Late Quaternary Palaeoenvironments of the southwestern Cape, South Africa: a regional synthesis

Quaternary International 57/58 (1999) 193}206

Late Quaternary Palaeoenvironments of the southwestern Cape, South Africa: a regional synthesis Michael E. Meadows*, Andrew J. Baxter Department of Environmental & Geographical Science, University of Cape Town, Rondebosch 7700, South Africa

Abstract The contemporary uniqueness of the southwestern Cape environment suggests that its response to the environmental perturbations of the late Quaternary may have been correspondingly distinctive. Despite the wide variety of palaeoenvironmental evidence which has accumulated from within the region, a coherent picture of the evolution and development of its environments has remained elusive. Since the publication of several regional reviews over the last decade or so, a considerable body of palynological and other palaeoecological evidence has emerged which prompts a fresh synthesis as to the nature of late Quaternary environmental changes in the southwestern Cape's fynbos biome. Although there are few sediments which date to the appropriate period, the last glacial maximum, in contrast to the situation evident in the summer rainfall region, is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome. The "rst half of the Holocene appears to have been somewhat drier than much of the second half and the warmer temperatures of the Holocene hypsithermal are associated with reduced moisture availability. Intra-regional contrasts are evident in the response to late Quaternary environmental changes. Furthermore, it transpires that, for much of the later Quaternary and for large areas of the region, precipitation may have #uctuated out of phase with changes in the interior of the subcontinent, a situation which has great relevance to the prediction of future environmental changes and their impacts in the southwestern Cape.  1999 INQUA/Elsevier Science Ltd. All rights reserved.

1. Introduction: unsolved problems in Quaternary studies of the southwestern Cape The growth of studies of the Quaternary period in southern Africa has been fueled by the recognition that an understanding of environmental changes of the past is an important key to making more accurate predictions as to the nature of environments of the future. There has been a marked expansion in the number of palaeoenvironmental reconstructions in southern Africa, particularly those involving the late Quaternary. These reconstructions are based on an increasingly wide range of types of evidence. Patterns of late Quaternary environmental change in the sub-continent are beginning to emerge, as witnessed by the review of Partridge et al. (1990), and it is clear that di!erent regions within southern Africa have responded uniquely to the global changes that have characterised the last 20,000 yr or so of earth

*Correspondence author. Tel.: (27) 21 650 2877; fax: (27) 21 650 3791; e-mail: [email protected].

history. The time is once again appropriate to re#ect on the body of evidence on #uctuating environments which has accumulated in di!erent regions of the sub-continent. This paper examines the evidence for late Quaternary environmental change in the southwestern Cape region (Fig. 1), a part of South Africa which is subject to mainly winter rainfall and which is associated with the unique and proli"cally biodiverse plant communities known collectively as fynbos (see Cowling et al., 1992). The term southwestern Cape is taken as broadly speaking synonymous with the area of winter rainfall as de"ned by Meadows (1997) and approximates ®ion A' of Partridge et al. (1990) and also the area occupied by the fynbos biome (Cowling et al., 1992). An examination of the literature pertaining to the southwestern Cape (see below for references) reveals that there remain a number of outstanding questions regarding the nature and signi"cance of environmental change during the Quaternary period. The most fundamental questions surround the characteristics of the climate in the southwestern Cape, broadly-speaking corresponding to the area occupied by the fynbos biome (Cowling,

1040-6182/99/$20.00  1999 INQUA/Elsevier Science Ltd. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 9 8 ) 0 0 0 6 0 - 3

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Fig. 1. Location of sites mentioned in the text and showing the southwestern Cape winter rainfall region as de"ned in Meadows (1997).

1992), during the period spanning the last glacial maximum through to the present day, viz., (a) What are the most important characteristics of the regional climate of the late Quaternary insofar as it has responded to major global changes? (b) Has the region reacted in a spatially and chronologically consistent manner to late Quaternary environmental change or are sub-regional variations apparent? (c) How will the region respond to climatic changes of the future, for example, what will the regional response be to assumed global warming? That such questions still abound prompts the need for a southwestern Cape regional review of the late Quaternary evidence for environmental change. This is achieved through, "rstly, a brief synopsis of contemporary environmental characteristics. Secondly, previous attempts at synthesising the Quaternary palaeoenvironmental evidence of the region are considered. Thirdly, a fresh synthesis is constructed employing both recently published and thus far unpublished evidence. Finally, the questions outlined above are revisited with a view to establishing the bio-physical signi"cance of past, and possible future, environmental changes in the southwestern Cape. 2. Contemporary natural environments of the southwestern Cape Considerable complexity is evident in the natural environment of the contemporary southwestern Cape and

any reliably accurate reconstruction of Quaternary palaeoenvironments must take this into account. Indeed, it could be hypothesised that, since it is clear that prevailing environmental conditions vary markedly with geographical locality, any identi"ed palaeoenvironmental changes should be spatially variable. In short, since environmental and biogeographical gradients in the region are steep, there is no reason to expect environmental changes of the Quaternary to have been either contemporaneous or unidirectional across the region. At the southwestern tip of Africa, a mediterraneantype climate, coupled with a particular combination of geology, topography, soils and environmental and cultural history, has resulted in a distinctive landscape characterised by a unique vegetation formation. Perhaps more than any other feature of the natural environment, this highly species-rich vegetation type, known as fynbos, is what distinguishes the southwestern Cape from other regions in southern Africa, indeed from other regions of mediterranean-type climate. Its diversity, in terms of numbers of plant genera and species, rivals even that of the tropical rain forests (see Cowling et al., 1992) and suggests that the long-term evolution and development of the southwestern Cape environment has followed a distinctive and complex course. In many ways, this region represents an &island' at the southwestern corner of Africa, isolated by a series of folded mountain ranges trending parallel to the coast. A rich variety of vegetation communities is associated with the #ora, although structurally there is a measure of

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uniformity in that most of these may be described as sclerophyllous shrublands which, in this sense, are typical of other mediterranean-climate regions. Indeed, much has been made of the issue of convergent evolution in the "ve regions with this climate type; Cody and Mooney (1978) have concluded that, in terms of structure and physiognomy, the communities of the Mediterranean basin, California, Chile, southwestern Australia and southwestern South Africa are strikingly similar. All areas are dominated by evergreen shrubs, frequently dwarf in character, with sclerophyllous leaves. The socalled fynbos communities of the southwestern Cape are no exception; typical fynbos vegetation types prevail across much of the region, although they occur in a mosaic with other, non-fynbos, plant communities. The fynbos biome consists of several phytogeographically and ecologically distinctive groups of plant communities which occur in relation to particular combinations of climate, substrate, topography and "re frequency, although it seems that human activities determine the survival, or otherwise, of many of these communities in the present day. The most remarkable feature of the #ora is its species richness and degree of endemism (Cowling et al., 1992) and it has one of the highest species densities and numbers of endemics for any temperate or tropical continental region (Cowling et al., 1992). The mechanisms underlying this legendary diversity are complex and not well understood, although the nutrient-de"cient soils acting in concert with the roles of "re and biogeographical history would appear to be centrally involved (Linder et al., 1992). Taxa indicative of the #oristic region include numerous members of the Restionaceae, Proteaceae and Ericaceae families, although there are many other families and genera which may be regarded as &typical'. Several plant families are especially diversi"ed in this #ora, in particular the Ericaceae, Asteraceae and Orchidaceae. Single-species dominance is unusual and it is, perhaps, the variety of di!erent species and their spatial distribution which best characterises the vegetation. The most obvious environmental relationships are found between underlying geological parent material and vegetation. Oligotrophic soils on uplands derived from the Table Mountain Group sandstones, together with soils developed on the granites, support mainly mountain fynbos vegetation. Typically a shrubland, the vegetation is characterised by ericoid, proteoid and restioid leaf forms (ie plants which, while not necessarily belonging to the Ericaceae, Proteaceae and Restionaceae families, share their characteristic leaf-forms and physiognomy. Calcareous dunes at the coast support a xerophytic community known as strandveld, which may be regarded as transitional between true fynbos and the karroid communities of the drier interior. Here, the ericoid and proteoid elements are less abundant and the vegetation is more succulent in nature. Renosterveld, strictly-speaking a non-

195

fynbos community, is dominated by Elytropappus rhinocerotis, is associated with the more nutrient-rich shales of the Malmesbury Group, although there is so little of it remaining because of the relative fertility of the soils which has seen them much utilised for wheat farming. Another non-fynbos community is Afromontane forest, mainly found on southeasterly-facing slopes and &kloofs' (ravines) on sandstones of the mountains and coastal uplands. The distribution of all these plant communities in the region has been markedly a!ected by human activity, although the degree of ecosystem transformation, which has an extended history because the southwestern Cape has been occupied for much of the late Quaternary, varies according to the characteristics of the vegetation type in question. For example, the renosterveld communities have all but been completely consumed by the growth of agriculture, particularly wheat farming, whereas the mountain fynbos remains relatively una!ected by this form of land use and is, instead, modi"ed by management adjustments in the "re regime and the spread of alien invasive plants (Meadows, 1997). Having reviewed the contemporary environmental situation in the region, it is now appropriate to examine previously published syntheses of Quaternary palaeoenvironments.

3. Previous late Quaternary environmental syntheses of the fynbos biome Three major Quaternary environmental syntheses have been attempted since 1980, viz., Deacon et al. (1983), Deacon and Lancaster (1988) and Partridge et al. (1990). All three o!er an integrated and multi-disciplinary picture of change in the region over time, and provide analyses which suggest strongly developed di!erences between the southwestern Cape and the rest of southern Africa with respect to the development of Quaternary palaeoenvironments. In reviewing each of these syntheses, emphasis is placed on establishing the broader pattern of environmental change and, in particular, revealing the characteristic environments interpreted for (a) the last glacial maximum (assumed to have been around 18,000 BP) and (b) for the duration of the Holocene (i.e. the last 10,000 yr). This review focuses additionally on any other palaeoenvironmental features regarded of signi"cance and also on any aspects of the palaeoenvironments that compare or contrast with contemporaneous changes elsewhere in southern Africa. 3.1. Deacon et al. (1983) This is not so much a single review as a collection of separate syntheses based on di!erent forms of palaeoecological evidence such as large mammals (Klein,

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1983), small mammals (Avery, 1983) and pollen (Coetzee et al., 1983). The most comprehensive data sets, in as much as they relate to the greatest number of individual sites, emanates from Klein's (1980, 1983) review of the large mammal fossils found at 31 localities distributed across the biome. Using evidence from Nelson Bay Cave, Byneskranskop 1, Bu!elskloof and Boomplaas, which are regarded a falling within the fynbos biome proper, together with the evidence from Eland's Bay Cave and Melkhoutboom Cave just beyond its northwestern and southeastern margins respectively, Klein (1980, 1983) draws the important conclusion that the period of time coincident with the temperate-zone last glacial maximum was characterised by the dominance of grazing, as opposed to browsing, large mammals. Such a situation is consistent with grasslands developed across large expanses of what is currently fynbos and climatic conditions at this time are interpreted to have been both cooler and more moist than presently prevail. Micromammalian evidence does not always accord with this view; at Boomplaas, for example, Avery (1983) suggests that the last glacial maximum period, which is characterised by reduced diversity, was considerably cooler and drier than at present, a conclusion which points to the idea that environmental changes in the fynbos were ¬ necessarily regionally synchronous or comparable throughout the biome' (p. 152) and thus emphasises &the need for caution in "nding an acceptable and meaningful level of generalization or extrapolation from the evidence' (p. 152). The pollen evidence (Coetzee et al., 1983) is uninformative for the last glacial maximum period, which is probably not represented in the polleniferous sites then known. An issue which is not adequately addressed in the Deacon et al. (1983) publication is the palaeoenvironmental indicator value of &grassiness' in the fynbos context; the climatic signal of such an observation is interpreted variously as indicative of &cooler and moister' (Klein, 1983) and &cooler and drier' climatic conditions (Avery, 1983). This conundrum remains unresolved, not least because there are no analogues for such a situation in the biome, except perhaps the grassy fynbos of the eastern parts of the region which prevails under an all-year precipitation regime. Palaeoecological evidence for the Holocene is considerably more abundant. Fossil large mammals indicate conditions broadly like those of today for the last 3000}5000 yr and that the earlier part of the Holocene was somewhat warmer and drier (Klein, 1983). Micromammals at Boomplaas (Avery, 1983) are consistent with this suggestion of an early Holocene drier than today, although sites elsewhere within the biome suggest a much more complex sequence of climatic #uctuations during the Holocene. Pollen evidence available to Coetzee et al. (1983) was restricted to the studies of forest and fynbos development in the coastally-situated Wilderness Lakes of the southern Cape (after Martin, 1968) and the chrono-

logically problematic studies of Schalke (1973) in the southwestern Cape. Very little consistency is apparent between these studies, in part because they deal with di!erent time periods and in part because they are in ecologically distinctive regions. The Deacon et al. (1983) synthesis reveals that there is more discordance than concordance between late Quaternary palaeoenvironmental reconstructions based on di!erent forms of evidence Explanations as to the reasons for such discordance relate to the possibility of interregional variations in climatic response, although the general paucity of evidence coupled with the likelihood that di!erent ecosystem components may respond di!erentially to environmental change cannot be ruled out. 3.2. Deacon and Lancaster (1988) Although written "ve years later, the Deacon and Lancaster (1988) review of Quaternary environmental change in southern Africa as a whole is based on only marginally more evidence than the Deacon et al. (1983) review for the fynbos biome. Deacon and Lancaster (1988) incorporate the pollen work of Scholtz (1986) and are also able to draw on Klein's (1984) analysis of changing large mammal fossil size as well as Deacon et al.'s (1984) multidisciplinary review of the evidence emanating from Boomplaas Cave. From these data, Deacon and Lancaster (1988) note that, although the earlier part of the last glacial maximum may have been both cooler and wetter than present, &2the coldest and driest (our italics) conditions of the last 125,000 yr date (from)2 20,000 to about 16,000 BP (p. 146). Furthermore, Scholtz's (1986) paleoecological data (mainly charcoal) for Boomplaas indicates that a greater proportion of the last glacial precipitation may have fallen during the summer than is currently the case in the southern Cape. The Holocene is uniformly re#ected as a period of temperature amelioration and the mid-Holocene is associated with warmer temperatures than at any time during the previous 125,000 yr (Deacon and Lancaster, 1988), although there is less concensus around the quantity and seasonality of precipitation, which appears to have varied in a more complex manner. Scholtz (1986) describes the Holocene vegetation at Boomplaas and also for the coastal forelands west of George. More xeric conditions seem to have prevailed during the earlier Holocene at Boomplaas, and the peat deposits at Norga, which date only to the last few thousand years, are consistent with the view that the second half of the Holocene was in general characterised by greater available moisture. 3.3. Partridge et al. (1990) Partridge et al. (1990), following a workshop and the conference on southern African environmental change that took place under the auspices of the International

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Fig. 2. Partridge et al.'s (1990) reconstruction of the climatic conditions of the southwestern Cape.

Geosphere-Biosphere Programme at the University of Cape Town in 1989, have published the most comprehensive attempt thus far to synthesise the available Quaternary evidence with a view to establishing regional environmental change scenarios. Their view of environmental changes in ®ion A', the southern and southwestern Cape, indicates a very dry and cool last glacial maximum (see Fig. 2), with temperatures from 5 to 63C cooler than the present day. The synthesis suggests that the Holocene may have been subject to signi"cant #uctuations in available moisture; the immediate post-glacial period appears markedly wetter, followed by the remaining "rst half of the Holocene being drier, coincident with the warmest temperatures recorded. The second half of the Holocene seems to have been associated in general with greater moisture availability than the period 5000 to 8000 BP. 3.4. Concordance and discordance evident in the published syntheses The available palaeoenvironmental evidence indicates some problematic areas of disagreement regarding the nature of late Quaternary climates in the southwestern Cape and these are outlined in Table 1 for three key time periods, viz., the last glacial maximum, and the earlier and later halves of the Holecene. Temperature data present a consistent view that the last glacial maximum was between "ve to six degrees cooler than the present day and that these minima characterised the period from 21,000 to 17,000 BP (Partridge, 1993). The so-called Holocene hypsithermal, or altithermal, of the fynbos

biome occurred during the mid-Holocene, probably around 5,000 to 7000 BP and probably provided mean annual temperatures one or two degrees Celsius warmer ethan the present day (Talma and Vogel, 1992; Partridge, 1993). The precipitation situation, however, is subject to greater controversy, perhaps in part because of the di$culty of reconstructing such a composite climate parameter on the basis of proxy evidence only. The earlier synthesis of Deacon et al. (1983) pointed mainly to a wetter last glacial maximum, while the later reviews of Deacon and Lancaster (1988) and Partridge et al. (1990) o!er the suggestion that this period was in fact rather more xeric in the region. There are three possible sources of such an inconsistency, viz., (a) the data are too few and the proxy evidence insu$ciently reliable to produce any coherent picture of regional precipitation change; (b) more recent data points to a real decrease in available moisture at the time of the last glacial maximum, viz: the earlier analyses were simply misinterpreted; (c) there is spatial di!erentiation across the region in respect of its response to late Quaternary precipitation changes, ie some areas were indeed drier, whereas others were wetter at this time; (d) it is clear that the geographical distribution of studies of the late Quaternary in the southwestern Cape is uneven (Fig. 1). With respect to palynological analyses in particular, the reconstructions have largely been restricted to wetland sites in the mountains (e.g., Norga peats, Scholtz, 1986) or at the coast (e.g., Wilderness Lakes, Martin, 1968). In each of these

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Table 1 Quaternary palaeoenvironmental interpretations based on published regional syntheses for the southwestern Cape region

Last Glacial Maximum 10,000 to 5000 BP 5000 to 0 BP

Deacon et al. (1983)

Deacon and Lancaster (1988)

Partridge et al. (1990)

This paper

Temp

Pptn

Temp

Pptn

Temp

Pptn

Temp

Pptn

! ? &

? ? &

! # &

#/! ! #

! !/# !/#

# #/! #

! # !/&

# ! #

Key: For parameter in question: !, lower relative to present day; #, higher relative to present day; }, approximately equal to present day; ?, uncertain or no data; !/#lower, followed by higher (and vice versa).

cases, however, the fossil sites fall within a part of the fynbos biome that receives an all-year precipitation regime, and it becomes obvious that much of what has been reviewed thus far, including much of the large and micro-mammal evidence from within caves, does not fall geographically within the fynbos sensu stricto (Moll and Jarman, 1984). This opens up the possibility that the spatial di!erentiation in climatic response might have remained hidden due to the &selection' of sites used in synthesis. In attempting to choose between which of these sources of discordance is most appropriate, we now turn to new and more recently published and previously unpublished palynological evidence as to the nature of late Quaternary environments in the region. Given that the region has two major landscape elements, viz., uplands and lowlands, the new evidence is presented in its regional geomorphological context, i.e. its association either with the upland or lowland landscapes of the southwestern Cape.

4. New light on the late Quaternary in the southwestern Cape coastal platform Sites suited to the preservation of fossil pollen grains and their accumulation over extended time periods are relatively uncommon in the strongly seasonal climates of the classically &mediterranean'-climate region of the fynbos biome. Sites especially at the xeric end of the fynbos spectrum have proved elusive. Other, non-palynological forms of palaeoenvironmental evidence have been more forthcoming in these environments and the wealth of archaeological information collated for the coastal region of the Western Cape (see Parkington et al., 1988) bears testimony to the fact that such arid environments, while not always suited to the preservation of polleniferous deposits, frequently favour the survival over time of signi"cant quantities of other fossil materials, in particular those with &harder' structures (i.e. physically and chemically resistant) such as those made of bone, shell and chitin.

4.1. Eland+s Bay Cave Intensive study of the late Quaternary development of human occupation in cave sites such as those at Eland's Bay Cave (Fig. 1) has been responsible for detailed reconstructions of human resource use for substantial periods of the late Quaternary, more speci"cally the Holocene (see Parkington, 1986; Parkington et al., 1988), although information pertaining to the last glacial maximum has been incomplete and therefore di$cult to interpret. The sediments at Eland's Bay Cave have yielded pollen from several levels which casts new light on the nature of the late Pleistocene environments in the vicinity. Eland's Bay Cave is situated just to the south of Eland's Bay township (Fig. 1) and is developed in the Table Mountain Group sandstone coastal cli!s. Sediments preserve evidence of human occupation and resource use in this area of the West Coast which is currently subject to a semi-arid climate (mean annual precipitation is little more than 200 mm) with a markedly seasonal winter rainfall regime. The summary pollen diagram (Fig. 3 and Baxter, 1997) can be viewed in combination with the pollen data presented in Table 2 and shows the presence of particular pollen taxa based on the analysis of 12 sedimentary levels dating from DMS 122, which is accorded a radiocarbon age of older than 40,000 yr BP, through to DMS 138 with an age of 10,660$100 BP, and thus spanning the late Pleistocene and incorporating the last glacial maximum. Pollen concentrations are not, in general, very high, a situation which is typical of cave deposits in a semi-arid situation which is not highly conducive to pollen preservation. The range of pollen types observed is representative of the various sandveld communities which today characterise the Eland's Bay area, although there are variations in occurrence which suggest signi"cant environmental changes during the sedimentary period. Pollen zone EBC-B is particularly noteworthy, as it is approximately contemporaneous with the last glacial maximum. Here, the pollen frequencies of woodland taxa achieve maximum values (Baxter, 1997). Woodland is currently not at all abundant in the Eland's Bay area and is found only in small patches associated only with moister and sheltered

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199

Fig. 3. Summary pollen diagram for Eland's Bay Cave, showing presence of various taxa grouped into communities together with radiocarbon ages and excavation units (after Baxter, 1997).

habitats in the sandstone hills (Sinclair et al., 1986). Pollen of taxa such as Anacardiaceae, Celastraceae, Celtis, Ebenaceae, Ficus, Flacourtaceae, Myrica, Olea, Podocarpus, Santalaceae and Sapindaceae } all indicative of woodland or forest communities, characterise zone EBC-B and point strongly to a signi"cantly moister and cooler situation at the time. Concentrations of total pollen also reach a maximum at this time (Fig. 3), a phenomenon which is also consistent with the prevalence of lower temperatures and greater moisture availability in the cave environment. This part of the fynbos lowlands, it seems, was subject to wetter and cooler climatic conditions at the time of the last glacial maximum. 4.2. Verlorenvlei The palynological reconstructions of Meadows et al. (1994), Baxter and Meadows (1994), Baxter and Davies (1994) and Meadows et al. (1996) for Verlorenvlei, also on the western Cape coast, provide an excellent opportunity to view the Holocene environmental developments in the fynbos-karoo ecotone. Organic sediments have accumulated in the Verlorenvlei, an estuarine/coastal lacustrine habitat which record changes in hydrological inputs, climates, sea levels and human activities over a 5000 yr

period. Rising sea levels #ooded the site at Grootdrift, some 15 km from the present day mouth of the Verlorenvlei, shortly after the onset of organic sedimentation around 5100 yr BP. Palynolgical evidence (Fig. 4), in the form of more elevated Asteraceae and Chenopodiaceae pollen concentrations may suggest that the wider catchment at that time was perhaps more arid than today (Meadows et al., 1996). Subsequent vegetation developments, after 3800 BP, indicate the maintenance of a higher sea level followed by regression and loss of sediments from the Grootdrift site. Replacement of the marine in#uences by those associated with a freshwater hydrology is documented in the pollen evidence and points to the immediate pre-Colonial period as one associated with signi"cantly greater moisture availability in the catchment. Human activities markedly disturb the vegetation patterns in the past two hundred years (Baxter and Meadows, 1994). The pollen spectra are broadly consistent with the suggestion of a midHolocene which is drier and probably warmer than present followed by a later Holocene which, at least until the onset of more signi"cant human impacts following the colonisation of the area by European farmers, would have been associated with higher levels of available moisture.

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Table 2 Elands Bay Cave total pollen counts DMS sample number

DMS 138

Anacardiaceae Aponogetan (cf ) Asteraceeae Stoebe type Asteraceae (echinate) Broken/obscured Celastraceae Celtis Drosera Ebenaceae Ericaceae Ficus Hyacinthaceae Iridaceae Kiggelaria Lamiaceae Mesembryanthemaceae Myrica Olea Oxalis Phragmites (cf ) Poaceae undi!. Podocarpus Proteaceae Restionaceae Rosaceae Salix Santalaceae Sapindaceae Solanaceae Unidenti"ed Zygophyllum Charcoal presence Pollen Sum Pollen grains, g\ Pollen grains, cm\

142

144

147

149

150

D, S 87

88

7 0 2 11 37 25 0 0 16 0 0 0 0 0 0 10 0 0 0 0 61 0 0 19 0 0 5 12 3 23 3 **

27 0 4 4 31 18 0 0 13 0 0 0 0 0 0 6 0 0 0 0 29 0 0 2 0 0 0 3 6 14 5 *

32 0 18 11 9 8 0 0 14 0 0 0 2 0 6 0 0 8 0 0 102 0 1 15 11 0 0 4 0 17 3

0 0 0 0 17 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 11 0 0 0 0 0 0 7 0 3 0 *

0 0 0 0 43 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0 0 *

7 0 0 0 27 11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 30 0 0 9 0 0 0 3 0 9 0

0 0 16 6 45 13 0 0 1 3 0 0 1 0 0 0 0 15 0 0 93 9 0 0 0 0 0 0 0 13 0

3 3 62 49 22 9 6 13 13 3 0 8 29 0 24 1 0 25 0 0 245 0 0 2 0

234

162

261

43

62

96

1560 811

810 454

1740 818

172 95

248 129

384 207

119

120

121

122

10 8 19 49 0

19 0 0 11 13 38 0 0 0 0 6 0 0 23 7 0 5 14 0 127 31 2 0 0 0 2 0 4 0 37 0

0 0 0 97 41 0 0 0 0 0 0 0 0 0 0 0 0 0 0 136 17 0 0 0 0 0 0 0 0 19 0

0 0 0 5 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 6 0

0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 2 0

214

600

352

310

31

8

1427 699

6316 3411

2347 1572

2067 1219

124 58

32 18

5. New light on the late Quaternary of the Cape Fold mountains

region as a whole and in comparison with other forms of evidence.

The Cape Floristic Region's proli"c plant species diversity is concentrated in the mountains of the southwestern Cape and it has therefore been a key goal in biogeography to attempt to reveal the role of Quaternary environmental change in the evolution of that diversity (Linder et al., 1992). The uplands of the region are well endowed with wetland sites which have accumulated organic sediments potentially suitable for pollen analysis, but the deposits are frequently shallow in depth and do not extend very far back into the Holocene (Meadows, 1988; Linder et al., 1992). Nevertheless, it is now possible for the palaeoenvironmental implications of palynological analyses of sites from within the Cape mountains to be seen in the context of the

5.1. The Cederberg Pollen preserved in vlei sediments from the Cederberg mountains, at the northern end of the fynbos biome (Fig. 1) has revealed a vegetation history spanning the last 14,500 yr (Meadows and Sugden, 1990, 1991). The record, for the central and highest parts of these mountains, is one of overall stability, despite the fact that the sediments straddle the late Pleistocene-Holocene boundary which has proved a period of marked environmental dynamism in other parts of southern Africa (see Partridge et al., 1990). The last glacial maximum period is not visible from these vlei sediments, although Sugden and Meadows (1991) use the long-term decline in the

Fig. 4. Comprehensive pollen diagram for Grootdrift, Verlorenvlei (after Baxter, 1997).

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abundance of the endemic Clanwilliam cedar, =iddringtonia cedarbergensis, to infer that last glacial conditions may have been more favourable to this tree species and, accordingly, were cooler and wetter than present. That the last glacial in these mountains was cooler and wetter was a hypothesis remained untested until the work of Scott (1994) on hyrax midden deposits from the northeastern side of the Cederberg. Scott (e.g. Scott and Bousman, 1990; Scott and Cooremans, 1992; Scott and Vogel, 1992) has pioneered the use of hyrax (small, rabbit-sized herbivores belonging to the genus Procavia) dung heaps as e!ective pollen traps and therefore useful palaeoenvironmental indicators. The most obvious advantage of such deposits is that, unlike the more conventional polleniferous sediments, they are frequently associated with semi-arid and even arid environments. Scott's (1994) pollen analysis of hyracium at the Pakhuis Pass Shelter (Fig. 1) yields a picture of changing environmental conditions during the late Quaternary at the xeric end of the mountain fynbos spectrum, since the area annually receives only around 450 mm precipitation (winter maximum) per annum in contrast to the vlei sites examined by Meadows and Sugden (1990, 1991) which currently receive probably twice that amount. Scott's (1994) pollen zone A, which is dated as older than 14000 BP and encompasses the late Pleistocene and includes the last glacial maximum, is dominated by pollen of Scrophulariaceae-type, Stoebe-type, Cli+ortia, ¸obostemon and Proteaceae and several ericoid elements. This is interpreted by Scott (1994) as indicative of a lowering of vegetation belts at this time and the shift, therefore, of vegetation types associated with higher altitude in the Cederberg to the lower slopes. Although not explicitly stated as such by Scott (1994), this implies cooler and possibly moister conditions at this time, since the contemporary climatic gradient is one of decrease in temperature and increase in precipitation with altitude in these mountains. Higher frequencies of Ericaceae pollen in zone would support this suggestion, since the heath elements of the Cederberg are more abundant at higher altitudes where temperatures are cooler and precipitation inputs higher (Sugden, 1989), although Scott (1994) steers clear of assigning any moisture signals to most of the vegetation changes evident. Cyperaceae and Restionaceae pollen do reach a peak dated between 16,000 and 15,000 BP and may indicate greater abundance of local wetland elements at that time. The Holocene sequences are in contrast to the earlier pollen levels at Pakhuis (Scott, 1994), suggesting that tree taxa became signi"cantly more abundant in response to the climatic amelioration which followed the last glacial maximum. Pollen of taxa such as Aizoaceae (mainly succulents and frost-sensitive) and asteraceous shrubs peak between 8000 BP and 6000 BP and point to the warmest periods of the Holocene as being times with lower moisture availability. In general, as elsewhere in

the southwestern Cape, the "rst half of the Holocene is associated with more xeric conditions than the last 5000 yr. Woody elements in these hyracium deposits are generally more abundant in the Holocene and, in contrast to the long-term decline in =iddringtonia which points to the impact of pre-Colonial occupation on the Cederberg landscape (Sugden and Meadows, 1991) show reductions in frequencies only in the most recent levels. The Cederberg's rich supply of late Quaternary palaeoenvironmental information is suggestive, broadly speaking, of subtle but important environmental changes. The more upland sites may have been less sensitive to climatic #uctuations, but the lower altitude situation as revealed by Scott (1994) points to a last glacial maximum which was certainly cooler by several degrees, and quite possibly (if the environmental gradients of the present day trended in a similar direction in the past) associated with higher rainfall. Furthermore, periods of higher temperatures during the Holocene were marked by more xeric climates in these mountains. 5.2. Cecilia Cave, Table Mountain Cecilia Cave (Fig. 1) is situated on the eastern #anks of Table Mountain near Cape Town, at an altitude of approximately 550 m. The mouth of the cave faces southeast and is therefore ideally situated as a pollen trap for material borne on the strongly prevalent summer wind direction. Sediments from the rear of the cave (Fig. 5) have revealed a complex sequence of organic and other deposits and pollen has been derived from several levels within this sequence to facilitate the construction of a pollen diagram (Baxter, 1989; Fig. 6). Radiocarbon dates of 7880$80 BP (Pta-5018) at 60 cm and 1970$50 BP (Pta-5024) suggest that the surface 60 cm of deposit has accumulated intermittently within the Holocene (Baxter, 1989) and ages have been interpolated for all the pollen levels sampled. At least 30 di!erent non-arboreal pollen taxa have been identi"ed (Baxter, 1989), although only those constituting more than 1% of the pollen sum are shown in Fig. 6. Arboreal pollen represents a very small proportion of total pollen counted, although changes in frequencies are plotted on the pollen diagram. The diagram reveals rather few changes of note and is, perhaps, more signi"cant for the indications that it provides of relative stability of the surrounding vegetation. On the basis of such evidence, the natural vegetation of this part of Table Mountain, which currently consists of a mosaic of mountain fynbos and Afromontane forest has not been subject to environmental changes of high amplitude during much of the Holocene. That the sample nearest the sediment surface is probably not contemporary is indicated by the low percentages of Pinus pollen; it would be reasonable to expect considerably elevated pine pollen percentages if the sediments post-dated the introduction of this exotic

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Fig. 5. Sediments at Cecilia Cave (after Baxter, 1989). Crosses indicate the positions of samples used in pollen analysis.

tree to the area, as the site lies above a substantial pine plantation. Low percentages of pollen of the Afromontane taxa may be a function of low pollen productivity in many of these trees coupled with the aspect of the cave, which, in facing southeast, is most likely to entrap pollen produced by anemophilous and/or summer-#owering species. Notwithstanding the absence of marked pollen frequency changes, Baxter (1989) does point to some

features of palaeoenvironmental signi"cance. The lowermost pollen spectrum, dated to around 8000 BP, has the lowest values for pollen concentration coupled with highest frequencies of asteraceous pollen } a situation which prompts Baxter (1989) to draw the conclusion that environmental conditions at the time were perhaps drier than currently prevail. The possibility that the spectra at this point are biased by poor preservation exists, but the situation is not inconsistent with the idea

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of drier and, perhaps, warmer conditions in the earlier Holocene. The more xeric phase is followed by a level in which the higher frequencies of both Ericaceae and Restionaceae are consistent with a scenario of greater moisture availability and again, tentatively, slightly cooler temperatures. Baxter (1989) interpolated this to have occurred approximately at around 3500 BP, although, since the chronology is not well "xed, it would be better to describe this simply as a mid-Holocene situation. The coincidence of (marginally) lower temperatures and greater moisture availability is worthy of note, especially in the context of the similar conclusions reached elsewhere in the fynbos biome in respect of the midHolocene.

6. A revised synthesis Given the recently published and previously unpublished palaeoecological evidence that is presented here, it is now deemed possible to present a fresh synthesis of the indicated late Quaternary palaeoenvironmental changes in the southwestern Cape. Although the palaeoenvironmental evidence for the southwestern Cape region remains poorly distributed in both time and space, in the light of the additional information presented here, it is possible to reconsider, albeit tentatively, the three fundamental questions outlined in the introduction. (a) The most important characteristics of the late Quaternary climates are emerging with a consistent pattern. At least within the true winter-rainfall area of the southwestern Cape region, the evidence points to a last glacial maximum which appears to have been markedly cooler than the present day, (a conclusion which has never been in dispute), while at the same time characterised by greater available moisture (e.g. Eland's Bay Cave and Cederberg). The Holocene is e!ectively divisible into two, having a "rst half associated with warmer (hypsithermal) and drier conditions and a second half with temperatures around those of the present day under conditions in which moisture is largely more freely available than it is today. (b) This reconstruction is shown in Table 1. There is some evidence to suggest that the region has not responded uniformly to the changes of the late Quaternary. Logically, such a conclusion is to be expected, since the southwestern Cape is today characterised by marked regional di!erences in, for example, the seasonality and quantity of rainfall, but there are now emerging indications that the southern Cape, centred on George (and today experiencing a more all-year precipitation regime), 䉳 Fig. 6. Pollen diagram for Cecilia Cave, Table Mountain (after Baxter, 1989). Percentages are relative and the pollen sum is 400 identi"able grains in the case of each level sampled. Sample numbers refer to positions in section shown in Fig. 5.

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has experienced a late Quaternary climatic history rather di!erent from that of the winter-rainfall region proper. This is best illustrated in respect of the last glacial maximum, which does seem to have been cooler and drier in the southern Cape (e.g. Boomplaas) and cooler and moister in the western Cape (e.g. Eland's Bay). In this sense, the southern Cape has responded to late Quaternary precipitation changes in phase with the summer}rainfall interior (see Partridge et al., 1990), while the winter}rainfall southwestern Cape has been out of phase. The coincidence of warmer temperatures with drier conditions over the late Quaternary (and vice versa) of the winter}rainfall region appears, then, to contrast in respect of moisture by comparison with much of the rest of southern Africa (see Partridge et al., 1990). This observation has some interesting implications for the prediction of the response of climate to the widely anticipated global warming. Admittedly the forcing mechanism involved in contemporary climate change is unique, but if the patterns of change observed for the late Quaternary are maintained, then any increase in mean annual temperatures in the winter}rainfall region of the southwestern Cape should be accompanied by a reduction in precipitation and lower moisture availability. The lessons of the late Quaternary should indeed be taken seriously by those involved in land management and planning in the region, for it points to increasingly acute water problems in terms of the burgeoning demands of industry, agriculture and urbanisation.

Acknowledgements The authors would like to acknowledge the "nancial support of the FRD and the University of Cape Town in facilitating this research. Susan Sayers is thanked for cartography.

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