South African Journal of Botany 2003, 69(3): 401–409 Copyright © NISC Pty Ltd Printed in — All rights reserved SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254–6299

Vegetation ecology of the pans (playas) of Soetdoring Nature Reserve, Province

BB Janecke*, PJ du Preez and HJT Venter

Department of Plant Sciences, University of the Free State, PO Box 339, 9300, South Africa * Corresponding author, e-mail: [email protected]

Received 3 December 2002, accepted in revised form 22 April 2003

A comparison of the vegetation of two pans (playas) Portulaca oleracea–Cynodon dactylon subcommunity. inside Soetdoring Nature Reserve, a freshwater and a Cynodon transvaalensis is the dominant species in this brackish pan, is presented. These ephemeral pan com- pan. The Open Diplachne Pan is characterised by a munities are also compared to the vegetation of the hot Diplachne fusca–Eragrostis bicolor community with a spring and two permanently inundated earth dams Diplachne fusca subcommunity and an Eragrostis inside the brackish pan’s basin. The vegetation of the bicolor–Diplachne fusca subcommunity associated freshwater communities differs significantly from that with it. Diplachne fusca is dominant in the pan basin. A of the brackish pan itself. The freshwater pan was clas- TWINSPAN classification, refined by Braun-Blanquet sified as a Mixed Grass Pan and the brackish pan as an procedures, revealed five distinct plant communities for Open Diplachne Pan. The Mixed Grass Pan is charac- the pan basins and freshwater areas inside the basin terised by a Cynodon transvaalensis–Gnaphalium decli- collectively. This information is important since very natum community, associated with the following sub- few published analyses are available for pans in the communities: Selago dinteri–Cynodon transvaalensis, Free State Province, as well as in South Africa as a Panicum schinzii–Cynodon transvaalensis and whole.

Introduction

The word wetland is a generic term used to group those fea- ty alters environmental conditions in a way that makes the tures of the landscape, the formation of which has been habitat less favourable for its own survival but more dominated by water, in which processes and characteristics favourable for the development of a different community are largely controlled by water (Maltby 1986), and which are (Maltby 1986). commonly referred to as pans (playas), vleis, floodplains, Pans are widespread in South Africa, but not ubiquitous. marshes, swamps and bogs, as a single type of ecosystem Most of them occur on the arid side of both the 500mm mean (Breen and Begg 1991). annual isohyet and the 1 000mm free surface evaporation Endorheic pans (pans with an inlet but no outlet) are rela- loss isoline (Le Roux 1978, Goudie and Thomas 1985). Pans tively easily defined ecosystems. ‘Pan’ is a South African are distributed throughout various biomes, being especially vernacular term for any large, flat, sediment-filled depres- common in the Grassland, Nama Karoo and Kalahari Biomes sion that collects water after rain (Mepham and Mepham (Allan et al. 1995). Within the arid area there are some major 1987, Shaw 1988, Seaman et al. 1991, Davies and Day concentrations of pans. Pans are concentrated in, but not 1998). Pans usually dry up seasonally, mainly due to evap- restricted to, a pan ‘belt’ that stretches from the North West oration (Geldenhuys 1982). Their shape is circular to oval Province through the Northern Cape Province, and the west- (Allan 1987b). They are relatively shallow, even when fully ern Free State to south of the Orange River. In the western inundated, and usually less than three metres deep (Allan et Free State the belt runs southwards from Kroonstad, through al. 1995). ‘Playa’ is the most common name for a pan used , and to south of Kimberley in world geomorphological literature (Neal 1975, Davies and in the Northern Cape Province (Goudie and Thomas 1985, Day 1998), which is Spanish for shore (Waisel 1972). Seaman 1987, Shaw 1988). Pans are physically unstable, changing in a season or The pan density is particularly high in the even in a single rainstorm which can cause them to fill with Dealesville– area, according to Goudie and water. Plant and animal species in the pan change accord- Thomas (1985), and this is the area in which the Soetdoring ing to the depth, duration and volume of flooding, surround- Nature Reserve falls. Geldenhuys (1982) determined the ing topography and soil types. Thus, pans provide classic numbers and densities of pans per sixteenth degree square examples of ecological succession, where a plant communi- in the western Free State, and found that in the 2826 CC 402 Janecke, Du Preez and Venter square, in which a part of Soetdoring Nature Reserve falls, the Modder River (Figure 1). A shallow branchlet, that con- a total of 69 pans can be found, with a density of 10.2 pans tains water most of the time, splits off from the river close to per 100km–2. each of the pans. When the river is in flood, the water push- Several classification schemes of pans exist in South es up into these branchlets and eventually overflows into the Africa (Allan et al. 1995), those according to vegetation two pans. The southern pan is also part of a palaeo-drainage structure being the most commonly used (Noble and line of the river (Grobler et al. 1988). This pan is further char- Hemens 1978, Geldenhuys 1982, Allan 1987a). These acterised by having two man-made earth dams and a hot schemes have been loosely based on the vegetation asso- spring in its basin. The lay-out of the southern pan is pre- ciated with pans, but very few published analyses of the veg- sented in Janecke (2002). etation exist for South Africa. A comprehensive, although unpublished, survey of the vegetation of a pan is that of Methods Zimbatis (1975) covering Barberspan, near Delareyville in the North West Province. These results, however, refer to The classification of the vegetation was done on the basis of the entire Barberspan reserve and include both aquatic and the floristic-sociological (Zurich-Montpellier) approach or terrestrial plant species. An additional, but superficial, Braun-Blanquet method. The essential viewpoint of this description of the Barberspan flora is provided by Milstein method is that plant communities are units of classification, (1975). More recently, Fuls (1993) and Malan (1998) includ- based primarily on species composition (Kent and Coker ed the vegetation of some pans encountered in the northern 1996). In order to accommodate the growing season, sam- and southern Free State, respectively, in their study, while pling was conducted in the spring and summer of Meintjies (1992) gave a broad description of the vegetation 2000–2001. Plot sizes were fixed on 16m2 and stratified ran- of the Bainsvlei pans, near Bloemfontein. These three men- dom plots were used in order to accommodate the different tioned surveys are, however, unpublished. Parris (1984) zones in the pan. In each sample plot all species present gave a broad description of the vegetation associated with were recorded and the cover abundance of each species, pans in the Kalahari (South Africa and Botswana). Allan et according to the Braun-Blanquet scale (Mueller-Dombois al. (1995) provide the only other published data that could be and Ellenberg 1974), was noted. Species with less than five found for pans in South Africa, in the form of a list of ninety- occurrences, in the total data set of 55 relevés, were con- seven plant species recorded in the former Transvaal sidered to be of too low frequency to make a significant con- Highveld, (North West Province, Gauteng and tribution to the communities and have subsequently been Mpumalanga). omitted. A complete list of these species are given in The aims of this study were to identify, classify and Janecke (2002). Taxon names conform to the PRECIS describe the plant communities of the pans in Soetdoring species list of the NBI (updated in August 2001), as incor- Nature Reserve and to compare them to the vegetation of porated in the TURBOVEG database (Hennekens 1996a) of the hot spring and earth dams inside one of the pan basins. southern African flora. This study is important in providing information on the vege- The classification algorithm TWINSPAN (Hill 1979) was tation associated with pans, since very little information is applied to the floristic data set and then refined by applying available for the Free State at present. Braun-Blanquet procedures in the MEGATAB table editing program (Hennekens 1996b), in order to compile a phyto- Study Area sociological table (Table 1). Amongst others, these proce- dures were successfully used by Van Wyk et al. (2000) and Soetdoring Nature Reserve is situated about 34km north- Malan et al. (1994) for wetland areas. west of Bloemfontein, Free State Province, between lati- tudes 28°48’–28°53’S and longitudes 25°56’–26°07’E. The Results Bloemfontein–Dealesville road in the west and the Bloemfontein–Bultfontein road in the east bound the Five plant communities were recognised (Table 1) between reserve. The average altitude is 1 450m. The reserve covers the two pans, including the freshwater areas inside the a total surface area of 6 173ha and is situated around the basin. The hierarchical classification is as follows: Modder River and Krugersdrift Dam (Figure 1) (Watson 1. Cynodon transvaalensis–Gnaphalium declinatum community 1993). 1.1 Hemarthria altissima–Cyperus denudatus subcom- The reserve is underlain by the Tierberg Formation of the munity Ecca Group (Karoo Supergroup) (Van Riet et al. 1997). The 1.2 Selago dinteri–Cynodon transvaalensis subcommunity Tierberg Formation consists of shale, siltstone and sand- 1.3 Panicum schinzii–Cynodon transvaalensis subcom- stone. An extensive layer of sand, of aeolian origin, obscures munity the Ecca Group over a part of the reserve. Alluvium and 1.4 Portulaca oleracea–Cynodon dactylon subcommunity scree can be found next to the river (Nolte 1995). 1.5 Eleusine coracana–Cynodon dactylon subcommunity Soetdoring Nature Reserve falls in the Grassland Biome 2.Diplachne fusca–Eragrostis bicolor community (Rutherford and Westfall 1994). The vegetation type in the 2.1 Diplachne fusca subcommunity reserve is Dry Sandy Highveld Grassland, according to Low 2.2 Eragrostis bicolor–Diplachne fusca subcommunity and Rebelo (1996), and Dry Cymbopogon–Themeda Veld 2.2.1 Polygonum aviculare–Eragrostis bicolor variant (A50), according to Acocks (1988). 2.2.2 Sporobolus ioclados–Eragrostis bicolor variant There are two pans present, one in the northern part and 3.Helictotrichon turgidulum–Phyla nodiflora community the other in the southern part of the reserve, on each side of 4.Juncus rigidus community South African Journal of Botany 2003, 69(3): 401–409 403 5 | | | 4.4 | 4.3 4 | 4.2 | 4.1 | | 3 ||| | | | || | 2.2 2 2.2.1 2.2.2 | | 2.1 ....|...|..|..| 1b|4...4.|...|...... |... || | | 1.5 | 1.4 | | | | |||| | | | | || | | | | |||| | |||| | | | | | | | | | | 1.3 1 | | 1.2 | | 1.1 2222| 443223| 3332133| 223| 131| 1445| 444| 13| 1| 11| 553333| 333333| 3333333| 333| 55| 333| 3333| 333| 33| 33| 51| 33| 45 333333| 333| 333333| 333 155| | | | || ||b554|...... |...... |...|...|....|...|..|..|..|...... |...|...... |... || 1.b+|...... |...... |...|...|....|...|..|..|..|...... |...|...... |... 1...|...|..b|....|...|..|..|..|...... |...|...... |... | 5..3|...... |... | |....|...... | | 145b.41|...|.b.|....|...|..|..|..|...... |...|...... |... |....|...... |b11b511|...|...|....|...|..|..|..|...... |...|...... |... 1..1..1|...|...|....|...|..|b.|..|...... |...|...... |... |. 1..|...... | |....|...... | 3....+r|...|...|....|...|..|..|..|...r..|...|...... |... |....|...... |...... |bb1|...|....|...|..|..|..|...... |...|...... |... |....|...... |...... |. 33|...|....|...|..|..|..|...... |...|...... |... |....|...... |...... |. 1+|...|....|...|..|..|..|...... |...|...... |... |....|...... |...... |.b.|...|....|...|..|..|..|...... |...|...... |... |.. 3b3|....|...|..|..|..|...... |...|...... |... 1.|...... |...... |...| |....|...... |...... |...| 1.+|....|...|..|..|..|...... |...|...... |... | . b. . | 555555| 4bbb. 35| 5. 1| . 3. | .1|..4..4..+|1+1|14.|....|...|..|..|..|...... |...|...... |... |.b1.|..+..4|... 33|1.b|....|...|..|..|..|...... |...|...... |... |....|...... | 1..1+.+|. 1b|....|...|..|..|..|...... |...|...... |... |... 1|...... |...b...|...|. |....|...... |...... |...|...|b...|...|bb|.b|..|...... |...|...... |... |....|...... |...... |...|...|....|...|bb|..|..|...... |...|...... |... 1|443|33|..|..|b.....|...|...... |... |....|.....b|+...... |...|...|... |....|...... |...... |...|...|....| 111|1.|..|..|...... |...|...... |... | 8967| 108017| 2455936|| 341| 203| 7569| 234| 49|| 18| 56| 755686| | 831| 929001| 234 || 7777| 777777| 7777777|| 777| 777| 0000| 7777| 110000| 777| 0000000| 77|| 000| 77| | 000| 77| 8988| 0111| 777777| 009889| 111| 777| 9998899| 01| 777777|| 889| 00| | 777 797| 00| 9078| 7002| 110011| 219128| 000| 010| 3566047| 70| 110011| 452| 67| 000 314| 77| 8670| 116611| 345| 617| 50| 117711|| 29| 666 67| 866797| 942| 030112| 345 | | | | | | | |||| | |||| | | | | | | | | | | ------|------Phytosociological table of the vegetation in the pans (playas) of Soetdoring Nature Reserve (playas) of Soetdoring in the pans of the vegetation Phytosociological table Species Group A Hemarthria altissima Xanthium strumarium Cyperus denudatus Species Group B Panicum schinzii Echinochloa holubii Verbena brasiliensis Frankenia pulverulenta Species Group C Portulaca oleracea Cotula microglossa Chenopodium murale Limosella longiflora Species Group D Eleusine coracana Bulbostylis burchellii Species Group E Cynodon transvaalensis Variant number Gnaphalium declinatum Alternanthera sessilis Agrostis lachnantha Species Group F Sporobolus ioclados Salsola glabrescens Species Group G Eragrostis bicolor Lycium horridum Database nr.------| Number in table Community number Subcommunity number Table 1: Table 404 Janecke, Du Preez and Venter 5555| ...... |... bbb| 5534| . 33| 5131b. | ...... |...|...... |.. 4 4454| 334| b. | . . | . . | |....|...... |...... |...|...|....|...|..| 14|..|...... |...|...... |... |....|...... |...... |...|...|....|...|..|b+|..|...... |...|...... |... |....|...... |...... |...|...|....|...|..|b.|..|...... |...|...... |... |....|...... |...... |...|...|....|...|..|. 1|..|...... |...|...... |... |....|...... |...... |...|...|....|...|..|..|+3|...... |...|...... |... |....|...... |...... |...|...|....|...|..|.b|bb|...... |...|...... |... |....|...... |...... |...|...|....|...|b.|..|..|...... | 434|3.....|... |....|.. 1+1b|...... |...|...|....|...|b.|..|..|...... | |....|...... |...... |...|...|....|...|..|..|..|...... |...|bb |....|...... |...... |...|...|....|...|..|..|. 1|4b 4....|... |....|...... |...... |...|...|....|...|..|..|..|...... |...|...... | 44b 5.|45|b5..34|b..|. 3|..| |....|...... |...... | 111|3.4|....|.. 1+..|....b.1|b..|b1b|....|..b|..|bb|bb|.b..bb|...|...... |... |... 1|.. 1.b|b..|...|+...|1b1|..|..|bb|b1b1.b|...|...... |..b 1+.|.... |. 1..|... |....|...... |...... |...|...| Species Group I Helictotrichon turgidulum Species Group L Phragmites australis Panicum coloratum Eragrostis plana Eragrostis obtusa Species Group J Cyperus bellus Eragrostis biflora Species Group K Digitaria eriantha Selago dinteri Species Group M Juncus rigidus Species Group N Sporobolus virginicus Species Group O Cynodon dactylon Phyla nodiflora Polygonum aviculare Species Group H Diplachne fusca Table 1 cont. Table with an occurrence of less than five have been omitted from the table Species South African Journal of Botany 2003, 69(3): 401–409 405

Dealesville N Bultfontein

Krugersdrift Dam

Bloemfontein

Johannesburg 10km Bloemfontein NORTHERN PROVINCE Bloemhof Pietersburg 2 BOTSWANA MPUMALANGA Pretoria Nelspruit Bethlehem NAMIBIA Mafkeng Johannesburg 3 Harrismith NORTH WEST GAUTENG Klerksdorp 4 Kimberley 1 Upington KWAZULU- Kimberley Bloemfontein NATAL FREE Pietermaritzburg BLOEMFONTEIN STATE LESOTHO Durban NORTHERN CAPE Umtata ATLANTIC OCEAN EASTERN CAPE INDIAN OCEAN Bethulie East London WESTERN 5 Cape Town CAPE Cape Town Port Elizabeth Mossel Bay LEGEND Pans 1 - Soetdoring Nature Reserve Entrance Gate 2 - Sandveld Nature Reserve Picnic Spots 3 - Willem Pretorius Nature Reserve Lion and Wild Dog Camps 4 - Sterkfontein Dam Nature Reserve 5 - Tussen die Riviere Nature Reserve

Figure 1: Map of Soetdoring Nature Reserve and its location in the Free State Province, Republic of South Africa, in relation to other nature reserves. The dotted lines indicate public and maintenance roads

4.1 Cyperus bellus–Eragrostis biflora subcommunity characteristic feature is evident around the Mixed Grass 4.2 Cynodon transvaalensis–Juncus rigidus subcommunity Pan. On the outer edge a gray coloured concentric zone 4.3 Digitaria eriantha–Selago dinteri subcommunity occurs, consisting mostly of Gnaphalium declinatum and 4.4 Phragmites australis–Juncus rigidus subcommunity Phyla nodiflora. Inside this ring, a zone dominated by 5.Sporobolus virginicus community. Cynodon transvaalensis is found, while the pan basin is cov- ered by a mixture of grasses, such as Panicum schinzii and Description Echinochloa holubii. In contrast, no concentric zonation occurs in the Open Diplachne Pan, except that the vegeta- According to the classification schemes of pans (Noble and tion of the pan dune differs from that of the basin in having Hemens 1978, Geldenhuys 1982, Allan 1987a), the pan in a mixture of dwarf karroid shrubs, like Chrysocoma ciliata, the northern part of the reserve, with its thick growth of Salsola glabrescens and Rosenia humilis; grasses like hygrophilous grasses, is classified as a Mixed Grass Pan, Themeda triandra, Eragrostis trichophora, Digitaria eriantha, while the southern pan, with its brackish conditions and Cynodon dactylon, Chloris virgata and Aristida adscension- dominant Diplachne fusca, is classified as an Open is; as well as some species from the pan basin, namely Diplachne Pan. Diplachne fusca, Sporobolus ioclados, Eragrostis bicolor One of the characteristic features of the vegetation of pans and Cynodon dactylon; and others (Janecke 2002). These is the concentric zonation of the vegetation around a pan, relevés were not included in the table, because of the eco- caused by physical and chemical gradients in the soil tonal nature of the pan dune. (Leistner 1967, Parris and Child 1973, Parris 1984). This Pan ecosystems can pass through many successional 406 Janecke, Du Preez and Venter stages, emphasising their dynamic yet ephemeral nature schinzii, Echinochloa holubii (Species Group B) and (Maltby 1986). It is therefore important to note that the com- Cynodon transvaalensis (Species Group E) are dominant munities described here may not be representative of all the and jointly cover the entire basin. These are hygrophilous successional stages, but only of the final stage present in grasses, typical of pans or vleis (Van Oudtshoorn 1999). the dry phase of the pan, before it is inundated again. The Panicum schinzii is a highly palatable grass, Cynodon trans- vegetation associated with the Mixed Grass Pan is repre- vaalensis has relatively high grazing value, while sented by community 1, excluding the Eleusine coracana– Echinochloa holubii has an average grazing value (Van Cynodon dactylon subcommunity (1.5), and the vegetation Oudtshoorn 1999). Verbena brasiliensis (Species Group B) associated with the Open Diplachne Pan by communities 2 also occurs frequently between the grasses, while Frankenia to 5 and subcommunity 1.5 (Table 1). pulverulenta (Species Group B), Polygonum aviculare and Phyla nodiflora (Species Group O) are occasionally found in 1. Cynodon transvaalensis–Gnaphalium declinatum the pan basin. community This community (Species Group E) characterises the vege- 1.4 Portulaca oleracea–Cynodon dactylon subcommunity tation of the freshwater Mixed Grass Pan. Cynodon trans- This subcommunity occurs on damp soil in the area between vaalensis is dominant and covers large areas of the pan the Mixed Grass Pan and the short, shallow branchlet from basin and also occurs in the inner concentric zone on the the river, filled with stagnant water. Mostly pioneer species, edge of the pan. This zone is characterised by the grayish such as Portulaca oleracea, Cotula microglossa, forb Gnaphalium declinatum, together with Alternanthera Chenopodium murale and Limosella longiflora (Species sessilis and Agrostis lachnantha (Species Group E). The Group C), characterise this subcommunity. The high cover Cynodon transvaalensis–Gnaphalium declinatum communi- values of Alternanthera sessilis (Species Group E) and the ty subdivides into the following five subcommunities. high constancy of Cynodon dactylon (Species Group O) are also diagnostic. Cynodon dactylon is a pioneer grass often 1.1 Hemarthria altissima–Cyperus denudatus subcommunity found in damp places, but not restricted to them (Van This hygrophilous subcommunity is not part of the vegeta- Oudtshoorn 1999). Cynodon transvaalensis, Gnaphalium tion of the Mixed Grass Pan basin itself, but occurs on the declinatum (Species Group E), Phyla nodiflora and edge of the pan on damp soil, between the pan and the Polygonum aviculare (Species Group O) were also encoun- Modder River. The diagnostic species of this subcommunity tered in varying densities. are given in Species Group A. Hemarthria altissima is the dominant species and is a highly palatable, creeping, mat- 1.5 Eleusine coracana–Cynodon dactylon subcommunity forming grass (Van Oudtshoorn 1999). Hemarthria altissima This subcommunity occurs in the Open Diplachne Pan on prefers wet areas such as vleis (or swamps) or river banks the banks of the one earth dam. The earth dam is perma- and is always found growing in or near water (Van nently inundated, thus its vegetation differs from that of the Oudtshoorn 1999). Cyperus denudatus, a sedge, is usually surrounding ephemeral pan, as well as from the vegetation also associated with water and occurs in dense stands of the shallow branchlet from the river that fills and retreats. between Hemarthria altissima. Xanthium strumarium, or Eleusine coracana (Species Group D) is dominant. The cocklebur, occurs in high densities but is a Category 1 invad- diagnostic species of this subcommunity are those of er weed. This means that Xanthium strumarium is an unde- Species Group D, while prominent species include Cynodon sirable plant and must be eradicated (Bromilow 2001). transvaalensis, Gnaphalium declinatum, Alternanthera ses- silis (Species Group E), Cynodon dactylon and Phyla nodi- 1.2 Selago dinteri–Cynodon transvaalensis subcommunity flora (Species Group O). This subcommunity was mostly present on the edge of the Mixed Grass Pan, between the pan and Acacia karroo thorn- 2. Diplachne fusca–Eragrostis bicolor community veld. No diagnostic species occur, but the subcommunity dif- This community characterises the vegetation of the Open fers from other subcommunities with respect to the absence Diplachne Pan’s basin. It does not, however, cover the of Species Groups A–D and the presence of Selago dinteri whole basin. There are bare patches where high salt con- (Species Group K). Cynodon transvaalensis (Species Group centrations, visible as crystals on the unvegetated soil sur- E) has high cover abundance values. Eragrostis bicolor face, are present. Diplachne fusca (Species Group H) is the (Species Group G), Gnaphalium declinatum (Species Group dominant and diagnostic species in the pan and occurs in E), as well as Phyla nodiflora and Polygonum aviculare varying densities. Other species that frequent the pan basin, (Species Group O) are scattered throughout the subcommu- are Eragrostis bicolor, Lycium horridum (Species Group G) nity. and Polygonum aviculare (Species Group O). This commu- nity also covers the lunette dune on the north-western side 1.3 Panicum schinzii–Cynodon transvaalensis subcommunity of the pan that merges into the grassland. The following two The vegetation of this subcommunity covers the basin of the distinct subcommunities are included in the Diplachne fusca Mixed Grass Pan, excluding the circular zones on the out- –Eragrostis bicolor community. side. No salt precipitate is visible on this pan’s basin. The presence of this subcommunity contributes largely to the 2.1 Diplachne fusca subcommunity classification of the pan as a Mixed Grass Pan. The species This subcommunity is typical of the pan basin. The habitat is of Species Group B is diagnostic. The grasses Panicum that of extremes with dry, hot, brackish conditions when the South African Journal of Botany 2003, 69(3): 401–409 407 pan is dry, in contrast to the conditions when it is inundated. Group I) is dominant, along with Cynodon dactylon and These conditions may even be present at the same time in Phyla nodiflora (Species Group O). Panicum coloratum, different parts of the pan. These extreme conditions elimi- Eragrostis plana (Species Group I), Eragrostis biflora nate almost all plants, except Diplachne fusca, from growing (Species Group J), Verbena brasiliensis (Species Group B), in the habitat. It is one of very few grass species that grow Sporobolus ioclados (Species Group F) and Eragrostis successfully in habitats with brackish soils that are periodi- obtusa (Species Group I) also occur in the community with cally inundated (Van Oudtshoorn 1999). The high cover varying cover abundance values. Except for the forb abundance values of Diplachne fusca (Species Group H) Verbena brasiliensis, the others are all grass species of and the absence of all other species, except Sporobolus moist grassland (Van Oudtshoorn 1999). ioclados (Species Group F), Eragrostis bicolor (Species Group G) and Polygonum aviculare (Species Group O), are 4. Juncus rigidus community diagnostic in this subcommunity. This community, characterised by Juncus rigidus (Species Diplachne fusca is a highly palatable, rhizomatous swamp Group M), surrounds and connects the hot spring and earth grass, with different growth forms (Van Oudtshoorn 1999). dam in the Open Diplachne Pan’s basin. The rush, Juncus The growth form in Soetdoring Nature Reserve is of a flat rigidus (Species Group M), forms an almost homogeneous creeping character — the culms are about 0.1m tall and the stand, where the few open spaces between the Juncus tus- inflorescences are 50mm long. However, Van Oudtshoorn socks are occupied by species like Cynodon transvaalensis (1999) described it as having culms 0.3–1.5m tall and inflo- (Species Group E), Polygonum aviculare (Species Group O) rescences 0.2–0.35m long. and Frankenia pulverulenta (Species Group B). According to Waisel (1972), the various species of Juncus 2.2 Eragrostis bicolor–Diplachne fusca subcommunity play an important part in the succession of saline habitats, This subcommunity (Species Groups G and H) can be found and under certain conditions form a long prevailing commu- in patches on the basin, as well as on the edge of the Open nity (sere climax), which will remain as long as the water Diplachne Pan. Diplachne fusca (Species Group H) is dom- table and salt levels are constant. Most species are inhabi- inant in the pan basin. The high cover values of Eragrostis tants of brackish water, but tend to avoid permanently inun- bicolor (Species Group G) is diagnostic. Eragrostis bicolor is dated habitats with stagnant water, and concentrate on the known to grow in pans, mostly in moist, brackish soils (Van fringes of salines (Waisel 1972). Chapman (1974) described Oudtshoorn 1999). Lycium horridum (Species Group G) the principal association of thermal saline areas in central occurs at low density throughout the pan basin. This sub- Africa as a Juncus rigidus–Sporobolus virginicus communi- community can be subdivided into the following two variants. ty, which shows some affinity with this community. The Juncus rigidus community consists of four subcom- 2.2.1 Polygonum aviculare–Eragrostis bicolor variant munities. The first two subcommunities occur at the earth This variant represents the vegetation of the basin of the dam and the others are associated with the hot spring of the Open Diplachne Pan where water remains for longer peri- Open Diplachne Pan. ods. Eragrostis bicolor (Species Group G) and Diplachne fusca (Species group H) are dominant, while Lycium hor- 4.1 Cyperus bellus–Eragrostis biflora subcommunity ridum (Species Group G) also has a high frequency. The The earth dam inside the basin of the pan is a permanent presence of Polygonum aviculare, Cynodon dactylon and water body, the vegetation of which completely differs from Phyla nodiflora (Species Group O), as well as the absence that of the pan (note the absence of the Diplachne fusca of all other species groups are characteristic of this variant. community (2). This subcommunity occurs on the disturbed soils of the dam wall and is characterised by the species of 2.2.2 Sporobolus ioclados–Eragrostis bicolor variant Species Group J. Cynodon dactylon (Species Group O) is This variant occurs on the edge of the pan and contains a dominant, while Cyperus bellus, Eragrostis biflora (Species mixture of vegetation from the pan basin and from that of the Group J), Phyla nodiflora, Polygonum aviculare (Species adjacent grassland. Species Groups F and K contain the Group O) and Cynodon transvaalensis (Species Group E) diagnostic species. Sporobolus ioclados (Species Group F) are rather prominent as well. is the dominant species, along with Salsola glabrescens (Species Group F) and Eragrostis bicolor (Species Group G). 4.2 Cynodon transvaalensis–Juncus rigidus subcommunity Sporobolus ioclados normally grows in and around seasonal This subcommunity occurs in the seepage area of the earth pans, since it is well adapted to brackish and other saline dam and is represented by Species Groups E and M. No soils (Van Oudtshoorn 1999). Diplachne fusca (Species diagnostic species occur, but the subcommunity is charac- Group H), Digitaria eriantha and Selago dinteri (Species terised by the absence of all species groups, except for Group K) have equally high cover values in the variant. Species Groups B, E, G, M and O. Juncus rigidus (Species Group M) is the dominant species, while Cynodon trans- 3. Helictotrichon turgidulum–Phyla nodiflora community vaalensis (Species Group E), Cynodon dactylon, Phyla nod- This community occurs in a disturbed area of the pan basin, iflora and Polygonum aviculare (Species Group O) also form where water is retained for longer periods than in the rest of a prominent part of the vegetation. The species of Species the basin. The site is next to a dirt road traversing the pan, Group O have a high constancy in this subcommunity. Phyla at a storm-water drainage pipe. The diagnostic species are nodiflora mostly occupies the zone next to the water’s edge, those of Species Group I. Helictotrichon turgidulum (Species while the other species are mostly present on the dam walls. 408 Janecke, Du Preez and Venter

4.3 Digitaria eriantha–Selago dinteri subcommunity etation zones are, however, not a feature of the brackish This subcommunity is associated with the vegetation of the Open Diplachne Pan on the southern side of the Modder hot spring in the Open Diplachne Pan. It occurs on elevated River. ‘islands’, isolated from the rest of the pan basin. The soil of The species composition of the two pans differs to a large these ‘island’ areas has a more sandy texture in comparison extent. The Mixed Grass Pan is characterised by a Cynodon to the clayey texture of the pan basin. No salt precipitate is transvaalensis–Gnaphalium declinatum community, associ- visible in these elevated mounts. The subcommunity can ated with the following subcommunities: Selago dinteri– also be found between the dense Phragmites australis Cynodon transvaalensis, Panicum schinzii–Cynodon trans- stand, that occurs around the eye of the spring, and the vaalensis and Portulaca oleracea–Cynodon dactylon sub- dominant stand of Juncus rigidus further away from the eye community. The Hemarthria altissima–Cyperus denudatus (Subcommunity 4.4). subcommunity is not really part of the pan vegetation, but Digitaria eriantha is the dominant species, with Selago rather represents riparian vegetation, as it occurs between dinteri also present in high densities (Species Group K). the pan and the river. Cynodon dactylon (Species Group O) occurs in small patch- The Open Diplachne Pan itself is characterised by a es on the islands. All the pan species, except Juncus rigidus Diplachne fusca–Eragrostis bicolor community with a (Species Group M), are absent (Species Groups A–J, L and Diplachne fusca subcommunity and an Eragrostis bicolor– N). These islands have a grassland character, therefore the Diplachne fusca subcommunity associated with it. The last mixture of grass species associated with Juncus rigidus. mentioned subcommunity is subdivided into two variants, namely the Polygonum aviculare–Eragrostis bicolor variant 4.4 Phragmites australis–Juncus rigidus subcommunity and the variant that represents the lunette dune vegetation This subcommunity represents the vegetation of the hot — the Sporobolus ioclados–Eragrostis bicolor variant. The spring. The spring at Vlakkraal 23 (a farm now incorporated Helictotrichon turgidulum–Phyla nodiflora community indi- into the reserve) is one of three mineral springs within a rel- cates a disturbed area inside the Open Diplachne Pan, while atively small area near the Modder River. The others are at the Sporobolus virginicus community represents only a and Lombards Drift 832, respectively — immedi- small area between the hot spring and the lunette dune, but ately east of the bridge on the tarred road (Grobler is absent from the rest of the pan basin. and Loock 1988). According to Kent (1949), all three springs The two earth dams inside the Open Diplachne Pan are are classified as warm springs. respectively characterised by the Eleusine coracana– Phragmites australis forms a dense stand around the eye Cynodon dactylon subcommunity of the Cynodon trans- of the spring in the reserve. There is no standing water visi- vaalensis–Gnaphalium declinatum community, and the ble, but the vegetation differs completely from that of the Juncus rigidus community along with its Cyperus bellus– ephemeral pan. Species Group L characterises this sub- Eragrostis biflora and Cynodon transvaalensis–Juncus community, along with Species Group M. Phragmites aus- rigidus subcommunities. This differs from the normal pan tralis (Species Group L) is the dominant species, with vegetation and rather represents vegetation of more perma- Juncus rigidus (Species Group M) the only other frequent nent water bodies. The hot spring is also characterised by species. Digitaria eriantha (Species Group K) and Cynodon the Juncus rigidus community, but along with the Digitaria dactylon (Species Group O) are found scattered between eriantha–Selago dinteri and Phragmites australis–Juncus these two dominant species. rigidus subcommunities. The pans of Soetdoring Nature Reserve justify conserva- 5. Sporobolus virginicus community tion, not only as habitat for animals and birds (Janecke This unique community occurs only in a small patch inside the 2002), but also by possibly helping to reduce floods further Open Diplachne Pan, located in the area between the hot downstream of the Modder River. Water from the overflow- spring and the lunette dune. The rhizomatous grass, ing river fills the pans, by means of branchlets and hence Sporobolus virginicus (Species Group N), characterises this they serve as storage areas for water. Consequently, the community, while the absence of almost all the other species pans inside the reserve are subjected to impacts from the listed on Table 1 is also notable. Diplachne fusca (Species catchment of the pans that lies outside the reserve. Group H) and Polygonum aviculare (Species Group O) are Drainage from ploughed fields situated in the pans’ catch- the only other species noted. Sporobolus virginicus is a halo- ments can introduce pesticides and fertilisers resulting in phytic, mat-forming, perennial grass with salt glands on its contamination and eutrophication, which is exacerbated by leaves (Naidoo and Naidoo 1998). Salt secretion in halo- the endorheic nature of these wetlands (Geldenhuys 1982, phytes is regarded as an adaptive mechanism to cope with Allan 1987b, Seaman 1987). Large areas of the Open high substrate salinity (Waisel 1972, Naidoo and Naidoo Diplachne Pan are not even in the natural state any more, 1998). Although this grass is common along the South African due to man’s previous actions, i.e. the creation of the per- coastal areas, the species may also occur inland around manent earth dams in the pan basin (Janecke 2002). Care saline water bodies, according to Naidoo and Naidoo (1998). should be taken that the pans are properly conserved inside the nature reserve. Discussion Acknowledgements — Special thanks to Dr PWJ van Wyk, A characteristic feature of freshwater pans seems to be the Department of Plant Sciences, for time and assistance in creating concentric zones of vegetation. The concentric zones may the figure. The management of Soetdoring Nature Reserve is thanked for assistance and kindness. indicate a sere of hygrophytic communities. Concentric veg- South African Journal of Botany 2003, 69(3): 401–409 409

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Edited by GJ Bredenkamp