Phytogeography of fynbos

Previous classifications of the vegetation of the Cape Floristic Region, or Capensis, are outlined. The distinctive features of the Cape flora such as species diversity, endemism and distribution patterns are discussed in an attempt to elucidate the origins and evolution of the principal vegetation type of the region, known today as fynbos. Evidence suggests that the present species-rich Cape flora has mainly evolved in and radiated from the southwestern part of Capensis, an area where a true mediterranean-type climate is found.


INTRODUCTION
In recent w orks b o th T a k h ta ja n (1969) and G ood (1974) allocated the ra n k o f K ingdom to the C ape flora despite its sm all area on a w orld scale, thus according it equivalent phytogeographical im portance to such vast regions as the H olarctic K ingdom which encom passes the whole o f the tem perate and arctic n o rth ern hem isphere.
The C ape Floral K ingdom is concentrated in the region know n to d ay as C apensis, the C ape foldedm ountain belt, th a t com prises the distinctive tem perate floral area o f the southw estern and southern C ape Province occurring betw een latitudes 31° and 35° south and longitudes betw een 18° and 27° east.The western p a rt has a distinctly m editerranean-type clim ate w ith dry sum m ers and wet w inters b u t east w ard the rainfall becom es increasingly non-seasonal.O ver the area as a whole, rainfall varies from extrem es o f 300 to 3 000 mm.
C apensis is bounded to th e west and so u th by the coast and to n o rth and east principally by the K aro o -N am ib Region (W erger, 1978a) together w ith som e outliers o f the Sudano-Z am bezian (W erger & C oetzee, 1978) and A from ontane Regions (W hite, 1978).The K aroo-N am ib flora penetrates into C apensis in the Little K aroo, an arid area betw een the coastal and inland m ountains (W erger, 1978a).O n m o u n tain s in the K nysna region C apensis intergrades w ith the A fro m ontane flora, and several C ape species such as Berzelia intermedia, D iospyros glabra, Leucadendron eucalyptifolium and Protea cynaroides becom e d o m i n an t as one ascends from foothill forest to M o u n tain F ynbos (W hite, 1978).
The F rom the tu rn o f the century, resident botanists like Bolus (1886Bolus ( , 1905Bolus ( ) and M arloth (1906Bolus ( , 1908) ) began to describe and m ap the vegetation o f South Africa.F ynbos delineation was gradually refined by Bews (1916), Pole Evans (1936), A dam son (1938a) and others, until finally A cocks (1953) in his wellknown m ap th a t is still in use today, recognized the three fynbos types m entioned above.In his discussion o f these and later w orks, W erger (1978b) concludes th at reasonable unity o f opinion on the zoogeographical boundaries in A frica was reached m uch earlier than was the case w ith phytogeographical boundaries.The latter are, indeed, still being debated (e.g.A xelrod & Raven, 1978) and a clear picture will only emerge when the taxonom y and distribution o f present floras, including low er p lan t groups, are know n in detail.

CHARACTERISTICS A N D AFFINITIES
The singular biogeographic features th a t led phytogeographers to give the C ape flora such a high status in their classifications include the great concen tration o f species, the high degree o f endem ism , the characteristic d istrib u tio n patterns o f typical elem ents despite a general lack o f species dom inance, and the predom inance o f certain fam ilies and genera.The C ape flora " is noted for its richness in species, both in small areas and over its w hole range" (Taylor, 1978), and has been claim ed as being one o f the richest in the w orld for its size (Oliver, 1977).F o r diversity at the com m unity level (alpha diversity), Taylor (1972) 1938b), b u t also interm ittently along the eastern highlands o f the continent as far n o rth as central A frica (Oliver, 1977).M any other typical Cape taxa have sim ilar distribution patterns.In fact there are so m any in the D rakensberg th a t b o th K illick (1963,1978) and E dw ards (1967) have described a type o f " fynbos" for th a t area, and Boughey (1957Boughey ( ), H edberg (1965) ) and W ild (1968) have recognized a " C ape elem ent" on the m ountains o f R hodesia and East Africa.But the floras o f high m ountains in southern and central A frica are incom pletely know n and inten sive plan t collecting is needed to provide d ata fo r a full phytogeographic study o f these interesting m igration routes.
Fam ilies th a t are richest in genera a t the C ape b u t widely distributed in other parts o f the w orld include Fabaceae, Iridaceae, Rosaceae and Thym elaeaceae.In contrast, m any taxa o f high ran k are endem ic to the Capensis region or nearly so.These include Bruniaceae, Penaeaceae, Stilbaceae, G rubbiaceae, R oridulaceae and G eissolom ataceae, the tribe D iosm ae o f the R utaceae and large genera such as Aspalathus, Phylica, M uraltia and Cliffortia (Oliver, 1977;Axelrod & Raven, 1978;T aylor, 1978).Weim arck (1941) found th a t o f 282 genera w ith their centre of origin in Capensis, 212 were endem ic, and he estim ated th a t m ore th an 3 500 species were endem ic out o f the to tal o f 4 200 th a t he surveyed.In exam ining local endem ism , W eim arck found th a t the two w esternm ost centres together contained 4 5 ,5 percent o f the total num ber o f endem ics represented within the " Cape p ro p er." Taxonom ic studies show th a t both palaeo-endem ics, or relics, and neo-endem ics, or recently evolved species th at are still lim ited to a sm all area, occur in the Cape flora.These types have local or disjunct distributions or both.The Proteaceous species Orothamnus zeyheri, M im etes hottentoticus and Leucadendron argenteum are, by virtue o f th eir distribution and biology, considered to be palaeoendemics.R ourke (1972) reports vicariad groups o f neo-endemic Leucospermum species on coastal low lands of the southern Cape and Levyns (1954) shows th at several M uraltia species occupying the same coastal strip are also youthful endem ics.F rom phylogenetic evidence, Oliver (1977) considers some species in the m inor genera o f the Ericaceae, and even some o f the genera themselves, to be neo-endem ic.M arloth (1929) and G o ld b latt (1972), am ong others, have attributed this local endem ism and disjunction partly to the diverse topography o f the region, in which the concom itant diversity o f soils and local climates, and the appearance o f new land surfaces along the coast, gave opportunities fo r recent speciation, and partly to the great age o f the flora, m em bers of which may have been able to survive clim atic changes by retreating into favourable localities.
W eim arck (1941), Levyns (1938Levyns ( , 1952)), D ahlgren (1963), W illiams (1972) and others have show n th a t typical families and genera o f the C ape flora have a characteristic distribution pattern in which the highest num bers o f species per area are concentrated in the western p art o f the region (see Fig. 1).Levyns (1952) went so far as to state it as a " rule th a t all genera o f the Cape F lora show a concentration in the south- In contrast, certain au stral forest elem ents th a t also do n o t have the typical southw estern co n cen tratio n occur w ithin C apensis only as relic patches o f forest vegetation in m oist o r sheltered h ab itats and n o t as constituents o f fynbos.Such genera as Podocarpus, Cunonia, Platylophus and Curtisia are exam ples o f these (Levyns, 1962).T hough their presence suggests a previous w ider d istrib u tio n o f forest, there is little evidence th a t they are becom ing a d ap ted to the typical rigo ro u s h ab itats occupied by fynbos.
The C ape flora also co n tain s elem ents th a t are found m ore com m only in m ore d ista n t lands.The grass Hyparrhenia hirta has a wide b u t d isjunct d istrib u tio n in the coastal M ed iterran ean , in east A frica and in southern A frica, linked only by high m o u n tain outliers in the S ah ara (Q uézel, 1978).G enera such as Anem one, Rubus, Scabiosa, Geranium and Dianthus have their m ain centres o f co n cen tratio n in the n o rth ern hem isphere.Aloe, Euphorbia and the A sclepiadaceae are p ro m in en t m em bers o f o th er A frican floras.Gladiolus is w idespread elsew here in A frica and beyond.Rhus and Euclea have m any m ore species in subtropical forest, scrub an d savanna th a n in fynbos (T aylor, 1978).Sim ilarities a t the generic level suggest com paratively recent m igrations and interm ingling.Sim ilarities at a higher tax o n o m ic level suggest older affinities.A d am so n ( 1958 A picture em erges from this acco u n t o f a present flora with high alp h a an d g am m a diversities, a flora uniquely characterized by three w idespread fam ilies and som e endem ic ones, and by m any endem ic tax a o f lower rank, som e young, som e old, som e w idespread w ithin the region, som e restricted o r disjunct in distribution.T he flora has a high concentration of species in the west, it shows som e close taxonom ic affinities w ith ab u ttin g floras and w ith the central African m ountain flora, obvious b ut m ore distant affinities with the flora o f southw estern A ustralia, and tenuous relationships with n o rthern hem isphere floras.In all, the Cape flora is floristically and phytogeographically unique.D espite m igrations and interminglings, it appears to have been isolated for a long tim e and to have suffered vicissitudes th a t have encouraged speciation, radiation and hybridization at a singularly high rate.

ORIGINS A N D EVOLUTION OF FYNBOS
Such features suggest a long and varied history of geology and clim ate.On these grounds and because dom inance by one o r m ore species is a rare p h en o m enon in m ature fynbos, the flora has h ith erto been generally regarded as an ancient one (M arlo th , 1915;Bews, 1925;W eim arck, 1941;Levyns, 1952;A dam son, 1958;D yer, 1966).Y et despite general agreem ent on its age, there has been m uch controversy a b o u t the origin o f the C ape flora.O ne school postulated an origin in the n o rth ern hem isphere, an o th er in the southern, while yet a third contended th a t it originated som ewhere in central A frica.
U ntil very recently the third theory has seemed m ost plausible, m ainly as a result o f the perceptive w ork o f Levyns (1938,1952,1958,1964), sum m arized by Van V uuren (1973).She pointed o u t th a t very m any m em bers o f the Cape flora, th ough they are concentrated in the Capensis region, show clear traces scattered th ro u g h o u t Africa, m ainly on m oun tains as far n o rth as Ethiopia.Proceeding southw ards these " islands" becom e m ore frequent until, south o f the Sw artberg, all the scattered m ountains o f the Little K aro o have cappings o f C ape plants while the flora o f the low lands is entirely different (Levyns, 1950).Levyns show ed, too, th a t the m ore prim itive m em bers o f C ape plants in m any groups are to be found in m o u n tain outliers w ithin the tropics, whereas in the southw estern C ape m any o f the species are advanced and occupy restricted geographical ranges.These d istrib u tio n patterns suggest th a t a flora o f the Cape type was once w idespread in central Africa, and th a t this flora retreated southw ard when the clim ate becam e unfavourable in the no rth , leaving traces on the no rth ern m ountains and speciating in the fav o u r able tem perate conditions found in the southw estern Cape.
This subject has been recently reviewed by T aylor (1978) w ho q u oted fu rther evidence suggesting th at the presum ed central A frican origin in fact represented a secondary centre o f establishm ent for a flora th a t originated in au stral lands.A review by A xelrod and Raven (1978), which appeared at the same tim e as T aylor's, presents evidence to su p p o rt this theory.The evidence strongly suggests th a t the sum m er-dry clim ate is o f recent origin in southern A frica and probably only appeared at the beginning o f the Pleistocene som e 2 ,5 million years ago.But already in the early M iocene, rapid speciation probably took place in S outh A frica with the broad w arping and uplift o f the continent.F u rth er study o f fossil floras li ^e those o f C oetzee (1978a, b) is needed to sub stantiate this.A t ab o u t this tim e increasing glaciation in A ntarctica b ro u g h t the cold w ater o f the Benguela C urrent to the west coast, accentuating the trend to increased sum m er d ro u g h t on the western land surfaces.T hen, when strengthening high pressure systems b ro u g h t this drier clim ate to the interior, sclerophyllous taxa th a t had lived earlier under sum m er and w inter rain were adapting to increasingly dry sum m ers.W ith dry sum m ers spreading from the west, the tax a th a t required sum m er rain were gradually restricted eastw ard.This left the western environm ent open for the sclerophylls w ith tolerance to w ithstand sum m er drought, and m any o f those th a t survived in this new h ab itat had great o p p o r tunities for evolutionary radiation.This supports the findings o f Levyns and others, m entioned earlier, th a t typical m em bers o f the C ape flora show a concen tratio n o f taxa and o f endem ics in the west.
But n o t all fynbos species originated in th eir present area.A xelrod & Raven (1978) postulate th a t even durin g the m ost recent clim atic changes in the Pleistocene, fynbos in its present area m ay have been restricted by the expansion o f forest and oth er vegetation, and could then have been displaced to the n o rth , into the regions now occupied by desert and sem i-desert.A t the end o f the T ertiary when the area o f dry clim ate expanded, fynbos w ould have retreated to its present area and, during this retreat, interchange between fynbos and isolated pockets o f relic sclerophyll vegetation may have co n trib u ted directly and through hybridization to the overall diversity o f the flora.Thus, the rich flora o f the present Capensis region " may represent b ut a rem n an t o f a m uch richer sclerophyllous flora th a t ranged over the present desert and steppe areas into the Pleistocene" (ibid., 1978).
T hough A xelrod and R aven's hypothesis is a ttra c tive, the diversity and high rate o f speciation in fynbos m ay n o t simply be the result o f mass p lant m igrations follow ing clim atic change.As Levyns (1963) has pointed out, a vegetation category, like fynbos, is n o t " a flock o f sheep" b u t an association o f taxa th a t extend and dim inish their ranges, n o t collectively b u t individually, in response to different factors to w hich the taxa are variously adapted.F o r exam ple, the fact th at fynbos is largely restricted to nu trien t-p o o r soils w ould preclude its m ovem ent en bloc in to the K aro o -N am aq u alan d area, even though individual taxa m ay a d a p t to the richer soils there.
The pulse o f alternating cooler and w arm er, and at tim es w etter, climates during the Q uaternary would also have contributed to the high diversity in the C ape flora.A t times o f m oister clim ate, some taxa o f the sclerophyllous C ape flora could have spread widely over the present K aro o region and speciated there." As drier clim ate returned, the flora shifted coastw ard into its present area, bringing new tax a w ith them and leaving relic stands in m oist situ atio n s" (Axelrod & Raven, 1978, p .116).Thus, even during recent clim atic changes in the Q uaternary, the C ape flora may have been far m ore w idespread (Levyns, 1938in Axelrod & Raven, 1978), and has only been restricted to its present environm ent for a relatively short time.
An interesting feature in su p p o rt o f this view is th a t some C ape plants enter into a period o f rapid vegetative grow th tow ards the end o f sum m er at a tim e when w ater supplies in the southw estern C ape are at their lowest.This strangely ill-adapted grow th rhythm suggests th a t the ancestors o f these plants " evolved in som e place having a sum m er rainfall.The sam e phenom enon has been recorded for South A ustralia, where a sim ilar change in clim ate is postulated to account for the same, apparently inexplicable, features o f grow th" (Levyns, 1964).This suggests th a t the m editerranean clim ate is not ancient, b u t is so youthful th a t the plants have not yet fully ad apted to it.F u rth er research on South A frican plants is needed to clarify this phenom enon.
As stated earlier, a true m editerranean clim ate is present only in the western p a rt o f Capensis.It is this western part th a t was first colonized by prim itive sclerophylls, and in the southw estern corner which has the highest rainfall and m ost diverse topography, speciation has been m ost active, producing the greatest concentration of taxa and endemics.This rich so uth western centre can be regarded as the true hom e o f the Cape flora from whence it has radiated.T o the n o rth its spread is limited beyond V anrhynsdorp by an arid climate, but eastw ard along the well-w atered south coast it extends into the regions o f non-seasonal and sum m er rain as far as G raham stow n.T he eastern extension, having relatively low diversity and few endemics, is presum ably younger th an the w estern part.Fynbos would probably only have started colonizing this eastern area when the coastal tem perate forest was reduced by a drying clim ate (cf.Acocks, 1975, M aps 1 & 2), b u t it has expanded its range faster within historic times owing to the destruction o f forest by man (Von Breitenbach, 1972), and veld m ism anagem ent is now encouraging its spread further eastw ard into m ountain grassland (T rollope & Booysen, 1971).
vegetation o f C apensis consists principally o f fynbos, a broad category o f diverse evergreen sclerophyllous shrublands com prising A cocks's (1975) veld types 47 (C oastal M acchia), 69 (M acchia) and 70 (False M acchia), b u t includes tw o tran sitio n al veld types, C oastal R enosterbosveld and Strandveld, th a t contain a m ixture o f C ape and o th er floristic elem ents.The b road p hytogeographic dem arcation o f C apensis began in the last century when b o tanical travellers included " the region o f the C ape flo ra " in their descriptions o f vegetation fo rm atio n s and floristic * Botanical Research Unit, P.O.Box 471, Stellenbosch, 7600.kingdom s.A m ong these pioneers were Schouw (1823), Drêge & M eyer (1843), G risebach (1872), R ehm ann (1880), Engler (1882), D rude (1887, 1890) and Schim per (1898).T heir vegetation descriptions and m aps, based on scant inform ation, were largely conjectural, and are o f mere historical interest today.

Map 3 .
Concentration of Aspalathus species.The figures express the number of species represented in the area of each square.The map is based on dot maps of all the species.The distribution in Natal and the Khamiesberg area are excluded (cf.map 1).It is seen that the squares with the greatest concentration of species cover the mountain regions in the southwest.The number in the square covering most of the Cape Peninsula is surprisingly high considering the area occupied by the Cape Flats, which are poorer in species, and the sea.A high number of species is found in all the squares covering the western and southern mountain ranges.The great contrast between the relative richness in the Witteberg-Zwartberg mountains and the poverty of species in the Little Karroo deserts has only partly been possible to demonstrate.F ig .1.-M ap 3 from Dahlgren (1963).west.A ny a p p aren t co n stitu en t, w hich does n o t show this p articu lar p attern o f d istrib u tio n , m ay be sus pected o f being an in v ad er."The R estionaceae, Proteaceae and m ost o f the Ericaceae show this p attern, as do the endem ic fam ilies Bruniaceae and Penaeaceae and the larger genera Cliffortia, Aspalathus, Phylica, M uraltia and Leucadendron.O n the o th er han d , genera like Babiana, Ferraria and Pteronia th at are fairly com m on in C apensis have their m axim um co n cen tratio n in N am aq u alan d .A m ong o th er " a p p a re n t co n stitu e n ts" th a t do n o t show the typical southw estern d istrib u tio n are species o f Aloe, Erepsia, Carpobrotus, Crassula and Zygophyllum.The presence o f such species w ithin the C ape flora and the presence o f fynbos outliers on high m ountains in N am aq u alan d as far n o rth as S pringbok suggest an interm ingling o f the C ape flora w ith those floras ab u ttin g it to the n o rth .
) considered th a t pairs o f taxa like Selaginaceae (C ape) and Globulariaceae (M ed iterran ean ), Dim orphotheca and Calendula, Lobostem on and Echium , Crassula and Sedum , and W iddringtonia an d Tetraclinis provided evidence o f a once w idespread flora th a t becam e fragm ented as the clim ate changed an d th en evolved in isolation.The affinity o f the C ape flora w ith th a t o f so u th w estern A ustralia is striking b u t m ore rem ote th a n its affinities w ith n o rth ern hem isphere floras.The Thym elaeaceae, H aem o d o raceae an d D roseraceae are com m on to b oth con tin en ts an d the endem ic C ape fam ily R oridulaceae is closely paralleled by the A ustralian Biblidaceae.D iosm ae (R utaceae) o f the C ape has its c o u n te rp a rt in the A u stralian tribe B oroniae (Bolus & W olley-D od, 1904) and the genera Tetraria and Gahnia, and Phylica an d Cryptandra are closely related (A dam son, 1958).
All three families have strong concentrations o f taxa in Capensis.O utliers occur on m ountains not only in adjacent dry areas to the n o rth , especially N am aqualand (A dam son,