Vegetational History of the Ipswichian/Eemian Interglacial in Britain and Continental Europe

Vegetational History of the Ipswichian/Eemian Interglacial in Britain and Continental EuropeAuthor(s): Linda PhillipsSource: New Phytologist, Vol. 73, No. 3 (May, 1974), pp. 589-604Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2431127 .

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New Phytol. (I974) 73, 589-604.

VEGETATIONAL HISTORY OF THE IPSWICHIAN/ EEMIAN INTERGLACIAL IN BRITAIN AND

CONTINENTAL EUROPE BY LINDA PHILLIPS*

The Botany School, Cambridge

(Received 29 October I973)

SUMMARY

The vegetational history of the Tpswichian (last) Interglacial in Britain is discussed in terms of the behaviour of the various trees and shrubs, the marked opening of the vegetation in the latter part of the interglacial, and climatic indications given by the plant assemblages. The vegetational history of the correlative Eemian Interglacial of the European mainland is surveyed geogra- phically, with particular reference to the differences between the Continent and Britain, and to the variations in the flora and vegetational history between north-west Europe, Poland and southern Europe north of the Alps. Special attention is given to the behaviour of Tilia, Taxus, Acer, Picea and Abies.

THE IPSWICHIAN INTERGLACIAL IN BRITAIN

The Ipswichian Interglacial is the last of a series of interglacials in the Pleistocene, and has been assigned an age, on the basis of geochemical measurements, of approximately I25,000 years to go,ooo years B.P. At least fifteen Ipswichian Interglacial sites in Britain have been studied palaeobotanically. The sites are located principally in southern and eastern England, though two are further north. Unfortunately, there is no pollen diagram covering the whole interglacial as there is for the preceding Hoxnian Interglacial, but enough sites have now been described for it to be possible to draw some general conclusions on the vegetational history of this last interglacial in Britain. The system of zonation used here is that of West (I968) and the characteristics of the pollen zones and the correlations with the zones of Jessen and Milthers (I928) are given in Table i. The location of the sites and the pollen zones represented at each site are shown in Fig. i.

Notes on tree and shrub taxa Ulmus. On the north-west European mainland, Ulmus pollen frequencies expand

early in the interglacial and there is a pine-elm zone before the development of the mixed oak forest. In England, Ulmus tends to be less important and there are regional differences in its behaviour. At the Ipswichian sites in southern England, the rise of elm takes place much later than the rise of oak. At Selsey (West and Sparks, I960), Ulmus appears at the zone Ip I/II boundary and reaches a maximum early in subzone Ip IIb, while at Ilford (West, Lambert and Sparks, I964) Ulmus appears at the end of subzone Ip Ib but does not form a continuous curve until subzone Ip Ilb and then remains at low levels. At East Anglian sites where the early zones are represented, Ulmus rises rapidly to a maximum before the main rise of Quercus. Ulmus has maxima in subzones Ip Ib and Ip IIa at Ipswich (West, I957), in subzone Ip Ib at Swanton Morley and early in subzone Ip IIa at

* Present address: Department of Geology, Imperial College, Prince Consort Road, London S.W.7.

589



590 LINDA PHILLIPS

Mundesley (Phillips, I973). The early expansion of the elm at these eastern sites supports the suggestion that the tree had eastern rather than southern refuges (West and Sparks, I960). The elm maximum is also higher at the eastern sites than at the southern ones, the highest being 80% of arboreal pollen (AP) at Ipswich. This is probably a result of growth

miles e eS b tKS a 0 50

A~ '9 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ZONE 14

e De l4

.IV I

Ip II I I

b 13

two]~~~~~~~ I@81 pbk.. b 3

'p1 5 34

L Wo

2

Fig. i. Ipswichian Interglacial sites in England, and zones represented (based on Sparks and West, 1970).

Table i. Characteristics of Ipswichian pollen zones (based on West, I968)

Early-glacial e De High NAP Jessen and Milthers (I928)

Post-temperate Ip IV Pinus i Late-temperate Ip III Carpinus g Early-temperate Ip Ilb M.o.f., Pinus, Acer, Corylus f

Ip IIa Pinus-Quercus e Pre-temperate Ip Ib Pinus-Betula d

Ip Ia Betula-Pinus c Late-glacial 1 Wo High NAP a,b

Abbreviations: e De, early Devensian; Ip, Ipswichian; 1 Wo, late Wolstonian; M.o.f., mixed oak forest; NAP, non-arboreal pollen.

on rich soils not yet podsolized under the influence of pine, combined with freedom from the competition of oak.

Alnus. The behaviour of Alnus in Ipswichian Interglacial pollen diagrams is erratic. Alnus pollen is usually virtually absent, but at Wretton (Sparks and West, I970) and Beetley (Phillips, I973) it is high in zone Ip II, at Mundesley and Swanton Morley it is high at the very end of zone Ip II and in zone Ip III, at Hutton Henry (Beaumont,



Ipswichian/Eemian Interglacial 59I

Turner and Ward, I969) it is quite high in zones Ip II and III and at Austerfield (Gaunt et al., I972) it is high in zone Ip III. One possible explanation put forward for the scarcity of Alnus in zone Ip III at Wretton was a climatic change to drier conditions, although a purely local explanation, involving the effects of changing water-level regime on the development of alder fen carr in the river valley, was favoured. At Hutton Henry Alnus was considered to be an important constituent of the forest, but at Austerfield the high Alnus pollen levels were again thought to represent a local concentration of alder near the site of deposition.

The inconsistent behaviour of the Alnus curve in Ipswichian pollen diagrams, and the association of high Alnus pollen frequencies with the presence of macroscopic remains at Wretton and Swanton Morley, support the idea of Alnus forming very local alder carr communities rather than being an important constituent of the regional woodland. In this respect, the Ipswichian in Britain differs from the Eemian on the Continent, where Alnus appears just before Corylus and remains at fairly high levels through most of the interglacial, and particularly in the mixed oak forest zone.

Acer. It is interesting that all the Ipswichian macrofossil finds of Acer belong to one species, A. monspessulanum. This is a species of scrub and open woodland on dry calcareous soils in the Mediterranean and Middle East. It is not native in Britain today and the summers are not warm enough for it to produce viable fruit.

At Ipswich (West, I957), Stone (West and Sparks, I960) and Trafalgar Square (Franks, I960), Acer pollen has high percentages at the levels where macroscopic remains occur. It has been concluded that Acer behaves in a similar way to Alnus in the Ips- wichian, being locally abundant at some sites but having no significance in the regional forest vegetation (West, I964). At Swanton Morley, Acer pollen is low in the spectrum from sample SX in which the fruit of A. monspessulanum was found. This may indicate that the tree was not abundant even locally, but grew sparsely in small areas of open scrub, perhaps on chalky patches on the surrounding chalky boulder clay slopes.

It is unlikely that an open scrub species such as A. monspessulanum would be growing in closed mixed oak forest, and the widespread occurrence of this species is probably due to the position of the deposits in river valleys. Species such as A. campestre or A. platanoides are more likely to have occurred in the regional forest, and both these species are commonly found in Continental Eemian deposits. The pollen of A. monspessulanum can be distinguished from that of other species by its thick ektexine and by striae that are more equatorial than meridional. At Swanton Morley only one grain of Acer could be tenta- tively referred to this species, so it is probable that at least one other species was present, as a minor constituent of the regional forest.

Macroscopic remains of A. monspessulanum, though common in Britain in the Ips- wichian, have not been found in Eemian-deposits on the Continent, although there is no reason to suppose that conditions on the Continent were less suitable for the growth and reproduction of this species. A. monspessulanum is now distributed all round the Mediter- ranean basin and in the Ipswichian it may have migrated into Britain via the west coast of Portugal, Spain and France, while being excluded from north-west and central Europe by the Alps and other mountain chains. The same may be true of the Mediterranean shrub Pyracantha coccinea, which has been recorded from Selsey and Wretton.

Picea. There is macroscopic evidence for the presence of Picea in the Cromerian and Hoxnian Interglacials and in the Chelford Interstadial. However, the presence of spruce in Britain in the Ipswichian Interglacial, and therefore the existence of a spruce zone (zone h of Jessen and Milthers, I928), has been questioned. At Histon Road, in zone Ip



592 LINDA PHILLIPS

IV, it was suggested that Picea was absent, or that it was present in small quantities and could not spread on account of difficult edaphic or climatic conditions (Sparks and West, I 959). Again, the small rise in Picea at the end of zone Ip II at Aveley was attributed either to transport of pollen from the Continent, or to the limited occurrence of the tree in south-east England (West, I969). In the discussion of Jpswichian vegetational history at Wretton, it was concluded that Picea was absent from Britain in the Jpswichian, probably due to the early establishment of a sea barrier to migration (Sparks and West, I970).

Picea is a relatively low pollen producer, and the tree may be actually growing at a site and yet contribute very little to the pollen rain. At Chelford (Simpson and West, I958), Picea pollen constitutes 3 % of the AP in a mud layer containing a stump and abundant cones and needles of Picea, while at Beetley Picea reaches 6% AP in the levels at which needles are abundant. In Poland, macroscopic remains of Picea were found in Eemian zone g deposits at Rumlowka (Srodon, I950) and at Koszary (Srodon, I957), at levels where Picea pollen reached a maximum of only 0.2% AP. Srodon (I967) assumed that in forest zones an average Picea percentage of o.6-i.o may indicate its presence, while I . I-3.0 is a certain indication in most cases. On this basis, Picea easily reaches sufficiently high levels at the end of zone Ip II at Beetley, Swanton Morley and Ilford for the tree to have been actually present. Picea has a maximum of 70%, 90% and io0% AP respectively at these sites.

The low percentages for Picea in zones II b (f) and III (g) in England and on the Continent contrast with its high levels in zone h on the Continent. Picea values vary from 23% to 64% AP in zone h in Danish deposits (Jessen and Milthers, I928) and usually from 4000 to 60% AP at Polish sites. As yet, however, no spruce zone has been found in Ipswichian deposits in Britain. At Histon Road (Sparks and West, I959) a Carpinus- dominated zone (Ip III) is followed by a Pinus-dominated zone (Ip IV) and Picea is low throughout. It was stated that vegetation trends are not greatly upset across the zone boundary so that the later zone follows on directly from the earlier one with no dis- continuity. Nevertheless, the Pinus curve shows a sharp rise across the boundary, while the levels of Quercus, Carpinus and Corylus pollen fall dramatically. There is a layer of sandy gravel at the zone boundary and it is possible that an intervening zone with higher Picea levels is missing. If there was a spruce phase in Britain, it seems likely from the trend across Europe that Picea would have been relatively low and the tree may not have become a regional dominant.

The complete lack of zone h deposits in Britain may be because Ipswichian deposits are characteristically fluviatile in origin and conditions were unfavourable for deposition in river valleys at this stage in the interglacial. Unless an Ipswichian lake deposit is dis- covered, giving a vegetational sequence that covers the latter part of the interglacial, deposits of this age are most likely to be found in inland situations, in the upper reaches of river valleys where the effects of erosion at a time of falling base level would be felt least.

Carpinus. The Late-temperate zone of the Ipswichian is characterized by the dominance of Carpinus. Andersen (I964) pointed out that the expansion of Carpinus, a shade tree, caused a decline in Quercus and Corylus in this zone and West (I969; and in Sparks and West, I970) commented on the successional nature of this vegetational change with no need for a change in climate to produce it.

Carpinus immigrated late into Britain in the Ipswichian and then rose rapidly to dominance. The taxon makes its first appearance in subzone Ip IIb at Aveley, Ilford, Wretton and Swanton Morley, and at Selsey and Ipswich it is not present at all in this



Ipswichian/Eemian Interglacial 593 subzone. The earliest recorded occurrence is at Mundesley where single grains were found in two samples from subzone Ip IIa. Carpinus shows this pattern of late immigration in all the interglacials after the Pastonian, and West (I970) suggested that the genus has become poorer in biotypes since the Pastonian and has only been able to survive at a considerable distance in subsequent glaciations. Carpinus is tolerant of a range of climatic conditions, but fruiting is prevented by early spring frosts (Christy, I924) and this may have influenced its area of survival in glacial periods.

Carpinus has been recorded from Ipswichian sites considerably north of its Flandrian distribution in south-east England, as pollen at Hutton Henry and as pollen and nuts at Austerfield. This may be an indication of warmer summers or of the absence of spring frosts in the Ipswichian, although the causes of the present restriction of range of Carpinus in Britain are not clear and may not be solely climatic. Carpinus immigrated late into Britain in the Flandrian and it has traditionally been coppiced, with only isolated trees being allowed to reach maturity. The present limits of the hornbeam may partly represent the area of warm summers and frost-free springs which promote heavy fruiting, and may also reflect the extent to which the tree had expanded before human interference prevented further spread.

Carpinus values in the Ipswichian tend to be higher in Britain than on the Continent and this has been attributed partly to the absence of Picea from British sites, as this tree competes strongly with Carpinus through its podsolizing effect on the soil (Sparks and West, I970). At Beetley Carpinus is low even late in subzone Ip Ilb while Picea is present at higher levels than are usually found in this subzone. In this respect the Beetley assemblage resembles that from Ilford, where Carpinus and Picea are both at significant but fairly low levels at the end of subzone Ip IIb. This relationship between Picea and Carpinus is also seen in the Hoxnian diagram from Nechells, Birmingham (Kelly, I964) where at the beginning of the Late-temperate zone (III) the usually fairly high Carpinus levels are replaced by an expansion of the Picea curve. The depressing effect of Picea on Carpinus in the diagrams from Beetley and Ilford may be regarded as further evidence for the presence of Picea in Britain in the Ipswichian Interglacial.

Tilia. Tilia is virtually absent from most Ipswichian pollen diagrams, and West (I96I) suggested that a comparatively early rise in sea level in the Ipswichian might have been responsible for the exclusion of Tilia from Britain. Relatively high Tilia pollen levels were later recorded in subzone Ip IIb deposits at Ilford and Aveley, where Tilia reaches 500 and 9?0 AP respectively. West (I969) concluded that although long-distance transport of pollen could be involved, Tilia might have been present in south-east England.

Tilia was a late immigrator on the north-west European mainland, not appearing until subzone Ip Ilb in Denmark or the Netherlands (zone f in Denmark, Jessen and Milthers, I928; zone E4b at Amersfoort, Zagwijn, I96I). Its expansion in the mixed oak forest at these sites is very limited. It would not be surprising, then, if Tilia failed to reach Britain even if the creation of the sea barrier were not particularly early. At the same time, the presence of other late-immigrating taxa such as Carpinus and probably Picea suggests that Tilia could have come into Britain and the relative abundance of Tilia pollen at the south-eastern sites supports this possibility.

The Late-temperate NAP rise A marked increase in non-arboreal pollen (NAP) late in subzone Ip lIb and in zone

Ip III is a characteristic feature of Ipswichian pollen diagrams. The phenomenon is



594 LINDA PHILLIPS

probably related to the situation of Jpswichian deposits in river valleys. The increase in herbaceous vegetation is primarily a local feature resulting from the infilling of river channels when the rise in sea level halted in subzone Ip Ilb, followed by aggradation in the valleys with the renewed rise in sea level in zone Ip III. Such an interpretation is supported by the absence of this rise in herb pollen at Continental Eemian sites, where the deposits are in different situations and the pollen diagrams show the more usual pattern of high AP until the closing stages of the interglacial. There are also two English sites, Hutton Henry and Austerfield, where the NAP rise does not take place and pollen of open habitat herbs is rare. In both cases, deposition took place in a terrestrial or lacustrine rather than in a river situation.

At Wretton the rise in NAP at the end of subzone Ip Ilb was thought to be due to infilling of the river channel (Sparks and West, 1970). The rise in NAP at Mundesley is rather earlier, taking place in subzone Ip Ila, but again appears to be related to the final infilling of the channel. The spread of open habitat plants in zone Ip III was attributed to flooding and aggradation of alluvium at Aveley (West, I969) and at Ilford (West et al., I964). At Beetley and Swanton Morley the NAP rise can be related to the aggradation of sand and gravel in the river valleys, although at Beetley the effect is probably exaggerated by the generally poor soils of the area over the Wolstonian outwash gravels.

There is evidence from several sites that a more general opening out of the forest vegetation may be taking place. There are pollen records of chalk grassland species in zone Ip III at Histon Road (Sparks and West, I959) and at Wretton, and macroscopic remains of shrubs of calcareous scrub vegetation at Wretton, and in subzone Ip Ilb at Ipswich (West, 1957). These records were taken to indicate the existence of open areas on the surrounding chalk or chalky boulder clay uplands. In the subzone Ip IIb and zone Ip III samples from Swanton Morley, Acer monspessulanum and Sambucus nigra are present macroscopically, and the herb pollen includes Helianthemum, Plantago major/media and Poterium sanguisorba. The two latter species are also present in subzone Ip IIb at Beetley, and in the same subzone at Mundesley pollen of Helianthemum, Reseda lutea and Scabiosa columbaria has been recorded. Andersen (i964) noted some increase in herbs and shade-intolerant taxa at Herning in Denmark at the same time as the rise to dominance of Carpinus, a shade tree. He ascribed the NAP rise to soil poverty and the development of raw humus through leaching and the increase of Picea. This explanation cannot be applied to the rise in calcicolous species at English sites and some other reason must be found, although the effect is very slight. The presence of Mediterranean scrub species such as Acer monspessulanum and Pyracantha coccinea may point to greater summer dryness which could result in a more open woodland.

Remains of large mammals are commonly found in deposits of this age and extensive mammalian faunas are known from several Ipswichian sites, notably Ilford and Trafalgar Square. Large mammals are associated with the Ipswichian deposits at Aveley, Beetley and Mundesley, and at Swanton Morley all the zone Ip III samples were taken from inside bones of Hippopotamus and Bos primigenius, while a subzone Ip IIb sample came from a tooth of Elephas antiquus. It is likely that these animals would have affected the vegetation, and animal activity is indicated by the relatively high levels of Plantago lanceolata pollen at Aveley, Ilford, Trafalgar Square, Beetley and Swanton Morley, and by the presence of P. major/media pollen at Histon Road, Wretton, Beetley and Swanton Morley, as P. major is encouraged by animal treading.

When animal numbers are high, grazing, browsing and trampling will lead to a reduc- tion in forest cover and to the maintenance of open vegetation where this already exists.



Ipswichian/Eemian Interglacial 595 Animals such as deer and cattle eat tree seedlings and often damage young trees. In Africa today, elephants create open areas through browsing and ring-barking and break- ing down trees, although the population density is often unnaturally high. Hippopotami graze on grasses as well as water plants, and open out long-grass communities. Where they are numerous, bare areas are created near the river and river banks are eroded.

There are some indications that animal activity has no more than local significance at some sites. At Beetley, for instance, the spectrum from the Hippopotamus bone falls early in subzone Ip lIb and AP is still high. Furthermore, at several sites Umbelliferae are important in the high NAP phase, and plants of this family are extremely sensitive to trampling and become greatly diminished where there is animal activity (Voisin, I960).

Animal activity is unlikely to be the prime cause of the rise in NAP in the Ipswichian Interglacial. It is more probable that in subzone Ip Ilb and zone Ip III, the filling of river channels and subsequent aggradation resulted in an increase of open herbaceous vegetation in the river valleys. Animals on the floodplain would have hindered tree and shrub colonization and would have maintained and extended the open habitats in the river valleys, possibly creating some open areas in the woods on the surrounding hillsides as well.

Indications of climate A variety of factors is responsible for differences in the flora and vegetation of dif-

ferent interglacials in any one area (West, I96I, I970). It is hard to assess the relative importance of climate as a factor, particularly as so little is known about the climatic tolerances of modern species. However, some climatic inferences can be drawn where fossil fruits are found of species that rarely or never fruit in the area today, and where there are pollen or macros of plants whose climatic limits have been studied, notably Viscum, Hedera and Ilex (Iversen, I944). There remains the possibility that the climatic requirements of plants have changed through selection of biotypes in successive glaciations, but this problem is reduced if a group of fossil plants points to a consistent con- clusion.

In Britain in the Ipswichian, zone II has an assemblage of thermophilous water plants which indicates that summers were warmer than they have been in the Flandrian. Trapa natans, Naias minor and Salvinia natans require warm summers to set seed and they fruit on the Continent today, but have been absent from Britain in the Flandrian. Lemna minor rarely fruits in Britain, and Stratiotes aloides and Hydrocharis morsus-ranae rarely produce viable fruit. A similar but richer assemblage is known from Continental Eemian deposits. There are records of thermophilous aquatics before zone II in Ipswichian deposits, for example Hydrocharis in subzone Ip Ia at Ilford, and Salvinia in subzone Ip lb at Ipswich, reflecting the rapid rise in temperature at the beginning of the interglacial that is indicated by the early immigration of thermophilous trees.

Several shrubs also indicate considerable summer warmth, notably Pyracantha coccinea, a southern European plant whose seeds have been found at Wretton and Selsey, and Acer monspessulanum, a Mediterranean species that does not produce viable fruit when planted in Britain today, but which grew and reproduced freely in the Ipswichian. The presence of warmth-requiring plants in the Ipswichian has been taken to indicate continentality of climate in Britain at that time. There is, however, no evidence for the cold winters that are characteristic of the continental climate, and the common occurrence of Hedera, Ilex and Cladium indicates that winters were not severe. The overall indications are of a Mediterranean climate, with warm dry summers and mild winters. The



596 LINDA PHILLIPS

success of Carpinus in zone Ip III, the general decline in Hedera, the absence of Cladium, and the appearance of Picea on the Continent and perhaps in Britain, may indicate an increasing degree of continentality in this zone; but Ilex persists, the absence of Cladium may only be a result of unfavourable conditions near the site of deposition, and the ecological tolerance of Picea may have changed.

THE EEMIAN INTERGLACIAL ON THE CONTINENT

North-west Europe In their classic work on deposits of the last interglacial in Denmark and north-west

Germany, Jessen and Milthers (I928) described a vegetation sequence for the area which is summarized below.

Zone i Pinus-Picea-Betula h Picea-Pinus g Carpinus-Picea f Mixed oak forest with Alnus, Corylus, Quercus and Tilia e Pinus-Ulmus d Pinus-Betula. Thermophilous trees appear c Betula-Pinus

Very many Eemian sites have subsequently been investigated in north-west Europe and this sequence has been confirmed in Denmark, north-west Germany and the Nether- lands. The zonation systems for these areas have been easy to correlate with the Jessen and Milthers zonation (Table 2), and the general vegetation sequence produced by Selle (I962) for north-west Germany is essentially the same as that of Jessen and Milthers. The uniformity and distinctiveness of Eemian pollen diagrams, with well-marked phases of forest development, contrasts with the situation in the preceding interglacial. Hol- steinian diagrams exhibit considerable regional variation over Europe, and the similarity of Holsteinian and Cromerian assemblages has frequeritly created difficulties in dating deposits.

The main features which distinguish north-west European Eemian diagrams from those of earlier interglacials are as follows.

(i) The dominance of Quercus and Corylus in the mixed oak forest. (2) The characteristic Carpinus zone. (3) The restriction of Picea largely to the later part of the interglacial. (4) The clear sequence of Carpinus-, Picea- and Pinus-dominated zones following the

mixed oak forest. (5) The lack of any strong development of Abies. (6) The absence of taxa such as Pterocarya, Carya, Tsuga, Buxus, Vitis and Azolla, all

of which occur in the Holsteinian Interglacial in north-west Europe. The principal differences between north-west European Eemian diagrams and British

Ipswichian diagrams are the virtual absence of Picea, Tilia and Taxus from Britain, the complete absence of Abies and the variable behaviour of Alnus. Acer pollen percentages are often much higher in Britain than on the Continent, but species are known macroscopically in Europe that have not been found in English deposits (Fig. 3).

There are also differences in the aquatic flora as represented by macroscopic remains. On the Continent, Eemian deposits contain a rich thermophilous aquatic flora, and the



Ipswichian/Eemian Interglacial 597 British aquatic flora, though including many of the Continental taxa, lacks Aldrovandra vesiculosa, Brasenia purpurea and the cyperaceous plant Dulichium spathaceum. Brasenia and Dulichium are monotypic genera that are no longer native in Europe. Brasenia occurs in North America, Eastern Asia and Australia, while Dulichium is confined to North America. Aldrovandra vesiculosa is not found in north-west Europe today, and has a

Table 2. Correlation of north-west European Eemian zonation systems (based on Zagwijn, 196I).

BRITAIN DENMARK NETHERLANDS N.W. GERMANY

(West 1968) (Jessen and (Zagwijn 1961) (Florsch'utz and (Selle 1941) (Selle 1953) Milthers 1928) Someren 1956)

e De e W 6 X VI

Ip IV E b IX I

lp bh -'VIIII

b b TPu 111 g E: 5; 4 V/II IV

b f a S VI b III

IpIT b I3 a | e a s b~~a b

iva E 2W

I Wo~~~~~~~~~~~~~~~~~~~~~~~~

scattered distribution in south, central and east Europe. All three plants are very common in Eemian deposits all over Europe, and Brasenia flourished enough to produce peat at the beginning of the interglacial in the North-East Polder in Holland (van der Vlerk and Florschiutz, I953). There are, however, no records of Dulichium from Holland.

The most important Eemian sites in north-west Europe, besides those described by Jessen and Milthers, are at Herning and Hollerup in Denmark (Andersen, I964, I965), at Amersfoort (Zagwijn, I96I) and around Asten (van der Vlerk and Florschiitz, I953; Florschiutz and Anker-van Someren, I956) in the Netherlands, and in north-west Ger- many around Hamburg and Harksheide (Hallik, I957), and at Wallensen (Rabien, I953), Honerdingen (Wolstedt, Rein and Selle, I95I), Weeze (Brelie and Rein, I956) and Ned- den-Averbergen (Selle, I957). These sites, and others mentioned in the text, are shown in Fig. 2.

Within this area there are some interesting features of the flora and variations in the vegetational history. In Denmark and the Netherlands Tilia appears in zone f, has a very low peak and disappears by zone g. In Denmark (Jessen and Milthers, I928) Tilia is rarest in the west but becomes more common in the east and south. In north-west



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Ipswichian/Eemian Interglacial 599 Germany Tilia again has a low maximum just before the rise of Carpinus. Values are higher than in Denmark, usually IO-20% AP at the maximum, and at Honerdingen Tilia reaches 4000. T. cordata and T. platyphyllos have been found macroscopically in Denmark and north-west Germany, and at Wallensen there were also fuits of T. tomentosa in zone f deposits. This species does not grow in Germany today and is distributed in south-east Europe, the Balkans and Turkey.

Neither pollen nor macros of Taxus have been found in Dutch Eemian deposits, but in pollen diagrams from Herning and Hollerup in Denmark (Andersen, I964, I965), Taxus

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~~~~~~ O 0

+0 0

Fig. 3. Species of Acer represented by macroscopic remains in Eemian deposits in Europe. *, A. monspessulanum; + A. campestre; O, A. platanoides; G, A. pseudoplatanus; A, A. tataricum.

appears with the rise of Corylus and Alnus in zone f, reaches a maximum of about 5/0 AP late in zone f, then declines through the hornbeam zone. Seeds and needles of Taxus baccata were recorded at several sites by Jessen and Milthers. In north-west Germany Taxus behaves in the same way but reaches higher levels, with a maximum of I 6% AP late in zone f at the same time as the Tilia peak at a site near Neumiinster (Menke and Ross, I967) and a maximum of 20% AP at Grevenhof, also coinciding with the Tilia peak (Behre, I962). Macros of Taxus baccata were found at Schwindebeck (Behre, I962) and Wallensen, in zone f and g deposits. Taxus was, therefore, a significant com- ponent of the mixed oak forest of north-west Germany when it was at its most varied, just before Carpinus rose to dominance.

Acer is very low in north-west European diagrams and it clearly played only a minor



6oo LINDA PHILLIPS

part in the forest vegetation. Two species are represented by macros, A. campestre and A. platanoides (Fig. 3). Both have been found in Denmark (Jessen and Milthers, I928), and in north-west Germany both species were found at Wallensen, and A. platanoides at Schwindebeck. No macros are known from Dutch sites, and only a few pollen grains were recorded at Amersfoort.

There are macros of Picea from many sites, and the species involved is P. abies. In the pollen diagrams, the behaviour of the Picea curve in the latter part of the interglacial is rather variable, but the variations appear to be local and there are no regional trends discernible in north-west Europe. The commonest pattern is for Picea to rise at the same time as Carpinus, with its main increase delayed until after a clear Carpinus maximum. At some sites, though, Picea is high in the Carpinus zone, depressing and often exceeding the Carpinus values. This is probably a competition effect at sites where conditions were especially suitable for Picea. At some other sites, Pinus rises early so that there is no spruce-dominant phase. This is probably also a local effect, in this case caused by particularly poor soil conditions.

There are no records of Abies from Denmark, which was north of the limit of Abies in the last interglacial. In Dutch and north-west German diagrams, Abies appears at the end of the hornbeam zone and has a low peak in the spruce zone, after which it fades out again. The maximum is usually around 5 % AP, although it is higher at some north- west German sites. Macros of Abies alba were found at Wallensen (Rabien, I953) and Schwindebeck (Behre, I962), and of A. cf. pectinata (= alba) at Grevenhof (Selle, I962). The very limited development of Abies in Holland and north-west Germany and its total absence from Denmark and Britain provide a marked contrast with the Holsteinian, when Abies became very important all over north-west Europe in the later part of the interglacial.

Poland The Eemian vegetational history of Poland is very well documented and there are

many important sites. Diagrams covering the whole interglacial have come from Bedlno (~rodon and Golabowa, I956), Kalisz (Tolpa, I952), the Widawka basin (Janczyk- Kopikowa, I97I) and Otapy (Bitner, I956), and there are several sites in the Grodno area (~rodon, I950). The vegetation succession is very similar to that in north-west Europe and the Jessen and Milthers zonation has often been directly applied to Polish diagrams. There are, however, some significant differences in the vegetation succession and in the flora.

Tilia appears at the same time as in north-west European diagrams, but is more important and there is often a Tilia-Carpinus zone between zones f and g. Tilia maxima increase from Io% at Bedlno and 250% in the Widawka basin in south-central Poland, to 40-55% in the north-eastern sites of Zukiewicze near Grodno, and Otapy. As in north- west Europe, macros of T. cordata and T. platyphyllos have been found. Tilia was evi- dently an important forest tree in the lowlands of northern Europe, and particularly to the east (Fig. 4). Taxus, on the other hand, appears to have been very sparse in Poland, with only a few grains in zone f and g deposits at Zukiewicze where macros of T. baccata were also found. This parallels the present distribution of Taxus.

Acer pollen values are somewhat higher than in north-west European diagrams, frequently around 5 0 in the later part of zone f, and as high as 700 at Bedlno. Four species are known macroscopically, two of which are common in north-west European deposits, A. campestre and A. platanoides. The new species are A. pseudoplatanus and A. tataricum.



IpswichianlEemian Interglacial 6oi

These all occur together in the mixed oak forest zone at Bohatyrowicze near Grodno (Fig. 3). A. tataricum does not occur in Poland now and it is characteristically a species of steppe scrub in eastern Europe and Russia and of mountain woodlands in south-east Europe.

Macros of Larix sibirica (= L. europaea ssp. sibirica), the Siberian larch, were found at Zukiewicze in the early part of the interglacial, in a pine-spruce pollen zone with a little Larix pollen. L. europaea ssp. sibirica is native to north-east European Russia and western Siberia today and does not reach as far south or west as Poland. Very low Larix pollen

H I I I I I I 12 510 20 30 10 50 60 .A P

Fig. 4. Maxima of Tilia pollen at Eemian sites in Europe.

frequencies have also been recorded at sites in the Widawka basin in zones f and i and macros of Larix sp. were found at Bedlno.

Picea frequently rises to much higher levels in zone h in Polish than in north-west European diagrams. It is also important early in the interglacial in Poland and there is a pine-spruce zone before the development of the mixed oak forest. Two species are commonly found macroscopically, P. excelsa (= P. abies ssp. abies) and P. obovata (= P. abies ssp. obovata), the latter primarily in the later part of the interglacial. P. obovata, the Siberian spruce, is often very abundant in Polish Eemian deposits, and the range of the species then extended west of its present limits.

At the south-central Polish sites, Abies rises very dramatically after the Carpinus zone, and exceeds Picea. At sites in the-north-east, however, Abies is very low or absent. 8rodon and Go1a bowa (I956) pointed out that the main distribution of Abies in the



602 LINDA PHILLIPS

Eemian was similar to the present, in the uplands of central Poland, although there were low occurrences north and north-east of the present limit, and they suggested that this interglacial extension of the range may have been due to differences in relief at that time. The range of Abies in Europe has contracted in successive interglacials. In the Holsteinian it spread all over Europe as far as Ireland, in the Eemian it was absent from Britain and Denmark and low in north Germany, Holland and north Poland, and it is now absent from all these areas. A more general explanation than changes in relief is required to account for the changing distribution of Abies in Europe as a whole, and its progressive failure to re-enter north-west Europe in the Eemian and Flandrian may be due to its slow migration from glacial refuges (West, I970).

In the Eemian in Poland, Tilia and Acer play a more important role in the mixed oak forest than in north-west Europe, while Taxus is diminished, and Alnus is also reduced. Conifers assume greater importance and there are taxa present which do not occur in north-west Europe. A new 'Asiatic' element is present in the flora, consisting of Larix sibirica, Picea obovata and Acer tataricum, and these have only been found in Eemian deposits. The flora and vegetation give a general impression of greater continentality of climate than further west, in contrast with the Holsteinian Interglacial when more oceanic conditions extended far into Continental Europe.

Southern Europe Moving south from north-west Europe into south Germany, Eemian deposits at

Zeifen, just north of the Alps, have yielded a rich macrofossil assemblage and an interesting pollen sequence covering most of the interglacial (Jung, Beug and Dehm, I972).

The pollen diagram shows the characteristics of Eemian diagrams further north, and the macrofossils include the variety of thermophilous aquatics seen elsewhere, but the flora and vegetation have some distinctive features.

Tilia appears early, soon after oak and elm, but remains very low, as it does at another southern site at Gainovce in Czechoslovakia (Kneblova', I958). Fruits of two species are present at Zeifen, T. platyphyllos and the south-east European species T. tomentosa. Taxus, however, rises to a peak of nearly 8o0? AP late in the mixed oak forest phase, then declines. The abundance of T. baccata in the macros in this zone and all through the succeeding hornbeam zone shows that yew was flourishing even if only locally. Taxus is much less abundant in northern Europe. This probably reflects lower rainfall in the lowlands to the north, and greater continentality of climate to the east. It may also be due to the slow spread of Taxus from southern glacial refuges.

Acer appears early with oak and elm and is then present throughout, but it never exceeds 200 AP. There are macros of three species, A. campestre, A. platanoides, and A. pseudoplatanus, which was also found at Ganovce (Fig. 3). The modern distribution of A. pseudoplatanus has been distorted by extensive planting, but it is principally a tree of the mountain regions of central and southern Europe and the Eemian occurrences match this distribution. In the Swiss Alps it grows in the deciduous forest just below the conifer zone and extends right up into the coniferous forest, reaching its greatest size above I000 m (Christ, I883). Possible changes in relief in north-east Poland since the Eemian (~rodon and Golkbowa, I956) may explain the interglacial record of this species at Grodno in an area that would now provide a lowland habitat.

Pinus is very low but other conifers are more important in this area at the foot of the Alps than they are in the north-west European lowlands. Picea, the species identified macroscopically being P. abies, appears at the same time as Quercus, and varies between



Ipswichian/Eemian Interglacial 603 IO1 and 300/ AP all through the deciduous forest zones. Abies appears before the rise of Carpinus and remains at I0-20% AP all through the Carpinus zone. Abies appears at the same time at Ganovce and reaches its maximum in the Carpinus zone, so the fir arrives and expands earlier at these sites than in north Germany and Poland.

An interesting feature of the Eemian plant assemblage at Zeifen is the presence of some taxa that in north-west Europe would be considered typical of Holsteinian assemblages. Buxus has low pollen frequencies in the hornbeam zone at Zeifen, and it was also recorded as leaf impressions at Gainovce, and as pollen, with Abies and Picea, at Chambery in the French Alps (Lemee, I952). Vitis pollen occurs at Zeifen, again in the hornbeam zone, and seeds of V. vinifera ssp. sylvestris were found. Vitis and Buxus have also been recorded from Eemian deposits near Berlin (Erd, I962). The combination of Abies, Buxus and Vitis is characteristic of the Late-temperate forests of the Holsteinian Interglacial and their occurrence at these Eemian sites reflects the re-entry of these plants into southern and central Europe from the refuges they occupied in the intervening glacial stage.

ACKNOWLEDGMENTS

This work was carried out during the tenure of a studentship from the N.E.R.C. I should like to thank Dr R. G. West for his advice on this paper.

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Vegetational History of the Ipswichian/Eemian Interglacial in Britain and Continental Europe

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