocky habitats.
121
The value of this study lies in its potential as basis for formulating management programmes. Management programmes should be based on the principle that each of the identified plant communities exists as a unique ecological and management unit. This applies not only to regional land-use planning and management on farm level, but the unique range of plant community types in this region has important implications regarding conservation. It may serve as a tool in selecting future areas for conservation. The results of this phytosociological study should be incorporated with those of the Bb, Bd, Ea, Ac, Fa and Ca land types (Smit 1992), in order to achieve an hierarchical syntaxonomy of the vegetation of the north-western part of Natal and the adjacent part of the Orange Free State.
References ACOCKS, J.P.H. 1953. Veld types of South Africa, 1st. edn. Mem. bot. Surv. S. Afr. No. 40: 1 - 128. ACOCKS, J.P.H. 1988. Veld types of South Africa, 3rd. edn. Mem . bot. Surv. S. Afr. No. 57: 1 - 146. BEHR, C.M.J. & BREDENKAMP, G.J . 1988. A phytosociological classification of the Witwatersrand National Botanic Garden. S. Afr. 1. Bot. 54: 525 - 533. BREDENKAMP, G.I. 1975. 'n Plantekologiese studie van die Suikerbosrandnatuurreservaat. M.Sc. Thesis, University of Pretoria, Pretoria. BREDENKAMP, G.I. 1982. 'n Plantekologiese studie van die Manyeleti Wildtuin. D.Sc. Thesis, University of Pretoria, Pretoria. EDWARDS, D. 1967. A plant ecological survey of the Tugela Basin. Mem. bot. Surv. S. Afr. No. 35: 1 - 285. EDWARDS, D. 1983. A broad-scale classification of vegetation for practical purposes. Bothalia 14: 705 - 712. GIBBS RUSSELL, G.E., REID, C., VAN ROOYEN, J. & SMOOK, L. 1985. List of species of southern African plants, 2nd edn., Part 1. Mem . bot. Surv. S. Afr. No. 51: 1 - 152. GIBBS RUSSELL, G.E., WELMAN, W.G., RETIEF, E., IMMELMAN, K.L., GERMISHUIZEN, G., PIENAAR, B.J., VAN WYK, M., NICHOLAS, A., DE WET, C., MOGFORD, J.C. & MULVENNA, J . 1987. List of species of Southern African plants, 2nd edn., Part 2. Mem. bot. Surv. S. Afr. No. 56: 1 - 270. GIBBS RUSSELL, G.E., WATSON, L., KOEKEMOER, M., SMOOK, L., BARKER, N.P., ANDERSON, H.M. & DALLWITZ, M.I. 1990. Grasses of Southern Africa. Mem. bot. Surv. S. Afr. No. 58: 1 - 437. HILL, M.O. 1979. TWINSPAN - a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of individuals and attributes. Cornell, New York. LAND TYPE SURVEY STAFF. 1984. Land types of the maps 2522 Bray, 2622 Morokweng, 2524 Mafeking, 2624 Vryburg. Mem. agric. nat. Resources S. Afr. No. 1: 1 - 281. LAND TYPE SURVEY STAFF. 1990. Geological, climatological & soil analyses data for the 2728 Frankfort land type map. Computer print-out. Soil and Irrigation Research Institute, Pretoria. MACVICAR, C.N., LOXTON, R.F., LAMBRECHTS, J.J.N., LE ROUX, J., DE VILUERS, J .M., VERSTER, E., MERRYWEATHER, P.R., VAN ROOYEN, T.H. & HARMSE, H.I. von M. 1977. Soil classification, a binomial system for South Africa. Department of Agricultural Technical Services, Pretoria. MENTIS, M.T. & HUNTLEY, B.I. 1982. A description of the Grassland Biome Project. Cooperative Scientific Programme,
122 CSIR Rep. No. 62. Graphic Arts Division of the CSIR, Pretoria. MUELLER-DOMBOIS, D. & ELLENBERG, H. 1974. Aims and methods of vegetation ecology. Wiley, New York. PHILLIPS , J. 1973. The agricultural and related development of the Tugela Basin and its influent surrounds. A study in Subtropical Africa. Natal Town and Regional Planning Report, Vol. 19. Town and Regional Planning Commission, Natal. SCHEEPERS, T.C. 1986. Grassland Biome Project: Proceedings of the workshop on classification and mapping. Ecosystems Programmes Occassional Rep. Ser. No. 16, CSIR, Pretoria. SCHULZE, R.E. 1982. Agrohydrology and -Climatology of Natal. Agricultural Catchments Research Unit, Rep. No. 14. Department of Agricultural Engineering, University of Natal, Pietermaritzburg, South Africa. SMIT, C.M. 1992. Phytosociology of the Newcastle Memel Chelmsford Dam area. M.Sc. Thesis, University of Pretoria, Pretoria. SMIT, C.M., BREDENKAMP, GJ. & VAN ROOYEN, N. 1992. Phytosociology of the B land type in the Newcastle - Memel Chelmsford Dam area. S. Afr. 1. Bot. 58: 363 - 373. SMIT, C.M. , BREDENKAMP, GJ. & VAN ROOYEN, N. 1993a. Woodland plant communities of the Fa land type in the Newcastle - Memel - Chelmsford Dam area. S. Afr. 1. Bot. 59: 14 - 20.
S.-Afr.Tydskr.Plantk., 1993, 59(2) SMIT, C.M, BREDENKAMP, GJ. & VAN ROOYEN, N. 1993b. Phytosociology of the Ac land type in the foothills of the Low Drakensberg, north-western Natal. S. Afr. 1. Bot. 59: 203 - 214. SOIL AND IRRIGATION RESEARCH INSTITUTE. 1984. Land Type Map: 2728 Frankfort. Government Printer, Pretoria. TAINTON, N.M. 1981. Veld and pasture management in South Africa. Shuter & Shooter, Pietermaritzburg; in assosiation with the University of Natal, Pietermaritzburg. VAN DER EYK, JJ., MACVICAR, C.N. & DE VILLIERS, J.M. 1969. Soils of the Tugela Basin: a study in subtropical Africa. Natal Town and Regional Planning Reports, Volume 15. Town and Regional Planning Commission, Natal. VISSER, H.N. & BISHOPP, D.W. 1976. The geology of the Newcastle and Dundee areas and a detailed description of the Klip River Coalfield of Northern Natal: Explanation of the sheets 2729D (Newcastle), 2730C (Utrecht), 2829B (Elandslaagte) and 2830A (Dundee). Geological Survey, Department of Mines, South Africa. WEATHER BUREAU. 1990. Climatological data for 1987 - 1990 for the Newcastle Weather station. Computer printout, Weather Bureau, Pretoria. WESTHOFF, V. & VAN DER MAAREL, E. 1978. The BraunBlanquet Approach. In: Classification of Plant Communities, ed. R.H. Whittaker, ch. 20. Junk, The Hague.
116
Plant communities of the Ad land type in the Newcastle - Memel - Chelmsford Dam area C.M. Smit,* G.J. Bredenkamp and N. van Rooyen Department of Botany, University of Pretoria, Pretoria, 0002 Republic of South Africa Received 12 August 1992; revised 27 October 1992
The Ad land type in the Newcastle - Memel - Chelmsford Dam area comprises areas of the plateau of the Low Drakensberg range and is associated with the Fa and Ca land types. Seventeen releves were compiled in this land type, which were firstly numerically classified (TwINsPAN) and the results of this classification were further refined by Braun-Blanquet procedures. Three major plant communities and seven subcommunities were recognized. The Themeda triandra - Monocymbium ceresiiforme grassland can be regarded as the most extensive vegetation type in this land type . A description, ecological interpretation and hierarchical classification of the plant communities are presented. Die Ad-Iandtipe van die Newcastle - Memel - Chelmsforddamgebied maak dee I uit van die plato van die Lae Drakensbergreeks en is geassosieer met die Fa- en Ca-Iandtipes. Sewentien releves is in hierdie landtipe saamgestel wat eers numeries geklassifiseer (TWINSPAN) is. Die resultate van hierdie klassifikasie is verder met behulp van Braun-Blanquetprosedures verfyn. Drie hoofgemeenskappe en sewe onderverdelings is ge·identifiseer, waarvan die Themeda triandra - Monocymbium ceresiiforme-grasveld as die hoofplantegroeitipe van die landtipe beskou kan word. 'n Hierargiese klassifikasie, beskrywing en ekologiese interpretasie van die plantgemeenskappe word aangebied.
Keywords: Ad land type, Braun-Blanquet procedures, numerical classification, ecological interpretation, grassland . • To whom correspondence should be addressed.
Introduction Mentis and Huntley (1982) and Scheepers (1986) stated the necessity to identify, describe and classify the major vegetation types within the Grassland Biome of South Africa. Besides being able to make a contribution to grassland veld management programmes, the Grassland Biome Project aims at producing a vegetation map on a 1:250000 scale (Scheepers 1986). Land types, as identified by the Land Type Survey Staff (1984, 1990), are used as stratification units. Parameters distinguishing one land type from another are terrain morphology, soil pattern/types and climate (Land Type Survey Staff 1984). The phytosociological classification of the vegetation of the Ad land type of the Newcastle - Memel - Chelmsford Dam area forms part of the Grassland Biome Project. According to Acocks's (1953, 1988) map and description, this area is classified as 'Highland Sourveld' (44a). The closest description of Edwards (1967) which conforms to the vegetation encountered in the Ad land type within the study area, is the 'Themeda - Trachypogon Highlands Grassland', especially the 'Low Drakensberg and Biggarsberg Faciation'. As these studies are of a large scale and done a considerable length of time ago, the need arose to do a more comprehensive phytosociological study of this particular area. The Ad land type in the study area is almost inaccessible, and is therefore totally undeveloped. As far as agriculture is concerned, it is only used for grazing; no ploughed fields were observed.
The study area The study area is situated between 27°33' and 28°00' S
latitude and 29°33' and 300 00'E longitude, in the Grassland Biome of north-western Natal, South Africa. The Ad land type in the study area occurs at an altitude of 1800 2000 m and its position is indicated in Figure 1. A detailed description of the physical environment was given by Smit (1992). Soils Most of the soils in this land type are shallow and of the Mispah soil form, although the Clovelly soil form has been recorded in a few instances. The soil classification nomenclature conforms to that of MacVicar et al. (1977). According to the Land Type Survey Staff (1984), the 'A' map units refer to yellow and red soils without water tables and to land which does not qualify as a plinthic catena. In the Ad land type in particular, yellow, dystrophic and/or mesotrophic soils occupy a larger area than high base status red-yellow apedal soils. Topography
The Ad land type in the study area consists mainly of the Free State Plateau (Van der Eyck et al. 1969), topping the Low Drakensberg range. To the east the Ad land type is in close association with the Fa land type [where rocky soils with Glenrosa or Mispah soil forms predominate, with lime absent in the entire landscape (Land Type Survey Staff 1984)], which forms the escarpment of the Low Drakensberg. To the west it is in close association with the Ca land type [where a plinthic catena, with duplex and/or margalithic soils, predominates (Land Type Survey Staff 1984)], which consists mainly of a plateau with incised valleys of
S.AfrJ.Bot., 1993, 59(2)
117
o
SCALE:
~.
5
10
15
20 KM
_ _..:L..'- - - - - - , ' - - - - - - ' - '- - - "
.... . ............ []J . .
Bb land type
Fa land type
.............. .. ......... [ill[] ................ .............. ..... ...... .
Ea land type
Ad land type
tr@n~nd
Ac land type
a . . . . . . . . ..
..
.. .
. ..
.......
........... e . . .. '
..
Ca land type Drainage lines
Immllllll:l:~ll:lli
Roads Bd land type --~
...
Natal/OFS border
I/ItI
Ncandu Forest Reserve
<.
Marshland
Zeekoeivlei
Border of study area
•
Approx. position of section A (Figure 2)
Figure 1 Position of the Bb, Bel, Fa, Ea, Ac, Ad and Ca land types in the Newcastle - Memel - Chelmsford Dam area (adapted from 1:250000 Land Type Series, 2728 Frankfort, Soil and Irrigation Research Institute, 1984).
streams draining into the Vaal River system (Figure 1) . The topography on the plateau is not all very gentle, but is dotted with hills and ridges, e.g. the Union Butte, one of the high-
est points in the study area, The terrain type of the Ad land type is classified as A3 (Land Type Survey Staff 1990). 'A' means that more than
S.-Afr.Tydskr.Plantk.• 1993.59(2)
118
80% of the area has slopes less than 8% and '3' indicates local relief, which in this case means that the difference between the highest and lowest pQints in the landscape varies between 90 and 150 m (Land Type Survey Staff 1984). Geology The geology of the entire study area was discussed by Smit (1992). The Middle Beaufort Stage (Visser & Bishopp 1976) is represented in the Ad land type in the study area and consists mainly of sandstone and grit, with small areas of dolerite. At Normandien Pass (Figure 1) are carbonaceous and iron-rich shale partings. Climate According to the description of the climate of the entire study area by Smit (1992), the Ad land type belongs to the area referred to as 'Mountain Regions'. The climate of this area conforms to Phillips's (1973) Bioclimatic Group 4, in which the mean annual precipitation is 1120 mm and the mean annual temperature 14°C. The highest mean daily maximum temperature of 24°C was recorded in January and the lowest mean daily minimum temperature of O°C was recorded in July (Schulze 1982; Weather Bureau 1990). Methods Over the entire study area, releves were compiled in 282 stratified random sample plots. Stratification was firstly based on land type. The number of sample plots allocated to the various land types recognized in the area, was determined pro rata and on an area basis. In this way 17 sample plots were placed in the Ad land type. Stratification within the land type was defined on terrain units. The small number of releves can be ascribed to the inaccessability of the area and to the fact that the Ad land type comprises only approximately 8% of the study area. For grassland vegetation, plot size was 10 X 10 m (Bredenkamp 1975), and for woodland 10 X 20 m (Bredenkamp 1982). Contour profiles were drawn from 1:50 000 topocadastral maps (Figure 2), in order to illustrate the terrain types of the area. Five terrain units were recognized on which stratification was based, namely 1 (crest), 2 (scarp), 3 (midslope), 4 (foots lope) and 5 (valley bottom or flood plain). The single- as well as the multi-phase terrain types were recognized (Land Type Survey Staff 1984). The Braun-Blanquet cover-abundance scale (MuellerDombois & Ellenberg 1974) was used to record the total floristic composition in each sample plot. Habitat
information such as geology, topography, topographic position, soil form and series, rockiness, rock size and vegetation structure were also recorded. Vegetation structure was classified according to Edwards's (1983) system and the predominant structural classification of the recognized plant communities is used in the name of each plant community. Taxa names conform to those of Gibbs Russell et al. (1985, 1987, 1990). The first step in classification of the floristic data was to apply Two-way Indicator Species Analysis (TwINS PAN) (Hill 1979) to the data, which resulted in a first approximation of the vegetation types of the area. This classification was then further refined with Braun-Blanquet procedures (Westhoff & Van der Maarel 1978; Behr & Bredenkamp 1988). The final results are presented in a phytosociological table (Table 1). Results Classification The vegetation of the Ad land type is mainly grassland of which the Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland is the most extensive grassland community, not only in the Ad land type, but also in the Bb (Smit et al. 1992), Fa (Smit et al. 1993a) and Ac (Smit et al. 1993b) land types. Each land type though, reveals its own subcommunities and variants of this broad Themeda triandra - Monorymbium ceresiiforme grassland. Subcommunities of this grassland are associated with soil depth and rockiness. Three other communities on extremely rocky habitats were also recognized. Woody vegetation is sparse and when present, stunted. These grasslands are known as 'sourveld' or fire climax grasslands, which means that the grassland stage is maintained by the regular occurrence of fire (Tainton 1981). It seems as though altitude and exposure may be causal factors for the sparse occurrence and stunted growth of trees and shrubs and not solely fire as management tool. The communities were hierarchically classified as follows: 1. The Tristachya leucothrix - Aristida congesta subsp.
congesta Low Closed Grassland on flat sandstone outcrops. 2. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland 2.1 The Themeda triandra - Scilla nervosa Low Closed Grassland on deep, non-rocky soils. 2.2 The Themeda triandra - Gnidia kraussiana Low Closed Grassland on shallow, sandy Mispah soils.
A
:§ 1905
Ad
I
27"53'36·S
I
I _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .l_ 29·41 10u E
Figure 2 Contour profiles of the Ad land type at 2r53'36"S latitude. showing its relation to the Ca and Fa land types (South Africa 1:50000 sheet 2729 Mont Pelaan).
119
S.AfrJ.Bot., 1993, 59(2)
Table 1 A phytosociological table of plant communities in the Ad land type in the Newcastle - Memel - Chelmsford Dam area a
RELEVES
0000 9999 1345
9 2
2 1 6
0120 9439 7626
11 22 23
122 233 101
2
11 44 37
1
2.1
2 ·2
2.3
2. 4
3. 1
3. 2
1 + + +
++
3 + +
3323 ++ + + + +
+
+
Species group B 3
+1 + + ++
+
+ +
+++ ++
+
+
+
+ +
122 233 101
1
11 44 37 3
2.3
2. 4
3.1
3. 2
Helichrysum chionosphaerum Gazania krebsiana Monsonia attenuata Scabiosa col umbari a Crassllla pellllcida Ellryops transvaalensis Senecio rhomboidells Microchloa caffra Andropogon appendiclllatus Eragrostis plana Gladiollls permeabilis Delosperma gracile
+1 ++ ++ + + + + 1 + + + +
+ + +
+
+23 11
+
++
1+ +1 ++
++
++ + +
+22 + +++ + ++
1
2
21 ++ +
+
++
++ 1+ +
Species group L +
+ + + +
Eragrostis racemosa Helichrysllm pilosellllm Dicoma anomala Alloteropsis semialata Oxalis obliquifolia LOlldetia simplex
+
1
22 2 +++ + + ++ + +
1+ + + +
+ +
+
Tristachya lellcothrix Vernonia natalensis Eriosema kraussiana watsonia densiflora Cyanotis speciosa Hypoxis kraussiana
+
31 ++ ++ + + + + + 1 +
++
4 21 + ++ + +
2+
Species group G 4423 3123 + ++ ++ + +
3 2 + + + + +
1331 12+1 ++ + + + + + + + +
Species group H
+
1
11
+ + 1
+
++ 1++ +
2 + +
11
2
1111
3 + +
1221 +1++ + 1 +++
Species group M
Species group F
Delosperma floribllndllm May tenus acuminata Eragrostis capensis Myrsine africana Crassula setulosa Dihetropogon amplectens Elionurus muticus Rabdosiella calycina Rhlls discolor Senecio crepidifolills Berkheya setifera senecio conrathii Silene bllrchellii Erica cerinthoides Podocarplls latifolills Aleetra orobanchoides Berkheya radllla Diospyros whyteana Eragrostis cassia Helichrysllm appendiclllatllm Helichrysllm spiralepis Helichrysum sutherlandii Lotononis calycina Protea caffra Sebaea grandis Zalusianskia spathacea Senecio ~y~nensis Digitaria tricholaenoides Acalypha pllnctata An~hospermllm herbacellm Hyparrhenia hirta Rhlls dentata Leonotis leonurus Schi'stostephillm crataegifolium
2 2
11
22 23
Species group K
Species group E
Themeda triandra Monocymbium ceresiiforme Helichrysllm oreophilllm Senecio venosusHypoxis rigidula Sopubia cana Pteridillm aquilinillm
2.1
0120 9439 7626 2
COMMUNITIES
Panicum natalense Pearsonia grandifolia Indigofera tristoides
+
species group 0
Heteropogon contortus Acalypha schinzii POlygala uncinata Gnidia·microcephala Xoeleria capensis Ledebouria ovatifolia Oxygonum dregeanum Pentanisia angustifolia Pycrells macranthlls Pygmaeothamnus chamaedendrum
2 1 6
Species group J
+
Gnidia kraussiana Hesperantha baurii Habenaria dives Gnidia caffra
Diheteropogon filifolills Helichrysllm miconiifolium Helichrysum aureonitens Commelina africana Helichrysum adenocarpum Helichrysum aClltatllm
0000 9999 1345
Aristida jllnciformis Sporobollls centrifllgus Craterocapsa tarsodes
species group C
Scilla nervosa Syncolostemon concinnus Ipomoea crassipes Lactllca capensis Indigofera hilaris Aristea angolensis
a 9 2
3
Species group A
Andropogon schirensis Haplocarpa scaposa Selago compacta Crassula vaginata
RELEVES
Species group I
COMMUNITIES
Aristida congesta Vernonia galpinii Senecio erubescens osteospermum caulescens
Table 1 Continued
+ + R+ ++ ++ ++ ++ ++ 1+ ++ ++ ++ ++ ++ 1 R + + + + + + + + + + + + 1 + + + + + +
2 + + 1
++++ +2+2 + ++
1
+
3323 + 2+ + + + +
31 ++ 1+ +1 ++ +
++ +++ + 1+ ++ +
1+ + + + + ++
+ +
2.3 The Tristachya leucothrix - Diheteropogon filifolius Low Closed Grassland on shallow soils. 2.4 The Themeda triandra - Heteropogon contortus Low Closed Grassland. 3. The Aristida junciformis subsp. junciformis - Sporobolus centrifugus Grassland on sandstone. 3.1 The Aristida junciformis subsp. junciformis - Delosperma floribundum Low Sparse Shrubland on sandstone cliff-edges. 3.2 The Aristida junciformis subsp. junciformis - Helichrysum chionosphaerum Low Closed Grassland on sandstone outcrops. Description of the communities
1. The Tristachya leucothrix - Aristida congesta subsp. congesta Low Closed Grassland on flat sandstone outcrops The one releve representing this community was compiled on a flat sandstone outcrop on the edge of a small plateau in the Normandien Pass, at an altitude of approximately 2000m. Diagnostic species for this community are the forbs Senecio erubescens var. dichotomus, Vernonia galpinii and Osteospermum caulescens, as well as the grass Aristida congesta subsp. congesta (species group A, Table 1). The dominant grasses are Andropogon schirensis and Tristachya leucothrix. Other prominent grasses are Aristida congesta subsp. congesta, Diheteropogon filifolius, Eragrostis racemosa and Alloteropsis semialata: The very rocky habitat is probably the reason for the absence of Themeda
120
triandra and for the poorness of species. The occurrence of Andropogon schirensis in such a rocky habitat is quite common. The diagnostic grass Aristida congesta subsp. congesta is an indicator of hard and loamy soils or rocky areas and/or disturbed ground (Gibbs-Russell et al. 1990). 2. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland This community can be regarded as the (fire) climax grassland (Tainton 1981) in the Ad land type. It occurs on deep soils as well as rocky areas and shallow soils. The difference in habitat between this community and community 3 is that the latter occurs on almost solid sandstone rocks. The diagnostic species of this community are given in species group G (Table 1), which include the dominant grasses Themeda triandra and Monocymbium ceresiiforme, as well as the forbs Helichrysum oreophilum, Senecio venosus, Hypoxis rigidula and Sopubia cana, and the bracken fern Pteridium aquilinium. Themeda triandra and Monocymbium ceresiiforme are also the dominant grasses, but Eragrostis racemosa and Tristachya leucothrix are locally abundant. The low height of Themeda triandra and M onocymbium ceresiiforme of 500 mm or less at this altitude (approximately 2000 m) is a characteristic feature.
2.1 The Themeda triandra - Scilla nervosa Low Closed Grassland on deep, non-rocky soils Although the amount of superficial rocks in this community is low, soil depth varies, but generally this community occurs on deep soils (>500 mm), whereas community 2.2 occurs on shallow, sandy Mispah soils. All releves representing this community were compiled on top of Normandien Pass, on gentle north-east-facing slopes on the plateau and on crests. The Clovelly soil form and occasionally the Mispah soil form, were identified in this subcommunity. The diagnostic species for this community appear under species group C (Table 1) and include the forbs Scilla nervosa, Syncolostemon concinnus, Ipomoea crassipes, Lactuca capensis, Indigofera hilaris and Aristea angolensis subsp. angolensis. The dominant grasses are Themeda triandra, Monocymbium ceresiiforme and Andropogon schirensis. Other abundant species are the grass Tristachya leucothrix and the forb Eriosema kraussiana.
2.2 The Themeda triandra - Gnidia kraussiana Low Closed Grassland on shallow, sandy Mispah soils This community is represented by only one rei eve, which was compiled on the remote and inaccessable plateau in the Ncandu Forest Reserve [between Muller's Pass and Normandien Pass (Figure 1)], on a very gentle south-facing slope. The underlying rock is sandstone, which gave rise to a shallow, sandy Mispah soil. The diagnostic species in species group D (Table 1) include the forbs Gnidia kraussiana and Gnidia caffra, the geophyte Hesperantha baurii, as well as the rare orchid, Habenaria dives.
S.-Afr.Tydskr.Plantk.• 1993.59(2)
Themeda triandra, Andropogon schirensis. Eragrostis racemosa and Monocymbium ceresiiforme are the dominant grasses.
2.3 The Tristachya leucothrix - Diheteropogon filifolius Low Closed Grassland on shallow soils Few superficial rocks were observed in the sample plots of this community. The soils are, however, predominantly shallow and of the Mispah soil form. The releves were compiled on the plateau on top of Normandien Pass on southeast-facing slopes. The diagnostic species are given in species group E (Table 1) and include the grass Diheteropogonfilifolius and the forbs Helichrysum miconiifolium. Helichrysum aureonitens, Helichrysum adenocarpum and Commelina africana. Helichrysum aureonitens and Commelina africana indicate poor drainage on the shallow soils. The dominant species are the grasses Themeda triandra, Monocymbium ceresiiforme and Dihetropogonfilifolius. An obvious difference with Community 2.1 is the low presence of Andropogon schirensis and the prominence of Diheteropogonfilifolius in this community. 2.4 The Themeda triandra - Heteropogon contortus Low Closed Grassland on deep soils The releves representing this community were compiled in the Ncandu Forest Reserve on deep soils on gentle slopes on the plateau. The soil was identified as the Clovelly soil form. The difference in soil depth probably causes the difference in diagnostic species as given in species group F (Table 1). The grass Heteropogon contortus and the forbs Acalypha schinzii and Polygala uncinata are the diagnostic species shared by both releves. Other diagnostic species include the grass Koeleria capensis and the forbs Gnidia microcephala, Ledebouria ovatifolia, Oxygonum dregeanum subsp. lanceolatum, Pentanisia angustifolia and Pygmaeothamnus chamaedendrum, as well as the sedge Pycreus macranthus. The dominant species are the grasses Themeda triandra, Tristachya leucothrix and Heteropogon contortus.
3. The Aristida junciformis subsp. junciformis Sporobolus centrifugus Grassland on sandstone The diagnostic species (species group J, Table 1) include the grasses Aristida junciformis subsp. junciformis and Sporobolus centrifugus, as well as the forb Craterocapsa tarsodes. Aristida junciformis subsp. junciformis (Ngongoni) is the dominant grass and indicates rocky or shallow soils or disturbance (Gibbs Russell et al. 1990). Edwards (1967) stated that an increase of Aristida junciformis is a result of intensive utilization of grassland. In this community though, the rockiness and shallow soils are reasons for the abundance of the species. The habitat in the two subcommunities of this community is very similar, namely almost solid sandstone or small cliffs on edges of valley sides. Community 3.1 represents vegetation on the edge of the plateau above the Ncandu River Valley as well as on the cliff edges of the Union Butte,
S.Afr.I.Bot., 1993, 59(2)
while Community 3.2 represents vegetation on the Free State Plateau, on the edge of the plateau above the Klip River Valley. Stunted shrubs and trees occur in Community 3.1, but are absent in Community 3.2.
3.1 The Aristida junciformis subsp. junciformis Delosperma jloribundum Low Sparse Shrublan~ on sandstone clifT-edges The releves representing this community were all compiled in the Ncandu Forest Reserve, on almost solid sandstone cliff-edges on the edge of the plateau, bordering the deep valley sides through which the Ncandu River flows. The valley sides belong to the Fa land type and the plateau to the Ad land type (Figure 2). Vegetation occurs in cracks and soil pockets in the rocks. Diagnostic species (species group H, Table 1) which occur in at least two of the three releves, are the grasses Eragrostis capensis, Diheteropogon amplectens and Elionurus muticus, the forbs Delosperma floribundum, Crassula setulosa var. setulosa, Rhabdosiella calycina, Senecio erubescens var. crepidifolius, Berkheya setifera, Senecio conrathii and Silene burchellii, and the woody Rhus discolor. Diagnostic trees and shrubs with stunted growth are May tenus acuminata and Myrsine africana. The most abundant grass is Aristida junciformis subsp. junciformis due to the shallow soils. Other grass species are Sporobolus centrifugus and Eragrostis racemosa.
3.2 The Aristida junciformis subsp. junciformis Helichrysum chionosphaerum Low Closed Grassland on sandstone outcrops The releves representing this community were compiled on the Free State Plateau, on top of sandstone cliffs or outcrops bordering valley sides. The valley sides belong to the Ca land type and the plateau to the Ad land type (Figure 2). The vegetation cover in this extremely rocky habitat is sparse and soil, where present, is shallow. Diagnostic species (species group J, Table 1) are the forbs Helichrysum chionosphaerum, Gazania krebsiana , Monsonia attenuata, Scabiosa columbaria. Crassula pellucida. subsp. setilobus. Senecio Euryops transvaalensis rhomboideus. Gladiolus permeabilis and Delosperma gracile. Diagnostic grass species are Microchloa caffra. Andropogon appendiculatus and Eragrostis plana. The dominant grass is Aristida junciformis subsp. junciformis; other grasses of importance are Tristachya leucothrix and Sporobolus centrifugus.
Concluding remarks This study is a successful application of refining the results of a TwINSPAN classification with Braun-Blanquet procedures. The three major plant communities were ecologically interpretable and all relate to specific environmental conditions. The Themeda triandra - Monocymbium ceresiiforme Low Closed Grassland on deep as well as shallow soils is regarded as the (fire) climax grassland community in this land type. The two other communities occur on extremely rocky habitats.
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The value of this study lies in its potential as basis for formulating management programmes. Management programmes should be based on the principle that each of the identified plant communities exists as a unique ecological and management unit. This applies not only to regional land-use planning and management on farm level, but the unique range of plant community types in this region has important implications regarding conservation. It may serve as a tool in selecting future areas for conservation. The results of this phytosociological study should be incorporated with those of the Bb, Bd, Ea, Ac, Fa and Ca land types (Smit 1992), in order to achieve an hierarchical syntaxonomy of the vegetation of the north-western part of Natal and the adjacent part of the Orange Free State.
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