Vegetation of the coastal fynbos and rocky headlands south of George , South Africa

Community structure and composition of the coastal fynbos and rocky headland plant communities south of George, southern Cape, were studied. Vegetation was analysed using standard sampling procedures of the floristic-sociological approach of Braun-Blanquet. The releve data were subject to TWIN SPAN-based divisive classification, and ordinated by Principal Coordinates Analysis with the aim to identify vegetation coenocline subsequently interpreted in terms of under­ lying environmental gradients. Most o f the sampled vegetation was classified as coastal fynbos. The Leucadendron salignum-Tetraria cuspidata Fynbos Community was found to occupy sheltered habitats, whereas the Relhania calycina-Passerina vulgaris Fynbos Community was found in exposed habitats The other two communities characterise strong­ ly exposed rocky headlands. The Pterocelastrus tricuspidatus-Ruschia tenella Community is wind-sheared scrub, and the Gazania rigensLimonium scabrum Rocky Headland Community is a loose-canopy, low-grown herbland, characterised by the occurrence o f partly salt-tolerant and succulent herbs. The ordination of the fynbos communities revealed a horseshoe structure allowing a direct recognition of a coenocline spanning two fynbos communities along the Axis 1 interpreted in terms of exposure to wind and salt spray. A considerable amount of alien plant infestation was also present. This appears to be the largest threat to the continued existence of this coastal fynbos.


INTRODUCTION
Fynbos occurring in close vicinity of the coast has been studied in detail in many regions of South Africa (Boucher 1977; Van der Merwe 1979;Cowling 1984;Taylor 1985;Hellstrom 1990;Taylor & Boucher 1993;Hoare 1994).There are, however, still many portions of the coastline, especially outside formal reserves, which remain only poorly known.Only 79 km of the central south coast falls into existing protected areas, namely the Goukamma Nature Reserve, the Robberg Nature Reserve and the Tsitsikamma Coastal National Park (Jarman 1986).The promulgation of the Agulhas National Park may alter these statistics (World Wide Fund for Nature 1999).
The area along the coast south of George, the present study area, is of interest because of its scenic beauty and its location in the centre of the popular Garden Route.Interest in coastal development for recreational purposes through out the Garden Route is likely to impact on areas which have not yet been encroached upon.The extent of vegeta tion cover outside formally protected areas has been con siderably transformed, and of the remaining natural areas large portions have been invaded by alien species.It was therefore suggested by Cape Nature Conservation (George) that a detailed study be undertaken along the coast south of George to provide information on the local vegetation and flora and possible importance of the study area for conser vation (G.Hellstrom pers. comm.).This particular study features descriptions of the plant communities of habitats close to the coastline.
The study area extended from Rooiklip, SE of Pacaltsdorp, to Ghwanobaai. 3 km E of Glentana (Figure 1), and covered ± 190 hectares.Glentana, and the area west of it, has been extensively developed and was therefore found unsuitable for the intended study.The fynbos vegeta tion in the study area has been classified as Asteraceous Fynbos by Cowling & Holmes (1992) and it was broadly classified by Acocks (1988) as 'cultivated land, plantations, dense alien communities and open sandy areas', a descrip tion which gives a clear indication of the transformed state of the vegetation.The vegetation of the coastline area is classified as Dune Thicket (Low & Rebelo 1996), which forms a mosaic with Dune Fynbos (Low & Rebelo 1996) in the region including the study area.
The coastline consists of steep coastal cliffs ranging in height from 50 to 70 metres, forming rocky headlands.The plenitude of alternating bays and headlands has resulted in microhabitats with varying degrees of expo sure to the prevailing winds, salt spray and sun.Coastal soils vary markedly according to substrate, but are often calcareous and coarse-grained.Topography is the domi nant factor affecting soil formation and the removal of the products of weathering may exceed their formation, especially on slopes.The coastal cliffs of the study area are Rooiklip Granite-Gneiss of the Kaaimans Group and are pre-Cape intrusive granite rocks (South African Committee for Stratigraphy 1980).These rocks are important because, upon weathering, they form base-rich substrates containing exchangeable cations that are important for soil formation and plant nutrient cycling (Deacon et al. 1992). of 8°C near the coast.The area has precipitation during all months of the year, with three prominent peaks in spring, summer and autumn, although there is no precipitation deficit at any time of the year (Figure 1).Sea mists may provide additional moisture on seaward-facing slopes.Pronounced strong winds blow along the entire coastal belt, varying in direction according to location and season.In the study area, wind from the southwest and west were found to be more important, since their frequency was higher (Weather Bureau 1994).Wind velocity has been found to be important in coastal plant communities, since the greater the velocity of the wind, the higher the salt load of the moving air, which may have a serious detrimental effect on the growth of plants (Avis & Lubke 1985).Importance values (Table 1) were determined which took into account the velocity and frequency of winds from dif ferent directions (IV = mean monthly direction frequency multiplied by mean monthly velocity expressed as per centage of total of all values for year).Westerly winds had the highest importance values throughout the year but were of greatest importance during the winter months.Southwesterlies showed a similar pattern.Easterlies and southeasterlies had the second highest importance values, but these were most prevalent during spring and summer (September to March).

MATERIAL AND METHODS
Aerial photographs were used to stratify the region into broad vegetation complexes based on vegetation structure and releves (25 m2 each) were made within these zones.The quadrat size was determined from species/area curves drawn from data collected in the study area, but also conformed to a scale-related approach to vegetation sampling, i.e. the size of the releve was related to the scale at which the vegetation was studied (Rutherford & Westfall 1994).Riparian thicket, dune thicket, dense alien stands and agricultural lands were not sampled.Standard field techniques and the 7-grade sampling scale of Braun-Blanquet (Westhoff & Van der Maarel 1973;Werger 1974) were used to record the cover/abundance values for each vascular species encountered in the releves.Topographic informa tion, including slope, aspect and altitude were also The vegetation data were initially classified using TWINSPAN (Hill 1979), producing a rough species-byreleve matrix, which was further rearranged in order to finely tune the releve/species coincidence patterns sup posed to carry meaningful ecological information.The data from only the fynbos communities were subject to ordination by Principal Coordinates Analysis based on similarity ratio as resemblance measure with no a priori data transformation using the programme package SYN TAX-5 (Podani 1993(Podani , 1994)).
For the descriptions of vegetation communities, three informal ranks of vegetation units are recognised: com munity, subcom m unity, and facies.Facies (Braun-Blanquet 1964) represents the lowest-ranked unit and corresponds to vegetation stands dominated by a single species, mostly an alien element.

Classification o f plant communities
The rearranged species-quadrat matrix (Table 2) revealed two groups of plant communities: the majority of the releves were classified as coastal fynbos (Com munities A & B) and the remainder of the releves as (non-fynbos) rocky headland communities (Communities C & D).A summary of the community environmental and floristic relationships is given in Figure 2. The following communities, subcommunities and facies were identified:

A. Leucadendron salignum-Syncarpha paniculata Fyn bos Community
This community occurs in areas that are protected from coastal winds either by headlands or the proximity of coastal thicket (Figure 3 Slopes vary from moderate to steep and soils are gen erally deeper and finer-grained than on cliff summits.There is high species richness (19 species on average) in this community.The habitat is more variable than on the cliff summits, thus leading to a greater species turnover between localities.The geographic distribution of this community beyond the present study area is unknown.Four subcommunities are recognised and described.

Ac. Typical Subcommunity
Lacks the diagnostic species of the other three sub communities, but contains the diagnostic species of the Leucadendron salignum-Syncarpha paniculata Fynbos Community.There was evidence of recent fires in a num ber of the releves.

Ad. Hermannia althaeifolia Subcommunity
Diagnostic species: Hermannia althaeifolia, Hibiscus aethiopicus, Ficinia albicans and Ursinia saxatilis as well as a number of infrequently occurring species (Table 2).Most of the releves had evidence of being burnt recently, suggesting that it is an early post-fire successional stage.
The vegetation height varies from 1 m, where dwarf shrubs are dominant, to over 2.5 m where shrubs of the exotic Leptospermum laevigatum are found.The mean species richness of this subcommunity is 20 species on average, but this may be reduced to only eight species where invasion by exotic shrubs has taken place, as is the case of the Acacia meamsii facies (Table 2, rel.23).

B. Relhania calycina-Phylica confusa Fynbos Com m u nity
This community makes up the greatest proportion of the fynbos in the study area and also extends beyond the boundaries of the present study area along the summit of the coastal cliffs towards Knysna (Figure 3).Diagnostic species: Relhania calycina subsp.calycina and Viscum capensis.Dominant species: Erica discolor, Phxlica con fusa.Passerina vulgaris and Tetraria cuspidata.Common species: Thesium virgatum, Agathosma ovata.Erica peltata.Syncarpha paniculata and Cliffortia serpyllifolia.
The dwarf shrub layer of this community is usually about 1 m in height and the herb layer about 0.4 m.The total cover of the vegetation is slightly lower than for

Pterocelastrus tricuspidatus-Ruschia tenella Coastal Scrub Community
Pterocelastrus tricuspidatus -s2   other fynbos com m unities in the study area, mostly due to an absence of a distinct restioid stratum.The commu nity is exposed to sun and wind and is consequently hot and dry.Com pounding this dryness, the soils are gener ally shallow and stony due to natural surface erosion at the summit of these cliffs.Slopes vary from flat to mod erate.The community tends to grade into thicket inland, often with a tall Passerina belt before the true thicket.
There is a high degree of invasion by Acacia cyclops (present in 78% o f releves), possibly causing habitat modification, which could ultimately lead to irreversible changes in species composition and vegetation struc ture.

Ba. Tetraria cuspidata Subcommunity
This subcommunity has the same dominant and com mon species as the Community itself, but with Viscum capense as a common species.It is usually found more inland of the other subcommunity suggesting that the two subcommunities form a gradient from lower altitude to wind-protected inland plant communities.

Bb. Eriocephalus africanus Subcommunity
Transition to lower altitude, steep-slope communities.It has slightly steeper slopes than the typical cliff summit community and is often moderately exposed to the influ ence of salt spray.There are also higher soil conductivi ty levels, which can be attributed to higher levels of wind-borne salt effects (see below).Pterocelastrus tricuspidatus and Lampranthus socioruin are occasionally pre sent.This community is further marked by the absence of: Tetraria cuspidata, Viscum capense and Syncarpha paniculata.

C. Pterocelastrus tricuspidatus-Ruschia tenella Coastal Scrub Community
The woody component of this community reflects the species composition of the coastal scrub in the deeply incised valleys along this coastline and there is possibly a floristic gradient from this community into thicket on other steep slopes.Diagnostic species: Pterocelastrus tricuspidatus as well as infrequent occurrence of Sideroxylon inerme, Delosperma edwardsiae and Cineraria hritteniae.

D. Gazania rigens-Limonium scabrum Rocky Headland Community
Salt-tolerant asteraceous Gazania rigens var.uniflora and a taxon from the Limonium scabrum complex ac companied by mesembs such as Drosanthemum mari num and Ruschia tenella, as well as other leaf succulents such as Crassula sp. and Sarcocaulon natalense, form an assemblage typical of the exposed rocky headlands in the southern Cape.
Community C and the rocky headland 'herbland' Community D have many species in common, which can be ascribed to a so-called neighbourhood effect (or mass effect; Shmida & Wilson 1985).Naturally, the exposed Community D is virtually lacking (except of Sarco caulon natalense) in its 'ow n' diagnostic species because of the environmental stress in the form of deposition of wind-borne salt that poses a major selective pressure on the potential species pool.
Due to the low altitude this community is greatly exposed to the influence of the wind and especially to salt spray (Figure 3).The vegetation has a very low cover and is wind-cropped.The average height of the vegeta tion is between 0.13 and 0.33 m.O f all the community types, this one is lowest in species richness with a mean of 10 species on average.Shallow soil covering granite rocks is characteristic, and is often less than 5 cm deep and very stony.Surface boulders are often present and modify the microhabitat to some degree.A facies with Gazania rigens var.uniflora was distinguished within this community (Table 2, rel.68).This species com position corresponds with the description of similar rocky headland communities described for other parts of the coastline at Plettenberg Bay (Hellstrom 1990) and Port Alfred (Lubke 1983).

Gradient analysis
The ordination of the fynbos communities (Figure 4) revealed a horseshoe structure allowing the direct recog nition of a coenocline spanning two fynbos communities AXIS 1 along Axis 1 of the scatter diagram.There was a clear separation along this coenocline between the Relhania calycina-Phylica confusa Fynbos Community and the Leucadendron salignum -Tetraria cuspidata Fynbos Community.This pattern is interpreted in terms of expo sure to wind and salt spray as reflected in topographical features and soil properties.
A classification scheme accompanied by associated environmental relationships (Figure 2) suggests that the Leucadendron salignuni-Tetraria cuspidata Fynbos Community occurs on deep soils inland of the cliff sum mits where the vegetation is protected from wind and salt spray.The Relhania calycina-Passerina vulgaris Fynbos Community occurs on shallow, stony soils on the cliff summits, where there is a higher exposure to wind and salt spray.
Physical soil properties varied from community to community (Table 3).Cliff summits had the highest pro portion of coarse sand, slopes above the cliff summits had the highest proportion of silt, and steep tallus slopes and rocky headland slopes had the highest proportions of medium sand, fine sand and clay.This is a trend in decreasing sand particle size away from the cliff summit (below and above) and larger proportion of clay to silt below the cliff summits (steep tallus slopes and rocky headland slopes).
Soil conductivity levels showed a decreasing trend as exposure to wind from the sea decreased.High levels were recorded on the steep tallus slopes, the cliff sum mits and the rocky headland slopes.The two cliff summit communities showed a difference in conductivity levels with the Eriocephalus africanus Subcommunity having higher conductivity measures than the Tetraria cuspida ta Subcommunity.These higher conductivity levels were attributed to higher salinity levels from wind-borne salt spray effects.
Fire appeared to play an important role in the nature of the communities especially in the Leucadendron salignum-Syncarpha paniculata Fynbos Community where the subcommunities Aa and Ab could be separat ed from the subcommunities Ac and Ad based on evi dence o f recent burning.We suggest that the subcommu nities are distributed along a fire-induced succession gra dient, but with site-specific effects also coming into play.
FIGURE 1.-Map of the study area and climate diagram for George.
) and has a different species composition to the fynbos on the exposed summit of the coastal cliffs.Diagnostic species: Leucadendron salignum, Aspalathus asparagoides, Hermannia angularis, Metalasia acuta, Helichrysum cymosum and Bobartia aphylla.Dominant species: Syncarpha paniculata and Passerina vulgaris.Common species: Tetraria cuspidata.Cliffortia falcata, Metalasia pungens, Lobelia tomentosa.Erica discolor and Phylica confusa.Many stands of this community have been seriously invaded by the alien species Acacia cyclops, Leptospermum laevigatum and Pin us spp.
Subcommunity D iagnostic species: Thamnochortus cinereus, Polygala microlopha and Cliffortia sp. ( Victor 313).It is situated below a housing development at H erold's Bay Extension; there was no evidence of recent fire and the subcommunity is possibly one form of a fire-climax veg etation in protected areas.Ab.Protea neriifolia Subcommunity Diagnostic species: Protea neriifolia.It has developed in the absence of fire and is possibly a fire-climax vege tation of protected areas.Bobartia aphylla and Pelar gonium fruticosum serve as common linking species to subcommunites Aa and Ab.

TABLE 2 .-Classification o f the vegetation o f the coastal cliff habitats south o f George, South Africa (co n t) Bothalia 30,1 (2000)
Infrequently occurring spp.(sp.name; vegetation layer; releve n u m b e rs), cover/abundance score) Flat to moderately sloping regions Steep, sea-facing, rocky headland slopes Deep soils; inland of cliff summits, Com m unity environm ental and floristic relationships in the coastal fynbos between Rooiklip and Ghwanobaai, south of Geoig;e, South Africa.