Vegetation of high-altitude fens and restio marshlands of the Hottentots Holland Mountains, Western Cape, South Africa

Seepages occurring at high altitudes in the Hottentots Holland Mountains (HHM) (Western Cape Province. South Africa) were subject to a phytosociological survey. Relevé sampling method and classification procedures of the floristic-sociological (Braun-Blanquet) approach as well as numerical data analyses (numerical classification and ordination) were used to reveal syntaxonomic patterns and characterize the position of the syntaxa along major environmental gradients. Nine plant communities were recognized, three of which were classified as associations, following formal syntaxonomic and nomenclatural rules of the floristic-sociological approach Most of the studied mire communities were dominated by low-growing clonal restios (Restionaceae). whereas some consisted of other types of graminoids. The most important species determining the structure (and function) of the mire communities on sandstones of the HHM include restios Anthochortus crinalis, Chondropetalum deustum. C. mucronatum, Elegia intermedia. E. thyrsifera. Restio subtilis. R. purpurascens. cyperoids Epischoenus villosus. Ficinia argyropa, grasses Ehrharta setacea subsp. setacea. Pentameris hirtiglumis as well as shrubs Berzelia squarrosa. Cliffortia tricuspidata. Erica intenallaris and Grubbia rosmarinifolia. Protea lacticolor and Restio perplexus dominate a rare shale band seep­ age community. There are two major groups of communities—the fens (dominated by carpets of Anthochortus crinalis and other low-growing species) and the restio marshlands (mosaics of low tussocks of Restio subtilis and tall Chondropetalum mucrona­ tum). The degree of soil (and water) minerotrophy was found to be the most important differentiating feature between the mire (fen and restio marshland) communities studied. The soils in the centre of mires were found to have high contents of peat and showed very little influence from the underlying sandstone. The soils along the mire margins had a greater admixture of miner­ al soil derived from the sandstone or shale bedrock.


INTRODUCTION
The Cape mountain ranges are important catchments for high-quality drinking water. A vast quantity of this water is stored in the basement rocks before it is released into river systems via seepages (Hewlett 1982). Seepage is a very general term for an area where water percolates through the upper soil layers (mostly lying over a layer of impenetrable rock) and usually forms the source of rivers. It includes the majority of wet slopes as well as many mires of the Cape mountains. The quality of water is largely determined by the soil conditions that percolat ing water encounters prior to its emergence at the surface and on its way to a river, hence seepages are of great importance to river ecosystems (Bosch el al. 1986). However, the total surface area of seepages that influ ence the water quality of rivers is variable and many seepages can be out of touch with the river system for a long time. This was called the Variable Source Area Concept by Hewlett (1961). After heavy rains the Source Area of a river expands and much water, that was stored in basement rocks or in fens for a long time, moves into the river. During its storage in the seepage areas, water is stained by tannins leached from decaying plant litter. This explains the brown colour that is characteristic of many of Western Cape rivers, particularly after heavy rains (King & Day 1979;Dallas & Day 1993).
Some seepages located in high-altitude areas supporting fynbos vegetation have soils rich in peat -accumulated organ ic material (Gore 1983)-they can be classified as mires.
These are defined as wet. swampy habitats characterized by peat> soils, regardless of the chemico-physical properties of the peat and water captured in the peaty soils. Concepts such as bogs and fens refer to specific types of mires (Gore 1983). The term bog refers to the strictly ombrotrophic (rain-fed) and usually oligotrophic mires found in places with high pre cipitation. whereas fens are the mires (minerotrophic or tran sitional ) that are fed to a larger extent by water that has per colated through the mineral substrate. The Cape high-altitude mires generally qualify as fens; true bogs are rare in the south ern hemisphere, although they do occur on some steep southfacing slopes in Western Cape mountains. In the mountains, mires are found at the sources of the rivers and in watersheds. Riparian mires can be formed in places where the floodplain is very wide and the area remains inundated long after a flood has receded.
There are four types of seepages linked to the drainage network of rivenne systems recorded in the Cape moun tain ranges, namely; 1. well-drained slope seepages supporting soils of the Femwood form (Fry 1987); this type shows a high level of variability and can be characterized by the increased presence of Bruniaceae; Campbell (1986) in his structur al classification of the Fy nbos Biome. classified the veg etation of these seepages as Wet Ericaceous Fy nbos; 3, the high-altitudefens, situated at the sources of rivers: Campbell (1986) has classified the vegetation of this habitat as Sneeukop Azonal Restioid Fynbos and Otterford Wet Proteoid Fynbos; 4, in order to distinguish between the different degrees of minerotrophy in the mires described in this study, we want to introduce the term restio marshlands for the bet ter-drained sites at the edges of mires of the Fynbos Biome, in contrast to the 'fens' being situated in the cen tre of the mire. The restio marshland supports a vegeta tion structural type called Sneeukop Azonal Restioid Fynbos (Campbell 1986).
Most of the African swamps (including mires and other types of marshlands) are dominated by grasses and sedges (Van Zinderen Bakker & Werger 1974;Weisser & Howard-Williams 1982;Thompson & Hamilton 1983;Rogers 1995Rogers , 1997. The fens and restio marshlands of the Fynbos Biome are conspicuously different due to the dominance of (often endemic) Restionaceae (Campbell 1986). Despite their peculiarity, the wetland ecosystems of the Cape mountain ranges have received little atten tion (Boucher 1988;Rogers 1997) and hence deserve a closer look.
This study describes vegetation types found in the rare and poorly studied high-altitude fens and restio marshlands located in the region of richest precipitation in Western Cape-the Hottentots Holland Mountains (HHM). The floristic composition of these vegetation types and their relationship to major ecological factors are the main foci of this paper.

Study area: location, climate, geology and soils
The majority of vegetation samples used for this paper were recorded from the HHM (between 33° 56' S and 34° 03' S latitude and 18° 57' E and 19° 09' E longi tude). This area is situated between the towns of Stellenbosch, Franschhoek and Grabouw in Western Cape, South Africa-the region with the highest rainfall in Western Cape and possibly also in the entire South Africa. There are many peaks reaching above 1 000 m altitude, where numerous and extensive mires have developed. We have added some additional vegetation samples from the Du Toitskloof Mountains, which are located to the north of the HHM and some from the Groenland Mountains, southeast of the HHM.
Most of the fens in the HHM are found in the Palmiet River catchment, although the Riviersonderend and Eerste Rivers are fed by water from fairly extensive mire systems. Two other rivers originating in the area, the Berg River and the Lourens River, barely receive water from mires as they originate on very steep mountain headwalls.
The climate of the Fynbos Biome in the southwestern Cape is classified as mediterranean, with hot, dry sum mers and mild, wet winters. In the Kóppen (1931) system the climate of the area is classified as Csb-having mesothermal (C) climate with a warm, dry summer and average temperatures above 22°C and relatively wet win ters (sb). Most mountains of the Fynbos Biome have a rainfall between 1 000 and 2 000 mm mean annual pre cipitation (MAP), but in the wettest areas (such as the HHM) it might exceed 3 000 mm (Schulze 1965). Most low-lying localities receive much less-up to 750 mm near the coast, and mostly less than 400 mm MAP in the intermontane valleys (Fuggle & Ashton 1979). The mountains in the Fynbos Biome play a major role in influencing precipitation and evaporation. Extremely high regional variation in precipitation ( Figure 1) occurs due to the windward-leeward geomorphological dichoto my in the mountains and the fact that winds can sweep unhindered over the coastal plains (Deacon et al. 1992). Schulze (1965) described a strong gradient in rainfall with increasing altitude-50 mm of precipitation increase per 300 m increase in altitude. The regional rainfall pattern in the mountains is variable, depending on aspect of slope as well as frequency and strength of northwesterly and southwesterly winds. Mountains can

18*4ff
19*12- Computing Centre for Water Research; grid data comput ed from weather data from nine official weather stations in vicinity, extrapolated using methodology of Dent et al. 1987). also receive much precipitation (not registered in the rain gauges) from mist (Kerfoot 1968;Fuggle & Ashton 1979) associated with the summer trade winds, locally known as 'southeasters'.
Sixty per cent of the precipitation falls in the wettest four months spanning June to September. This precipita tion is mostly in the form of rain, but snow regularly occurs in winter on the mountain peaks (Fuggle & Ashton 1979). Wind speeds are the highest in winter on the mountain tops (Fuggle 1981). This is in contrast with the wind patterns in the surrounding lowlands, showing the highest speed in summer.
The geology of the HHM is dominated by sandstones and shales of the Table Mountain Group, especially at the higher altitudes. Some of the valleys are underlain by Achaean Cape Granite and Malmesbury Group shales, but no mires were recorded on these latter substrates. The Table Mountain Group sandstones (TMS) are mainly from the Nardouw Formation (De Villiers et al. 1964). High-altitude shale bands of the Cederberg Formation accompanied by tillites of the Pakhuis Formation occur throughout the area. The shale bands are situated at high er altitudes than most of the seepage areas and virtually all the vegetation types (with one exception) described in this study, are reported from sandstone.
Soils of the mires are classified as belonging to the Champagne Form (Soil Classification Working Group 1991). The amount of peat is variable; towards the outer edges of seepages, the soil contains a greater portion of minerotrophic material (mainly sand) originated from sandstone. Here the prevailing soil form is the Femwood Form. In this study, we have used soils as a major crite rion for the location and delimitation of the fens.

Methods of data collection
Vegetation was studied by means of plot sampling. The plots were laid out in selected fen and marshland habitats in a representative way (Westhoff & Van der Maarel 1978). The size of most of the plots was 10 x 10 m (sometimes less in the case of small vegetation stands), as this was considered to be sufficient to record the species richness. In each plot, each plant species was recorded and the cover-abundance of each was esti mated using the modified Braun-Blanquet sampling scale (Barkman et al. 1964). Thirty-three plots were recorded in the HHM. We also added a further two sam ples from the Du Toitskloof Mountains merely to point out that similar communities also occur in the neigh bouring mountain ranges (Appendix 2). Soil samples were only collected from the topsoil (A-horizon). The particle size distribution of the soils is determined for the fractions finer than 2 mm 0 . After drying and grind ing the soil to break up any coagulation, the soils were shaken through a set of sieves. The sieves of the fol lowing raster size were used: 500 ^m (to separate coarse sand), 106/vm (to separate medium sand) and 63 pirn (to separate fine sand). The fraction that passes through all the sieves is composed of silt and clay. Acidity and resistance were measured in water-saturat ed soils using a pH meter (Orion 420A) and a conduc tivity meter (YSI 3200). The fraction of organic matter was measured by titration according to the Walkley-Black method (Walkley 1935; Non-Affiliated Soil Analysis Work Committee 1990).
A list of environmental variables and other relevant information is presented in Table 1. Altitude (ALTITUDE) R IX*termined from orthophotographic maps (scale 1:10 000); expressed in m.

Resistance (RESISTAN) R
Resistance to an electrical current (£2) measured using a YSI model 3200 conductivity meter.

Methods of data handling and presentation
The vegetation samples were stored in a database in the format of the National Vegetation Database (Mucina et al. 2000) and using the database-management software Turboveg (Hennekens 1996b;Hennekens & Schaminée 2001). The original cover-abundance data was trans formed into percentage format using Turboveg. The data were classified using Two-way Indicator Species Analysis (TWINSPAN) (Hill 1979) followed by manual table-sorting using MEGATAB 2.0 (Hennekens 1996a), aimed at improvement of coincidence between the groups of relevés and groups of species. Differential species for communities and their groups were identified on the basis of fidelity. The differential species, constant companions and the dominant species are identified in each case. A dif ferential species is a species that can be used to differenti ate between one community or a group of communities and the rest at the same syntaxonomic level (Westhoff & Van der Maarel 1978;Mucina 1993). The difference in the frequency of more than two presence classes (40%) was taken as sufficient for a species to be considered to be dif ferential for one of the communities under comparison. However, a species can also be ranked as differential on the basis of distribution of cover values (dominant versus non-dominant) among relevés of the communities under comparison. A dominant species is a species that is con stant and has an average cover of more than 25% (Westhoff & Van der Maarel 1973). A constant companion is a species that occurs in more than 60% of all the sam ples in a community and is not considered differential at the same time. Less frequent species recorded in plots are listed in Appendix 1. The communities are described here at the level of association or rankless vegetation type com parable to the level of association. We refrained from defining units of the higher syntaxonomic ranks due to limited extent of the data and local character of the study. We have used only two informal groups of the communi ties based on the habitat characteristics (fens vs. restio marshlands).
The relationship between the environmental data and the vegetation data was determined using multivariate techniques. We follow 0kland (1996), who made a case for validity of use of both ordination and constrained ordination as complementary approaches, both direct and indirect gradient analyses were performed The four vari ables, coarse sand, medium sand, fine sand and silt, together comprise 100% in every soil sample so they are not independent from each other. According to the rec ommendations of Ter Braak & Smilauer (1998) this sort of (compositional) data, has to be log-transformed prior to analysis. Correspondence Analysis (CA) was adopted as the indirect gradient analysis technique, while Canonical Correspondence Analysis (CCA) was used to perform the direct gradient analysis (see Ter Braak 1986;Jongman et al. 1987 for details on the techniques). The Canoco 4 program suite (Ter Braak & Smilauer 1998) was used to perform CA and CCA.

Nomenclature of taxa and plant communities
The nomenclature of plant species follows Germishuizen & Meyer (2003). Three of the well-sampled plant communities were named according to the rules for syn-taxomic nomenclature (Weber et al. 2000). Vernacular names, using a combination of important taxa and veg etation structure (Edwards 1983), were coined for all plant communities as well.

RESULTS
The fens (and most of the restio marshlands) of the region have a high cover of Restionaceae. Only a few seep age types are dominated by grasses or sedges, such as Carpha glomerata, Epischoenus spp., lsolepis prolifer and Pennisetum macrourum. Some Restionaceae typically occurring in the seepages are Anthochortus crinalis, Chondropetalum mucronatum, Elegia thyrsifera and Restio subtilis. Two graminoids such as Ehrharta setacea subsp. setacea and Epischoenus villosus are also common.
The following Community Groups and Communities have been revealed in our data:

Community Group A: Fens
Fens form the wettest parts of the seepages-they are poorly drained and contain much peat. The low-grown restio Anthochortus crinalis is usually dominant and forms dense mats in between the tussocks of cyperoid Epischoenus villo sus. Five fen communities were distinguished: the Communities A 1 and A2 occur on steep slopes and experi ence somewhat better drainage than the flat-habitat fen com munities (Communities A3, A4 and A5).

Community A l: Protea lacticolor-Hippia pilosa Tall Shrubland
( The Community Al is peculiar due to its link to shale bands. Protea lacticolor is the dominant species and forms a dense shrubbery 2-4 m tall. This is the only form of proteoid fynbos recorded on the slope seepages in HHM. The herb layer covers over 80% and is dominated by tussocks of Epischoenus villosus and mats of Restio per plexus. Other important species include Senecio umbellatus, Seriphium plumosum ( = Stoebe plumosa), Hippia pilosa and Oxalis truncatula. The stands of this community were recorded on the eastern slopes of Somerset Sneeukop at a very high altitude (about 1 400 m). The habitat receives a very high annual rainfall (more than 3 300 mm), some of it in the form of snow, which might persist longer on the southern than on the northern slopes of the mountain. A dense mist blanket covers the mountain especially in sum mer. It is purported to contribute a considerable additional amount of ambient precipitation (Marloth 1903). Campbell (1986)  This community is found near the sources of the Lourens River on the western slopes of Somerset Sneeukop (1 1 (X) m) at high altitudes and receives a high precipitation. The upper herb layer is formed by the dom inating Elegia thyrsifera, whereas the lower herb layer is formed by a multitude of species, such as Senecio umbellatus. Hippia pilosa and Erica curviflora. This communi ty, like the Protea lacticolor-Hippia pilosa Tall Shrubland, is quite atypical for the seepages of the studied area. The differential species, Carpacoce spermacocea. Centella eriantha, Othonna quinquedentata and Ursinia eckloniana, are all more common in typical ericaceous fynbos (Sieben 2003). The Elegia thyrsifera-Centella eriantha Commu nity occurs on steep slopes on sandstone. This is an extremely species-poor seepage communi ty, which is limited to the Dwarsberg Mountains in the Berg River catchment. The dominant vegetation stratum is a dense layer of Elegia intermedia, which grows 1.2 to 1.5 m tall. Linder (1987) has not recorded this species outside the Cape Peninsula, but Kruger (1978) found it on the Dwarsberg. In this study, it was recorded in several other locaties in the HHM. The lower herb layer of the community is dominated by Anthochortus crinalis and is less dense. Dwarsberg receives more than 3 000 mm rainfall per annum and the community is found in the wettest, extremely peaty habitats, surrounded by stands of the Ficinio argyropae-Epischoenetum villosi and Tetrario capillaceae-Restietum suhtilis. Epischoenus villosus, Senecio crispus and the moss Campylopus stenopelma as well as the species mentioned above are the only species present in the vegetation. This is one of several seepage communities dominat ed by the restio Anthochortus crinalis. This clonal spe cies forms dense mats and is often found intertwined with Ehrharta setacea subsp. setacea, Cliffortia tricuspidata and Senecio crispus. The vegetation is much short er than in the previous communities. The tallest restio present is Elegia grandis. which grows taller than 0.5 m together with the tussocks of Epischoenus villosus. In the limited open spaces, low-grown Ficinia argyropa and Anthoxantum tongo can be found. This community as well as the Community A5. resemble similar vegetation described from the A further seepage type is also dominated by Anthochortus crinalis. Floristically and structurally this community resembles the previous one closely and it might also be considered as a subassociation of the Ficinio argyropae-Epischoenetum villosi. The main dif ference is in the absence of Senecio grandiflorus and Ficinia argyropa. but this community also has some dif ferential species of its own, such as Gladiolus carneus, Restio bifurcus. Restio corneolus, Tetraria capillacea and Chondropetalum mucronatum (the last-named reaches far above the dominant herb layer). Notable is the occurrence of Prionium serratum -a typical shrub in Cape mountain streams (Sieben 2003).

Community Group B: Restio Marshlands
The habitats supporting all four communities of Com munity Group B are better drained than those of Com munity Group A. The soils are largely of minerotrophic origin and the peat content is low. They are often found on the edges of the mires and the water drains into the fens. The restio marshlands are richer in species than the fens. The Communities B 1 and B2 show transitional fea tures between restio marshlands and fens, through occur rence of species such as Senecio crispus. (Table 2.

relevés 19-21)
This is the only seepage type dominated by restio Platycaulos depauperatus. which forms dense green mats and is the most conspicuous differential species of this community. The tussock-forming Restio subtilis is the co-dominating element. Together they form the lower herb stratum. One emergent 1.5 m tall restio. Chondro petalum mucronatum. forms its own stratum. Epischoe nus villosus. Elegia neesii and Tetraria capillacea are significantly shorter. Apart from the eponymous, the only other differential species of this community are the grass Pentameris hirtiglumis and the geophyte Kniphofia tabu laris, flowering after a fire. We believe that this community, although only recorded in our study in three samples, due to being visible after a recent fire, is quite common in the Palmiet River catchment. It seems to occupy an intermediate ecological position between the Ficinio argyropae-Epischoenetum villosi Association (from peaty soils) and the Tetrario capillaceae-Restie tum subtilis Association (from more minerotrophic soils). The localities of this community receive less rain fall than other seepage types, with a MAP of just over 2 (XX) mm.
" >c (N --X r~X u u. H < i r. -< r. -X 3Cr~r-2= 0£ tt. E-< i r.   (Table 2, relevés 22, 23) This is one of the two communities described from riparian mires. From the point of view of hydrology and species composition these communities are closely relat ed to the Restio Marshlands, hence they are classified as such in this study. These communities occur along the highest reaches of the rivers (in this study all were sam pled in the Palmiet River catchment) and have a mixture of seepage and riparian elements making up very species-rich communities, both in comparison with other seepage types as well as with riparian communities. The Erica autumnalis-Restio purpurascens community has a more prominent tall herb layer than most of the seepage communities. The dominant species is Restio purpuras cens, but Elegia racemosa and E. thyrsifera are also abundant. In the lower stratum. Anthochortus crinalis is conspicuous. Some species such as Hippia pilosa and Senecio crispus are shared with Community Group A. This type can best be described as a Restioland. because small and big restio species are its most important struc tural constituents. It is difficult to determine the differen tial species in a situation where relevés are few. but Aristea baker i, Cliffortia ova I is, Elegia racemosa. Hippia pilosa and an unidentified species of Asteraceae. might serve as possible candidates. Eponymous Erica autumnalis is endemic to the HHM. The community occurs in the highest reaches of the Wesselsgat River, where riverbanks are steep and rocky.

relevés 24-26)
This is the other type of riparian mire found along high altitude streams. The main difference from the pre vious type is the shape of the banks, which are tlatter and less rocky in this vegetation. The dominant small restio here is Restio aff. versatilis. compared with Antho chortus crinalis in community B2. This community has a tall herb stratum (reaching 1.0-1.5 m), dominated by the shrubs Berzelia squarrosa, Brunia alopecuroides and Grubbia rosmarinifolia and restioids Restio purpurascens and Chondropetalum mucronatum. The most closely related riparian commu nity is the Erico-Tetrarietum crassae (Sieben 2003), which shares many Erica species with the Grubbia ros marinifolia-Restio aff. versatilis Closed Shrubland. The most closely related seepage community is the Tetrario capillaceae-Restietum subtilis. A species that is shared with this community is Restio aff. versatilis. which is the dominating element of the ground layer. The Grubbia rosmarinifolia-Restio aff. versatilis Community is typi cal of situations where river banks are not steep and there is a lot of lateral seepage. It can be described as a shrub land because of the high cover of shrubs of Ericaceae and Bruniaceae. There are many differential species, most of which are shared with ericaceous fynbos and the Erico-Tetrarietum crassae in particular. These are. amongst others, Brunia alopecuroides. Berzelia squar rosa. Erica fastigiata, Grubbia rosmarinifolia and Restio bifidus.

Community B4: Tetraria capillacea-Restio subtilis
Short to Tall Closed Restioland ( This is the most common type of seepage community in the area, which can be characterized by the absence of Senecio crispus. The dominant restio is Restio subtilis, with Anthochortus crinalis and Restio aff. versatilis as co-dominants. A typical characteristic is the mosaic formed by patches of low vegetation of small restios and sedges (Restio subtilis, R. aff. versatilis. Tetraria capillacea and Epischoenus villosus) and patches of tall veg etation consisting only of Chondropetalum mucronatum. This species does not resprout after fires, like many other seepage species, but regenerates from seed. It tends to dominate the community, because the old plants form a thick litter layer on the soil beneath it. which seems to prohibit other (aggressively spreading) clonal species from growing there.
Differential species of this community are few. because most species are shared with the Grubbia ros marinifolia-Restio aff. versatilis Closed Shrubland. Diagnostic features are mostly the dominance of Restio subtilis and the occurrence of Chrysithrix species. As in the case of the riparian seepage types, this community contains numerous shrub species, such as the differential species Grubbia rosmarinifolia and Berzelia squarrosa. but they do not grow very tall.
This community occurs on more minerotrophic soils than the former communities. Nevertheless, the soils are very acidic and highly organic. In one case it was found in a riparian zone and it is closely related to the riparian seepage types described above. The community described by Boucher (1978) as Chondropetalum-Restio Tussock Marsh seems to be quite similar, but the domi nant small restio in the Kogelberg is not Restio subtilis but R ambiguus and many other species are absent in the Kogelberg community.

(Gradient analyses
The most important environmental factors that come out of the CCA (Figure 2) are slope and altitude. This is mainly due to the outlier communities of Al and A2. which are located at a higher altitude and on steeper slopes than any other of the mire communities. They also have, together with the riparian mire communities B2 and B3. the highest values for rockiness. It is interesting to see that there is a sharp contrast in the fraction of soil particle sizes: the fraction of coarse sand is an important environmental variable and the communities with a high fraction of coarse sand are the riparian mires (B2 and B3) o.
and restio marshlands (B4) which are the most minerotrophic mires in the mire system. On the other hand, there are the communities which have a high frac tion of fine sand and silt, which represent the fens in the middle of the mire system where peat formation occurs (especially A3, but also A4 and A5). The axis that is formed by the variable of coarse sand, fine sand and silt reflects a gradient in minerotrophy or in waterlogging. The fens (A3, A4 and A5) have the highest values for organic matter contents and soil depth. They are also mainly found at the higher altitudes because this is where the highest rainfall occurs.

DISCUSSION
One of the most important questions that is raised from the results of this study is where the high-altitude mires of the Fynbos Biome fit into the world-wide typol ogy of fens and mires. Although the mires regularly form the sources of the rivers, they are clearly very different from the European spring ecosystems (Zechmeister & Mucina 1994). Swamps and bogs with a high graminoid cover are found extensively in the boreal zone of the northern hemisphere (Sjors 1983) and the vegetation cover of swamps and bogs in Africa is also mostly domi nated by graminoids (Thompson & Hamilton 1983). Gore (1983) distinguishes between ombrotrophic and minerotrophic mires, based on the origin of the water. In ombrotrophic seepage, a thick layer of peat has devel oped and there is no more contact with the mineral sub strate. The water originates exclusively from rain, which results in very oligotrophic conditions. The water from minerotrophic mires seeps through the mineral substrate into the mire, so it is richer in nutrients than the om brotrophic mire. Ombrotrophic mires can only exist in very humid climates such as the blanket bogs of the British Isles and the elevated bogs of northern Europe; they are quite rare in the southern hemisphere. Actually, the distinction between ombrotrophic and minerotrophic mires is more like a gradient, an idea expressed by Sjors (1983). Ombrotrophic mires are on the one extreme of this gradient and all mires that do not feed exclusively on rainwater make up the rest of this gradient. Sjors (1983) also gives a more detailed subdivision of European mires: topogenous mires (influenced by stag nant water), soligenous mires (influenced by seepage), limnogenous mires (influenced by floodwaters) and ombrogenous mires (influenced by rainwater). Solige nous and limnogenous mires are both associated with rivers. Soligenous mires form around springs and lim nogenous mires occur in the floodplains along the lower reaches of rivers. The mires described in this study are all of the soligenous type. The different communities described in this study are situated along a gradient from dry to moist. In the Ficinio argyropae-Epischoenetum villosi Association, occurring in the centre of the mire, water stagnates more because the drainage is slow. On the edges, the Tetrario capillaceae-Restietum subtilis Association, which has a faster drainage, will prevail. Further towards the margins, communities dominated by Chondropetalum deustum can occur, but these were not recorded during this study. Two communities can occur towards the centre of very wet mires, namely the Anthochorto crinalis-Elegietum intermediae Association or the I sole pis prolifer-Bulbinella nutans Tall Closed Sedgeland described from the Du Toitskloof Mountains. Both communities are extremely poor in species, because of the specific stresses that occur under water logged conditions. It is clear that this gradient, from well-drained to poorly drained or from the edge to the centre of the mire, is also very prominent in the ordina tion diagrams. This gradient was also found by Bragazza & Gerdol (1999) in some mires in the southeastern Alps.
The other distinguishing feature that shows clearly in the ordination diagrams is the importance of the substrate, as can be seen from the Protea nmndii-Hippia pilosa Tall Shrubland from the shale band.
A conspicuous thing about the vegetation of mires of the Fynbos Biome is that they are dominated by the clon al restios A. crinalis, P. depauperatus and R. subtilis (Linder 1985). Because these species tend to cover everything, the vegetation is relatively poor in species. Clonal reproduction is often coupled to environmental plasticity, so the species can tolerate slight differences in the environment. The diversity of microsites is much bigger than the species richness suggests (Price & Marshall 1999). The tall restio C. mucronatum only regenerates from seed after fires and usually occurs in large, dense monotypic stands when mature. It does not support much vegetation underneath it. The dead mater ial from previous generations can form dense accumula tions of debris and this creates a very unfavourable sub strate for other species.
In marshes elsewhere in the world, clonal sedges and grasses take the place of the clonal Restionaceae record ed in this study. It is generally accepted that the clonal growth form is an adaptation to the stress of waterlog ging. This is confirmed by the investigations by Soukupová (1994) of three clonal graminoids. After waterlog ging there is an increase in clonal modules. Specht (1981) reviews many of the problems that sclerophyllous plants have to overcome in seasonally waterlogged areas.
It has become clear from this study that the mires in South Africa are very different from those in the northern hemisphere. Although they are vulnerable to predicted cli mate change (Rutherford et al. 1999). there is very little knowledge about the fens and mires of the southern hemi sphere. In order to be able to make general statements about mire ecosystems, more attention should be paid to the mire ecosystems in countries like South Africa.