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Environmental changes during the Late Glacial and Post-Glacial in the central Pyrenees (France): new charcoal analysis and archaeological data
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Review of Palaeobotany and Palynology 104 (1998) 1–17
Environmental changes during the Late Glacial and Post-Glacial in the central Pyrenees (France): new charcoal analysis and archaeological data C. Heinz a,Ł , M. Barbaza b a
UPRESA 5059 of the CNRS, Laboratoire de Pale´oenvironnnements, Anthracologie, Action de l’Homme, Universite´ des Sciences et Techniques du Languedoc, Institut de Botanique, 163, rue Auguste Broussonet, 34090 Montpellier, France b UMR 5608 CNRS, Universite ´ , Culture, U.T.A.H. Laboratoire de Pre´histoire, Maison de la recherche, Universite´ de Toulouse-le-Mirail, 5 alle´es Antonio Machado, 31058 Toulouse cedex, France Received 16 January 1998; accepted 12 June 1998
Abstract The archaeological site at Troubat (Troubat, de´partment of Hautes Pyre´ne´es) has provided the first long charcoal sequence in the central Pyrenees. It offers information concerning the transformations in the vegetation cover due primarily to climate, from the Late Glacial Bo¨lling–Allero¨d interstadial to the middle of the Post-Glacial. Four main phases illustrate the changes in vegetation recorded in the charcoal data. Between about 13,000 B.P. and 11; 320 š 410 B.P. (phase T1) a vegetation with Juniperus, some Rosaceae (Prunus types 1, 2, 3), Rhamnus alpina, R. cathartica=saxatilis, R. pumila, Hippophae rhamnoides and Betula verrucosa is evidence of an open environment with colonising shrub cover established in a climate of dry mountain or even subalpine type. This change is correlated with the Late Glacial interstadial. At about 10; 770 š 100 B.P., a reduction of the Juniperus pioneer stage cover, which developed thanks to the Bo¨lling=Allero¨d warming, together with an increase of Rhamnus and Rosaceae, which would be a response of the vegetation to the first cooling of the Younger Dryas (phase T2). Around 9700 š 80 B.P., a phase of forest colonisation by Corylus and the establishment of deciduous oak forests which corresponds to the Post-Glacial climatic amelioration is noted (phase T3). Then, at about 8625 š 80 B.P., there is affirmation of an increase in deciduous oak forests of ‘collinean’ type. Pinus sylvestris, whose role is minor at Troubat, as well as Corylus, see their frequency diminish in response to an increasingly dense forest environment (phase T4). 1998 Elsevier Science B.V. All rights reserved. Keywords: charcoal analysis; archaeology; Late Glacial; Post-Glacial; central Pyrenees; Troubat; palaeoecology
1. Introduction The archaeological work carried out at the caveshelter of Moulin (Troubat, Haute-Pyre´ne´es) has provided an interesting and prodigious stratigraphy Ł Corresponding
author. Tel.: C33 4 9923-2180; Fax: C33 4 6754-3537; E-mail: [email protected]
concerning the period of the Late Glacial and the beginning of the Post-Glacial (Barbaza, 1988; Barbaza and Heinz, 1992). The long archaeological sequence, almost 4 metres, provides evidence of occupation with very little interruption from the middle Magdalenian (Magdalenian III of Breuil, between 16,000 B.P. and 15,000 B.P.) to the middle Sauveterrian Montclusian (between 9000 B.P. and 8000 B.P.). The
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abundance of charcoal as well systematic sampling have provided the first charcoal sequence for the central Pyrenees; almost 6000 fragments of carbonised wood have been studied. The species list consists of 37 trees, shrubs or bushes representing all the major forest species. Thus using this charcoal data we can trace the evolution of the plant cover and the changes in the vegetation over about 5000 years, from about 13,000 B.P. to 8000 B.P.
2. The site The cave shelter of Moulin at Troubat (HautesPyrenees) was formed in the Mesozoic limestone
which makes up the northern border of the Pyrenees (Fig. 1). It is situated at an altitude of 541 m near the Ourse basin in the region of the Garonnais piedmont. The valley of the Barousse consists of oceanic middle mountain landscapes. In the context of bioclimatic zones, it is a transition zone; the site itself located on the flank of the Gouade`re massif which rises to 800 m at the conjunction of the supra-Mediterranean vegetation zone and the Atlantic ‘collinean’ zone (terminology after Ozenda, 1975; Quezel, 1976). The former is characterised by the seral stage of Quercus pubescens, the latter by the seral stage of Quercus robur. The vegetal formation in the vicinity of the site consists of Quercus robur, Fraxinus excelsior, Acer
Fig. 1. Location of Troubat (Hautes Pyre´ne´es, France) and principal archaeological sites discussed in the text. 1: Troubat, 2: Margineda, 3: Gazel.
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campestre, Prunus avium, Populus tremula, Tilia parvifolia; among the shrubs, Corylus avellana is the most abundant with Cornus sanguinea, Crataegus oxyacantha, Prunus spinosa, Euonymus europaeus, Salix cinerea, Sorbus torminalis, Daphne laureola, Ligustrum vulgare and Hedera helix. Nearby, the river bank vegetation consists of Alnus glutinosa, Fraxinus excelsior, Populus nigra, Sambucus nigra, Corylus avellana, Cornus sanguinea, Tilia parvifolia. At about 700=900 m, deciduous oak is replaced by Fagus sylvatica, which marks the transition to the mountain zone; it is characterised by Fagus sylvatica and Abies alba. Finally, at about 1500–1700 m, we move into the subalpine zone with the seral stage of Pinus uncinata and then higher (2300=2400) into the alpine zone (Dupias, 1985). The site of Moulin (also known as Troubat) consists of a small cave with a cliff above which overhangs to form a shelter; the sheltered area provides the main archaeological levels. The excavation reopened access to a deep cave network, which had been obstructed by an accumulation of Azilian deposits. During the excavation, a distinction was made between the area of the shelter called the ‘external zone’ and the interior of the cave called the ‘internal zone’. The charcoal analysis was carried out only on material from the external zone.
3. Methods 3.1. Site sampling The site excavation was carried out by removing levels millimetres in thickness divided into square metres. The organisation of the excavation strove to favour observation of large areas in order to further the archaeoethnological approach. The intensity of the occupation often meant that in this type of ‘compressed’ stratigraphy, stratigraphical observation was particularly necessary. Systematic sampling of the charcoal and other materials was carried out by the square metre and by artificial layer; the sediments extracted during the archaeological excavation were systematically sieved with running water, with a mesh of 2 mm. The charcoal was thus exhaustively recovered. The charcoal concentrated in the archaeological struc-
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tures was treated separately from that scattered in the occupation levels. We will recall the conditions necessary for a palaeoecological study (Badal, 1990; Chabal, 1991; Heinz, 1990, 1991). (1) The charcoal should come from domestic firewood; building wood and worked wood were subjected to strong selection and are therefore not considered (Chabal, 1991, 1997). (2) Only charcoal from firewood, dispersed in the occupation levels, is taken into consideration in the palaeoecological study. That from archaeological structures (hearths, ditches, : : : ), representing brief events which provide low taxonomic diversity (last fire, last use) should be considered from a more archaeobotanical viewpoint and are not taken into account here. In fact, the charcoal from each period must represent a long period of activity. This is true of the charcoal scattered in the occupation levels. There is in fact a direct correlation between the duration of collection and the surface area sampled (Chabal, 1991). The minimum number of charcoal fragments is defined by the use of taxonomic curves; these present the number of taxa encountered during identification as a function of the number of charcoal fragments. It is a convenient criterion to determine at which point the optimal representation of taxa is obtained. The quantitative study consists of counting the fragments, each one constituting a unit whatever its size. Chabal (1991) notes that: “Whether the charcoal fragments are counted or weighed, their representation of the biomass is not necessarily the best”, neither of these taking into account the state of fragmentation. It has been demonstrated that there exists a positive linear correlation between number and mass, the law of fragmentation. The state of fragmentation observed in the archaeological material is independent of the taxon, consequently the relative frequencies can be estimated by weighing as well as by counting. In conclusion, the use of ‘numbers’ constitutes a practical unit, easy and rapid, which we use here.
4. Laboratory work The anatomical identification of the charcoal was carried out using a reflected light microscope with light and dark fields. The charcoal was frac-
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PLATE I
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tured by hand and the three anatomical planes of wood observed: transverse, longitudinal–tangential and longitudinal–radial. The observed structures were compared to those described in the atlas of wood anatomy (Metcalfe and Chalk, 1950, 1983; Greguss, 1955, 1959; Jacquiot, 1955; Jacquiot et al., 1973; Boureau, 1956; Schweingruber, 1978, 1990) and to a reference collection of modern charcoal. Some anatomical descriptions are necessary in order to justify certain taxonomic identifications. Furthermore, it is also useful to illustrate these identifications with photos of archaeological samples taken with an electron scanning microscope (S.E.M.) (Plates I–III). Concerning the genus Prunus, 3 types are distinguished; the first corresponds to fragments for which the woody rays are no wider than 2 cells. Type 2 is between 3 and 5 cells, and type 3 more than 5 cells. Taxonomically, type 1 might correspond to Prunus avium=padus, type 2 to Prunus spinosa=mahaleb, and type 3 to Prunus spinosa=amygdalus (Plate I). At least three species of Rhamnus were identified (Plates II and III): Rhamnus alpina, R. pumila, and R. cathartica=saxatilis. This is the first appearance of Rhamnus alpina and R. pumila in prehistoric charcoal. The width of the rays is the most reliable taxonomic criterion for distinguishing between them as well as the density of the pores in the early wood. Rhamnus pumila has rays which are extremely narrow (1 to 2 cells), Rhamnus cathartica=saxatilis has rays which are 3 to 5 cells wide with a pore density which is high in the early wood, and Rhamnus alpina has very large rays (5=6 to 8 cells). Finally the taxon Rhamnus sp. refers to fragments which are too small or in too bad a state of conservation for the width of the rays to be observed. In the case of Rhamnus pumila, reference is made to the anatomical structure of modern and archaeological carbonised samples (Plate II).
The junipers identified here have rays which, from an anatomical point of view, are very narrow (1 to 4 cells maximum), criteria which resemble Juniperus communis, J. thurifera, J. nana or even J. sabina (Plate II). The more thermophilic species J. oxycedrus, and J. phoenicea have rays which are 1 to 12 cells high, the average being 6.
5. Results 5.1. Archaeological data The stratigraphy presents an organised sedimentary sequence, without real continuity, in two principal units. The first series of deposits is made up of coarse sand probably of fluvio-glacial origin; the second series is represented by calcareous gravel from the ‘gre`ze’ type of scree which levels out the slope. The only clear rupture in the fill consists of a sterile alluvia-clay layer numbered ‘layer 9’. As the excavation advanced it became evident that this layer was limited to the area directly in line with the flow from the cave. The intensity of the occupation as well as probably the type of activity carried out on the site during different occupations caused these deposits to be laid down in an unequal fashion. It is these differences which are represented by the archaeological units presented here. Thirteen layers, which are subdivided into several levels, represent the remains of successive human occupations. These layers correspond to both relative and absolute dating as well as to the evidence provided by other Pyrenean sites in France and Spain. They date to between the 15th and 9th millennia B.P., according to radiocarbon dating. The archaeological studies provide evidence for three successive distinct phases. The first, still poorly understood (layers 13 to
PLATE I 1. 2. 3. 4. 5. 6.
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Prunus type 1, archaeological sample, transverse section (ð150). Prunus type 2, archaeological sample, transverse section (ð150). Prunus type 3, archaeological sample, transverse section (ð150). Rhamnus cathartica=saxatilis, archaeological sample, transverse section (ð100). Rhamnus alpina, archaeological sample, transverse section (ð100). Rhamnus alpina, archaeological sample, transverse section (ð400).
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PLATE II
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11), corresponds to a few brief and transitory occupations. The remains dispersed in low density produce thin archaeological levels which could simply amount to a floor used for circulation. Layer 13 probably corresponds to the base of the archaeological fill. The remains found within the mass of sedimentary deposits or spread out to form floors for occupation can be attributed to an early phase of the middle Magdalenian. The lithic objects from layer 11 date to late phases of the Magdalenian. So far only layer 12b (internal zone) has produced charcoal, a sample which is too limited to be considered here. The second phase (layers 10 to 6) consists of more intense occupation which was relatively longlasting. Hunting of large mammals was dominated by a preference for the ibex. This resource was complemented, according to the conditions of the environment during each period, by the hunting of reindeer, horses, aurochs, deer, boar, roe deer, goat, antelope : : : (H. Martin, unpublished). Fishing was well represented with the preponderant place being taken by salmonids, cyprinids, anguillids and esocids (O. Le Gall, unpublished). The upper Magdalenian is represented in layer 10 by a lithic industry which by its technology, morphology and typology fits into the same context as others found in the Pyrenees (Schmider, 1978; Sacchi, 1986). After a noticeable modification in the sedimentation (layer 9), the upper Magdalenian is still represented in layer 8 with features similar to those of the preceding Magdalenian horizon. Layer 7 is in stratigraphic continuity with the layer beneath. The bone and antler industry is still plentiful and clearly part of the Magdalenian tradition. This late Magdalenian, dated to the second half of the 11th millennium B.P. (C7b: Ly. 5272 — 11; 320 š 410 B.P.), is associated with a fauna which includes the first specimen of snails (Cepaea nemoralis).
Layer 6 is distinguished by its colour which is much darker than previous layers and sometimes even dark purplish brown. This phenomenon is probably due to the presence of organic remains, mainly carbon, as well as to impregnation by red pigments. It dates to the classic Pyrenean Azilian. This occupation has been dated to the first half of the 11th millennium (C6b: Ly. 5275 — 10; 770 š 100 B.P.). The third phase (layers 5 to 3) is characterised by snail collection, the principal activity for this period on the site. Human occupation is sparse, and the periods of occupation probably short, transitory, and repetitive. Layer 5 produced evidence of relatively rapid cultural changes. The Azilian culture is confirmed in C5c (Ly. 6405 — 9700 š 80 B.P.) by the lithic and bone industries, which are typically Pyrenean. The extraordinary quantity of snail shells (Cepaea nemoralis) in mounds transfigures the deposit. In C5b, this phenomenon is the result of human activity. The lithics collected on the upper surface of level C5c, those taken from levels C5b and C5a, as well as the absolute chronology, which place the middle level at the beginning of the 9th millennium (C5b: Ly. 5274 — 8890 š 75 B.P.), are in accordance with each other and date this phase to the middle Sauveterrian Montclusian (Barbaza, 1993). Layers 4, 3 and 2 contain approximately the same material as the two previous levels. Their stratigraphical position as well as the absolute chronology place their date of formation during the 9th millennium (C4: Ly. 5271 — 8880 š 75 B.P.). 5.2. Charcoal analysis data The absolute and relative frequencies of the taxa identified for each habitation level are indicated (Table 1) and presented in a charcoal diagram (Fig. 2). The vegetation dynamics observed in this diagram
PLATE II 1. 2. 3. 4. 5. 6.
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Rhamnus pumila, archaeological sample, transverse section (ð70). Rhamnus pumila, actual sample, transerve section (ð70) Rhamnus pumila, archaeological sample, transverse section (ð150). Rhamnus pumila, actual sample, transverse section (ð150). Juniperus sp., archaeological sample, transverse section (ð150). Hippophae rhamnoides, archaeological sample, tangential section (ð200).
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PLATE III
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clearly shows that the human populations collected all the woody plants available in their surroundings. The changes in plant cover revealed at Troubat can be divided into 4 phases, respectively called T1, T2, T3 and T4. Phase T1 contains the archaeological levels C10, C8c, C8a and C7b (Ly: 5272 — 11; 320 š 410 B.P.). From a palaeoecological point of view, phase T1 is characterised essentially by pioneer shrub species, with mountain and even subalpine affinities. Levels C8c, C8b, C8a, C7b are particularly interesting 1 rich in charcoal, they have produced many taxa (17 species in C8c, 15 for the other levels) and a fairly reliable quantification of the results (Fig. 2). Juniperus clearly predominates with Hippophae rhamnoides, Betula cf. verrucosa, Rhamnus alpina, Rhamnus pumila, Rhamnus cathartica=saxatilis, Prunus (type 1 and 2) and Salix sp. Pinus sylvestris appears in C8b and C7b; it is extremely rare. Concerning Juniperus, it could be J. communis, J. thurifera, J. nana or J. sabina; if all these pioneering species indicate a plant cover which is undergoing change, specific anatomical determinations would be very interesting from an ecological and biogeographical viewpoint.
1 The results obtained from charcoal associated directly with the archaeological structure of hearth type (F10) are included only in the frequency table (Table 1). The paucity of species in this hearth suggests transitory use. Only three taxa have been identified: Rhamnus pumila, Rhamnus alpina and Rhamnus sp. These taxa are present among the dispersed charcoal of C10. In the diagram all the data obtained from the dispersed charcoal are retained (Fig. 1) except for those from C10; in fact, the charcoal material is rare and only 43 fragments are of the dispersed type (C10). For this reason, we have decided that it is not useful to include these data in the charcoal diagram. Among the 7 taxa present are: Juniperus sp., Prunus type 1, 2 and 3 and Rhamnus alpina, R. pumila, R. cathartica=saxatilis, Rhamnus sp. The absolute frequencies of each are indicated (Table 1).
Juniperus communis is a pioneer species, very resistant to cold and drought, and develops at the present time in the ‘collinean’ zone at the base of the subalpine zone. At the present time the main area containing J. thurifera is found in the oro-Mediterranean zone of the central Iberian mountains and in southern Morocco. It also forms sizeable colonies in the southwestern Alps, the foothills of the Dauphine´ and one station in the central Pyrenees (region of St. Be´at). It is generally agreed that this is a survival of a thermophilic pre-glacial flora, which was maintained during the glaciations in rocky habitats (Ozenda, 1985). Juniperus nana and Juniperus sabina occur above the base of the subalpine zone; the first is associated with open forests with Pinus uncinata and with pioneer shrub associations with Juniperus communis, Rhamnus alpina, Amelanchier, Sorbus aria, Arctostaphylos uva-ursi at the base of the subalpine zone (Dupias, 1985), the second juniper is often found on rocks, dry grass and open forests with Pinus sylvestris and P. uncinata. Hippophae rhamnoides 2 a heliophyte, is a coloniser thanks to its adventitious suckering roots. It is found in open scrub pioneer associations on the edges of mountain streams. Betula verrucosa was identified from C8c; this is a pioneer species, very resistant to cold, capable of adaptation to all the substrata. To be noted is the significant presence of Rhamnus pumila, a low spreading shrub which is frequent in rocky habitats and in pioneer associations in the higher mountain and subalpine zone. Rhamnus alpina also develops in these contexts as well as in 2
No anatomical difference distinguishes H. rhamnoides ssp. fluviatilis from H. rhamnoides ssp. rhamnoides. However from a palaeoecological point of view, it is probably H. rhamnoides ssp. fluviatilis.
PLATE III 1. 2. 3. 4. 5. 6.
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Pinus sylvestris, archaeological sample, transverse section (ð60). Pinus sylvestris, archaeological sample, radial section (ð500). Betula verrucosa, archaeological sample, transverse section (ð100). Betula verrucosa, archaeological sample, radial section (ð400). Salix sp., archaeological sample, transverse section (ð100). Salix sp., archaeological sample, tangential section (ð250).
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Table 1 The site of Troubat (Hautes Pyre´ne´es): absolute and relative frequencies of taxa
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Fig. 2. Charcoal diagram analysis of Troubat (Hautes Pyre´ne´es, France).
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the mountain zone and even in the supra-Mediterranean zone. Moreover, concerning Rhamnus cathartica=saxatilis, R. saxatilis is a highly branched, prostrate shrub, being a xerophilous species, growing in halfshade or full sun, found up to the beginning of the mountain zone. Rhamnus cathartica is a heliophyte and calcicole and grows in open scrub pioneer associations but also in hygrophilous habitats. The four species of Prunus concerned are frequently associated with open environments (Prunus spinosa), with hygrophilous habitats (Prunus padus, Prunus avium), or again with the pioneer associations (Prunus padus, Prunus mahaleb). The identification of willow (Salix sp.) is to genus; despite the fact that several species of willow occur in very different biotopes (Rameau et al., 1993), they are all pioneering heliophytes. The occasional presence of Sambucus racemosa, Cornus sanguinea, Craetaegus, Sorbus and in C7b Corylus avellana (2 fragments) were noted. Viburnum lantana and V. opulus were identified. Although today these heliophytes or half-shade species tend to be found in hygrophilous habitats they are also present in the Rosaceae shrub associations. Thus, the abundance of Juniperus, of the Rosaceae (Prunus type 1, 2, 3), of Rhamnus alpina, R. cathartica=saxatilis, R. pumila, with Hippophae, Betula, Salix indicates an open environment and evokes a pioneer association in a climate of dry mountain or even subalpine type. A hygrophilous habitat was also in evidence with Cornus, Corylus, Viburnum, Sambucus. Two interrelated biotopes might have been exploited by man, i.e. the open hygrophilous habitat and most specially the hillsides covered with Juniperus pioneer associations 3 . These two habitats provided the catchment area for the wood gathered for fuel. During T1 (between about 13,000 B.P. and 11; 320 š 410 B.P.) a forest vegetation of Juniperus type became established in a dry mountain=subalpine climate during the general climatic amelioration. 3 Because of the ecological flexibility of the species, and identifications often only to genus level, it is impossible to relate each species to a single specific biotope. Thus, as we have noted above, certain Prunus, Rhamnus, Salix can be found in pioneer associations as well as in open hygrophilous habitats.
These changes are correlated with the Late Glacial interstadial, and C7b would even correspond to the interstadial forest optimum and its chronology in southern Europe (Beaulieu et al., 1982, 1988). Phase T2 includes levels C7a, C6b (Ly: 5275 — 10; 770 š 100 B.P.), C6a. It is characterised by a very clear decrease in Juniperus. The occurrence of Hippophae and Rhamnus pumila is diminished in C7 and disappears in C6b. Rhamnus alpina subsists and Betula is better represented than in T1. On the other hand, a rise in Rosaceae (Prunus type 1, Sorbus) and Rhamnus cathartica=saxatilis is clear. The curve of Pinus sylvestris although discreet is in slight progression from C6b onwards. The river bank plants become more abundant: Alnus, Daphne sp., as well as Viburnum, Sambucus, Cornus. From the classic Azilian levels C6b (10; 770š100 B.P.) and C6a onwards the first deciduous oaks are in evidence, accompanied by Acer type 1 (Acer cf. campestre) and by Corylus, already present in T1. The presence of a few fragments of deciduous Quercus correlates with the rapid development of this taxon at the beginning of the Holocene. As Beug (1975) has pointed out, the refugia of mesophilic trees were probably located in middle altitudes in ‘collinean’ situations less dry than the plains; then at the very beginning of the Holocene, the plains were the first to be colonised. The existence of Late Glacial refugia in the Pyrenean context has been demonstrated elsewhere (Jalut and Vernet, 1989; Andrieu, 1991; Reille and Andrieu, 1995). The appearance of deciduous Quercus in levels C6b and C6a at Troubat confirms the existence of these refugia. Thus, a reduction of the Juniperus pioneer association, which developed thanks to the Bo¨lling= Allero¨d warming, is observed; a transition phase to Rhamnus and Prunus follows. Some broad-leaved trees subsist. The rareness of Juniperus in C7a suggests a colder episode which would have taken place after 11; 320 š 410 B.P. This seems to appear at the beginning of the Younger Dryas. Thus the reduction of the Juniperus association together with an increase of Rhamnus and Rosaceae would be a response of the vegetation to the first cold periods. Between C6a (phase T2), and C5c (beginning of phase T3, Ly: 6405 — 9700 š 80 B.P.) in which the charcoal spectrum is typical of the beginning of the Post-Glacial, it is probable that there is a gap in
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the occupation of the shelter (external zone). At the beginning of the Post-Glacial, the curve of Quercus and Corylus in C5c indicates that the broad-leaved species that developed slightly in T1 survived during the Younger Dryas at a middle altitude. This is in accordance with the regional palynological data (Reille and Andrieu, 1995). The details of the stratigraphical sequence as well as the information it contains agree with this view which includes a gap in the occupation of the exterior part of the site where the charcoal sequence was established. The data recently acquired in the interior of the cave illustrate however that classic Azilian layer 6 was succeeded by an undifferentiated stratum revealing evidence from a later Azilian. It is thus possible that this sediment as a whole corresponds to deposits which were poorly represented in the exterior of the cave, and in fact indicate a connection which is at least partial between the remains of the extreme end of the upper Palaeolithic and the Mesolithic levels. The changes in the vegetation due to climate as seen in the charcoal diagram can be summarized thus: from phase T1 to T2, the change is from a period corresponding to the Late Glacial interstadial (Bo¨lling=Allero¨d) to a colder period (Younger Dryas). The Azilian levels C6b (Ly: 5275 — 10; 770 š 100 B.P.) and C6a would relate to this last cold period. From a chrono-cultural point of view, the date of 10; 770 š 100 B.P. is acceptable for the classic Azilian which several studies situate wholly or partly in the Younger Dryas (Girard et al., 1979). In the region of Cantabria, the period 11,000– 10,000, which was partly contemporary to the cold period of the Younger Dryas, is characterised by pioneering taxa (Uzquiano, 1995): Pinus, Juniperus, Betula. Deciduous oaks are also present. This cold episode, which palynologically is manifested by a rapid retreat of tree cover in favour of steppic herbaceous plants, but would still have allowed the growth of some trees and shrubs. Phase T3 consists of levels C5c (Ly: 6405 — 9700 š 80 B.P.), C5b (Ly: 5274 — 8890 š 75 B.P.), C5a, C4 (Ly: 5271 — 8880 š 75 B.P.). From 9700 š 80 B.P., the occurrence of Pinus sylvestris and above all that of deciduous Quercus is in progression, as well as that of Corylus. Rhamnus cathartica=saxatilis is in regression; Juniperus is
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very rare in C5c, and disappears in C5b; Sambucus is absent, Salix and Betula occasional. The hygrophilous forest includes Populus and Cornus. Viburnum disappears. It is possible that this heliophyte no longer found its optimal conditions in a gallery forest which was perhaps more closed. Thus a modification of environmental conditions took place associated with higher precipitation and temperatures, as indicated by this phase of forest colonisation by Corylus and the establishment of deciduous oak forests with Acer, Corylus, and Buxus. Prunus type 1 diminishes throughout T3, while Prunus type 2 remains constant; if this is Prunus mahaleb, it would appear to be part of the forest association with deciduous oak. As for Sorbus, it could easily be a composite curve in which several species are present; thus the progression of Sorbus in T3 could correspond to one or several species associated with the oak forest, perhaps S. aria or=and S. torminalis. In T1 and T2 there is mostly one specie related to an open mountain environment such as S. aucuparia. Moreover the malacological data reveal an abundance of snails (Cepaea nemoralis) for these levels and indicate ecological conditions particularly favourable for their development in large numbers (J. Andre´, unpublished). The deciduous oak forest definitively established in C4 forms a closed plant community; Pinus sylvestris (ca. 10%) is present nearby, at a somewhat higher altitude or as part of the oak forest. This forest vegetation is characteristic of the beginning of the Post-Glacial. The dominant plant association is then of ‘collinean’ type with some mountain influence, indicated by the presence of Pinus sylvestris. Then for levels C3c (Ly: 5273 — 8625 š 80 B.P.), C3b, C3a, C3c, C2a, the deciduous oak forest is established; this is phase T4. From level C3c onward, Pinus sylvestris and Corylus, both heliophytes, diminish in frequency, and this may indicate a progressively more dense forest environment.
6. Discussion The Balma Margineda (Guilaine and Martzluff, 1995) offers an interesting point of comparison with Troubat; it is situated at higher altitude (960 m) located in the supra-Mediterranean vegetation zone,
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in the valley of Andorra (Heinz, 1991; Heinz and Vernet, 1995). The MARG. 1 charcoal phase (about 11,500 to 10,700 B.P.) consists of Azilian levels; at the base the predominant plant associations are of dry mountain type, essentially pioneer plants, mainly pine forests with Pinus sylvestris but also open scrub associations with Juniperus, an heliophyte (Heinz, unpublished). The subalpine vegetation with Pinus uncinata is not far. At the edge of Valira, the persistence of mesophilic species is recorded: deciduous Quercus, Viburnum lantana, Corylus. This forest composition corresponds to the Late Glacial interstadial. The phase called MARG. 2, about 11,000 B.P., is characterised by a reduction of the Juniperus shrub association; the open Pinus sylvestris=Pinus uncinata forests persist. These events correspond to the first cool periods of the Younger Dryas. At 10; 640 š 260 BP, the maximal extension of the Pinus uncinata subalpine open forest is indicative of the coldest and driest phase of the whole sequence. MARG. 3 dates from the middle Mesolithic to the late Mesolithic, from about 9300 B.P. to 8500 B.P., and is characterised by the appearance of Abies alba, a marker of the humid mountain zone, and by the Juniperus optimum. Moreover, the frequency of Pinus sylvestris type is comparable to that of Pinus uncinata type. This indicates that the extreme subalpine conditions present up to this point are in the process of changing. It is a period when the climatic conditions appear more mountainous than subalpine. Phase MARG. 4 begins in the late Mesolithic (8210 š 180 B.P.): it is characterised by the expansion of deciduous Quercus, the regression of Pinus uncinata, the increase of Pinus sylvestris and a whole group of broad-leaved trees, Tilia, Ulmus, Sorbus, Crataegus, Betula, Buxus sempervirens, Hedera helix, Ilex aquifolium, Populus. The influence of the supra-Mediterranean oak forests in a mountain context is now clear. This phase is considered to be that of the Post-Glacial optimum. If the vegetation history of the forest discussed briefly here is synchronous from the point of view of the charcoal with that of Troubat, the subalpine aspects of the climate are more clearly expressed by the presence throughout the sequence of a Pinus uncinata open forest. The proximity of the mountain ranges, which culminate at about 3000 m in the
valley of Andorra, as well as the altitude of the site (960 m), are to be taken into account in order to understand these bioclimatic differences. The role played by Pinus sylvestris from 12,000 to 8000 B.P. is extremely reduced at Troubat if compared with the charcoal and pollen data for southern Europe. This is perhaps a local characteristic of the Garonnais piedmont (Andrieu, 1991). Recent palynological data obtained in the western Pyrenees also indicate the minor role of Pinus sylvestris (Reille and Andrieu, 1995). The palaeobotanical data from the cave ‘Les Eglises’ in Arie`ge from a level dated at 11; 800 š 500 BP also indicates the existence of pioneer species, Hippophae rhamnoides, Salix=Populus, and Juniperus (Bazile-Robert, 1983). The new results obtained at the Cauna de Gazel (alt. 240 m, Aude) resembling those first obtained by J.-L. Vernet (1980) for the epi-Magdalenian C7-C6, C6 (10; 760 š 190 BP) and Azilian (C4, C3) levels are also of interest here (Heinz, 1994, in press). The epi-Magdalenian layers (Sacchi, 1986) reveal a Pinus sylvestris open forest with Fabaceae and Juniperus. Betula and Salix are scarce, deciduous Quercus appears. Thus the Late Glacial interstadial favours the establishment of an open vegetation with Juniperus, Rhamnaceae and Rosaceae at Troubat (T1), heath land with Juniperus and Fabaceae at Gazel. About 10,700 B.P., at the first cold period of the Younger Dryas, Juniperus regresses, and Pinus and Fabaceae characterise the landscape while at Troubat, we see the retraction of the Juniperus scrub association and a phase with Rhamnus and Rosaceae. At Gazel, the Azilian levels of the PostGlacial, after 10,080 B.P., reveal the juxtaposition of two forest types: a Pinus sylvestris=Juniperus open forest and a deciduous oak forest (Quercus pubescens, Acer campestre, A. monspessulanum, Hedera, Corylus : : : ). At Troubat, phase T3 (from 9700 š 80 B.P.) clearly sees the establishment of deciduous oak forest. From the palynological viewpoint, the glaciolacustrine fill at Barbazan (450 m, central Pyrenees) has provided very precise data for the palaeoenvironment of the mountain valley of the Garonne from the end of the glacial period to the present (Andrieu, 1991; Reille and Andrieu, 1995). This site is very close to the cave-shelter of Moulin, and at a comparable altitude; this interdisciplinary work in-
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volving palynology, sedimentology and isotope data offers material for comparison. The tree species are particularly taken into account. The Late Glacial interstadial is palynologically marked by the beginning of the expansion of Juniperus and the rapid development of Poaceae. The progression of Juniperus is associated with that of Hippophae and Betula, and indicates the establishment of pioneer shrub associations near the site (Andrieu, 1991). Then a Juniperus optimum and the beginning of the expansion of Betula is noted at 12; 700 š 270 B.P. Finally, it is the strong progression of Betula and the modest success of Pinus which characterise, at Barbazan, the end of the Late Glacial interstadial. The optimum of the interstadial forest is dated at Barbazan to 11; 590 š 270 B.P. (Andrieu, 1991). At Troubat, the charcoal phase T1 corresponds to this optimum. The isotope data for the Bo¨lling–Allero¨d interstadial indicate a strong rise of δ18 O and of δ13 C related to a rapid warming of the climate during the phase of Juniperus colonising associations (Andrieu, 1991). The modest place of Pinus sylvestris in the pollen assemblages is surprising for a species which at the same period appears to characterise the pollen sequences of the northern Pyrenees (Jalut et al., 1982, 1988; Andrieu, 1987, 1991). The convergence of the pollen values with the charcoal data is thus clear: Pinus sylvestris probably played a reduced role in the Garonnais piedmont, in contrast to that which has been recorded, for example in Andorra (Heinz, 1991). Phase T2 is to be correlated to the climatic change of the Younger Dryas. At Barbazan, the palynology indicates an expansion of steppic plants. Juniperus, Hippophae and Rhamnus are also present. The trees Pinus and Betula are less well represented and indicate a more open environment. The isotope measurements carried out on the sediments coincide with a drop in temperature; the climatic characteristics of the Younger Dryas might have been analogous to those of the Older Dryas (Guiot, 1987; Guiot et al., 1989; Andrieu, 1991). Then at the beginning of the Post-Glacial, at about 10,300 B.P. if we consider the data for southern Europe (Beaulieu et al., 1982, 1988), a phase of expansion of deciduous Quercus on a regional scale is noted (Andrieu, 1991). The numerous palynological data obtained in the Pyrenees (Jalut, 1977; Jalut et al., 1982, 1988; Andrieu,
15
1991; Reille and Andrieu, 1995) testify to the simultaneous expansion of Quercus, at about 10,300 BP, throughout the northern slopes of the Pyrenees, from the West to the East. The start of this expansion marks the beginning of the Post-Glacial period. At Troubat, phase T3 is characterised by the very clear progression of Quercus and to a lesser extent that of Corylus from 9700 š 80 onwards. At about 8625 š 80 BP, the deciduous oak forest is established (phase T4). As the forest environment becomes progressively denser, heliophytes such as Pinus sylvestris and Corylus, diminish.
Acknowledgements We would like to thank Dr. Davis and Dr. Bottema for their useful criticisms, and suggestions. We are also grateful to Liz and George Willcox, and I. Figueiral for their help during the translation of this paper.
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pyre´ne´en au cours de l’Epipale´olithique et du Me´solithique. Actes du Ve`me congre`s international UISPP Epipale´olithique et Me´solithique en Europe, Grenoble (Ise`re, France). Heinz, C., Vernet, J.L., 1995. La Balma Margineda, analyses anthracologiques, l’homme et la ve´ge´tation in Les fouilles a` la Balma Margineda, sous la direction de J. Guilaine et M. Martzluff, Ministe`re des affaires sociales et culturelles du gouvernement d’Andorre, III, pp. 26–64. Jacquiot, C., 1955. Atlas d’anatomie des bois des conife`res. Centre Technique du Bois, Paris, 135 pp. Jacquiot, C., Trenard, Y., Dirol, D., 1973. Atlas d’anatomie des bois des Angiospermes. Centre Technique du Bois, Paris, 175 pp. Jalut, G., 1977. Ve´ge´tation et climat des Pyre´ne´es me´diterrane´ennes depuis quinze mille ans — Archives d’Ecologie pre´historique. Ecole des Hautes Etudes en Sciences Sociales Toulouse, 2, 141 pp. Jalut, G., Vernet, J.L., 1989. La ve´ge´tation du Pays de Sault et de ses marges depuis 15000 ans: re´interpre´tation des donne´es palynologiques et apports de l’anthracologie. In: Pays de sault, Espaces, Peuplements, Populations. Editions du CNRS, pp. 23–35. Jalut, G., Delibrias, G., Dagnac, J., Mardones, M., Bonhours, M., 1982. A palaeoecological approach to the last 21000 years in the Pyrenees: the peat bog of Freychinede (Alt. 1350 m, Arie`ge, south France). Palaeogeogr., Palaeoclimatol., Palaeoecol. 40, 321–359. Jalut, G., Andrieu, V., Delibrias, G., Fontugne, M., Pages, P., 1988. Paleoenvironment of the valley of Ossau (Western french Pyre´ne´es) during the last 27000 years. Pollen Spores 30 (1988), 357–394. Metcalfe, C.R., Chalk, L., 1950. Anatomy of the Dicotyledons. Clarendon Press, Oxford, 1500 pp. Metcalfe, C.R., Chalk, L., 1983. Anatomy of the Dicotyledons. Clarendon Press, Oxford, 297 pp. Ozenda, P., 1975. Sur les e´tages de ve´ge´tation dans les montagnes du bassin me´diterrane´en. Doc. de cartographie e´cologique, XVI, Grenoble, pp. 1–32. Ozenda, P., 1985. La ve´ge´tation de la chaıˆne alpine dans l’espace montagnard europe´en. Edition Masson, 330 pp. Quezel, P., 1976. Les foreˆts du pourtour me´diterane´en: e´cologie, conservation et ame´nagement. UNESCO, Notes Tech. M.A.B. 2, 9–33. Rameau, J.C., Mansion, D., Dume, G., Lecointe, A., Timbal, J., Dupont, P., Keller R., 1993. Flore forestie`re franc¸aise, guide e´cologique illustre´, I.D.F., 2, 2421 pp. Reille, M., Andrieu, V., 1995. The late Pleistocene and Holocene in the Lourdes Basin, Western Pyre´ne´es, France: new pollen analytical and chronological data. Veget. Hist. Archaeobot. 4, 1–21. Sacchi, D., 1986. Le Pale´olithique supe´rieur du Languedoc occidental et du Roussillon. XXIe suppl. Gallia Pre´histoire. Editions du CNRS, 284 pp. Schweingruber, F.H., 1978. Mikroskopische Holzanatomie. Zu¨rcher A.G. Zug, 226 pp. Schweingruber, F.H., 1990. Anatomie europa¨scher Ho¨lzer. Paul Haupt Bern und Stuttgart. 800 pp.
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83. Vernet, J.L., 1980. La ve´ge´tation du bassin de l’Aude, entre Pyre´ne´es et Massif central, au tardiglaciaire et au postglaciaire, d’apre`s l’analyse anthracologique. Rev. Palaeobot. Palynol. 30, 33–55.
Review of Palaeobotany and Palynology 104 (1998) 1–17
Environmental changes during the Late Glacial and Post-Glacial in the central Pyrenees (France): new charcoal analysis and archaeological data C. Heinz a,Ł , M. Barbaza b a
UPRESA 5059 of the CNRS, Laboratoire de Pale´oenvironnnements, Anthracologie, Action de l’Homme, Universite´ des Sciences et Techniques du Languedoc, Institut de Botanique, 163, rue Auguste Broussonet, 34090 Montpellier, France b UMR 5608 CNRS, Universite ´ , Culture, U.T.A.H. Laboratoire de Pre´histoire, Maison de la recherche, Universite´ de Toulouse-le-Mirail, 5 alle´es Antonio Machado, 31058 Toulouse cedex, France Received 16 January 1998; accepted 12 June 1998
Abstract The archaeological site at Troubat (Troubat, de´partment of Hautes Pyre´ne´es) has provided the first long charcoal sequence in the central Pyrenees. It offers information concerning the transformations in the vegetation cover due primarily to climate, from the Late Glacial Bo¨lling–Allero¨d interstadial to the middle of the Post-Glacial. Four main phases illustrate the changes in vegetation recorded in the charcoal data. Between about 13,000 B.P. and 11; 320 š 410 B.P. (phase T1) a vegetation with Juniperus, some Rosaceae (Prunus types 1, 2, 3), Rhamnus alpina, R. cathartica=saxatilis, R. pumila, Hippophae rhamnoides and Betula verrucosa is evidence of an open environment with colonising shrub cover established in a climate of dry mountain or even subalpine type. This change is correlated with the Late Glacial interstadial. At about 10; 770 š 100 B.P., a reduction of the Juniperus pioneer stage cover, which developed thanks to the Bo¨lling=Allero¨d warming, together with an increase of Rhamnus and Rosaceae, which would be a response of the vegetation to the first cooling of the Younger Dryas (phase T2). Around 9700 š 80 B.P., a phase of forest colonisation by Corylus and the establishment of deciduous oak forests which corresponds to the Post-Glacial climatic amelioration is noted (phase T3). Then, at about 8625 š 80 B.P., there is affirmation of an increase in deciduous oak forests of ‘collinean’ type. Pinus sylvestris, whose role is minor at Troubat, as well as Corylus, see their frequency diminish in response to an increasingly dense forest environment (phase T4). 1998 Elsevier Science B.V. All rights reserved. Keywords: charcoal analysis; archaeology; Late Glacial; Post-Glacial; central Pyrenees; Troubat; palaeoecology
1. Introduction The archaeological work carried out at the caveshelter of Moulin (Troubat, Haute-Pyre´ne´es) has provided an interesting and prodigious stratigraphy Ł Corresponding
author. Tel.: C33 4 9923-2180; Fax: C33 4 6754-3537; E-mail: [email protected]
concerning the period of the Late Glacial and the beginning of the Post-Glacial (Barbaza, 1988; Barbaza and Heinz, 1992). The long archaeological sequence, almost 4 metres, provides evidence of occupation with very little interruption from the middle Magdalenian (Magdalenian III of Breuil, between 16,000 B.P. and 15,000 B.P.) to the middle Sauveterrian Montclusian (between 9000 B.P. and 8000 B.P.). The
c 1998 Elsevier Science B.V. All rights reserved. 0034-6667/98/$19.00 PII: S 0 0 3 4 - 6 6 6 7 ( 9 8 ) 0 0 0 5 0 - 5
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C. Heinz, M. Barbaza / Review of Palaeobotany and Palynology 104 (1998) 1–17
abundance of charcoal as well systematic sampling have provided the first charcoal sequence for the central Pyrenees; almost 6000 fragments of carbonised wood have been studied. The species list consists of 37 trees, shrubs or bushes representing all the major forest species. Thus using this charcoal data we can trace the evolution of the plant cover and the changes in the vegetation over about 5000 years, from about 13,000 B.P. to 8000 B.P.
2. The site The cave shelter of Moulin at Troubat (HautesPyrenees) was formed in the Mesozoic limestone
which makes up the northern border of the Pyrenees (Fig. 1). It is situated at an altitude of 541 m near the Ourse basin in the region of the Garonnais piedmont. The valley of the Barousse consists of oceanic middle mountain landscapes. In the context of bioclimatic zones, it is a transition zone; the site itself located on the flank of the Gouade`re massif which rises to 800 m at the conjunction of the supra-Mediterranean vegetation zone and the Atlantic ‘collinean’ zone (terminology after Ozenda, 1975; Quezel, 1976). The former is characterised by the seral stage of Quercus pubescens, the latter by the seral stage of Quercus robur. The vegetal formation in the vicinity of the site consists of Quercus robur, Fraxinus excelsior, Acer
Fig. 1. Location of Troubat (Hautes Pyre´ne´es, France) and principal archaeological sites discussed in the text. 1: Troubat, 2: Margineda, 3: Gazel.
C. Heinz, M. Barbaza / Review of Palaeobotany and Palynology 104 (1998) 1–17
campestre, Prunus avium, Populus tremula, Tilia parvifolia; among the shrubs, Corylus avellana is the most abundant with Cornus sanguinea, Crataegus oxyacantha, Prunus spinosa, Euonymus europaeus, Salix cinerea, Sorbus torminalis, Daphne laureola, Ligustrum vulgare and Hedera helix. Nearby, the river bank vegetation consists of Alnus glutinosa, Fraxinus excelsior, Populus nigra, Sambucus nigra, Corylus avellana, Cornus sanguinea, Tilia parvifolia. At about 700=900 m, deciduous oak is replaced by Fagus sylvatica, which marks the transition to the mountain zone; it is characterised by Fagus sylvatica and Abies alba. Finally, at about 1500–1700 m, we move into the subalpine zone with the seral stage of Pinus uncinata and then higher (2300=2400) into the alpine zone (Dupias, 1985). The site of Moulin (also known as Troubat) consists of a small cave with a cliff above which overhangs to form a shelter; the sheltered area provides the main archaeological levels. The excavation reopened access to a deep cave network, which had been obstructed by an accumulation of Azilian deposits. During the excavation, a distinction was made between the area of the shelter called the ‘external zone’ and the interior of the cave called the ‘internal zone’. The charcoal analysis was carried out only on material from the external zone.
3. Methods 3.1. Site sampling The site excavation was carried out by removing levels millimetres in thickness divided into square metres. The organisation of the excavation strove to favour observation of large areas in order to further the archaeoethnological approach. The intensity of the occupation often meant that in this type of ‘compressed’ stratigraphy, stratigraphical observation was particularly necessary. Systematic sampling of the charcoal and other materials was carried out by the square metre and by artificial layer; the sediments extracted during the archaeological excavation were systematically sieved with running water, with a mesh of 2 mm. The charcoal was thus exhaustively recovered. The charcoal concentrated in the archaeological struc-
3
tures was treated separately from that scattered in the occupation levels. We will recall the conditions necessary for a palaeoecological study (Badal, 1990; Chabal, 1991; Heinz, 1990, 1991). (1) The charcoal should come from domestic firewood; building wood and worked wood were subjected to strong selection and are therefore not considered (Chabal, 1991, 1997). (2) Only charcoal from firewood, dispersed in the occupation levels, is taken into consideration in the palaeoecological study. That from archaeological structures (hearths, ditches, : : : ), representing brief events which provide low taxonomic diversity (last fire, last use) should be considered from a more archaeobotanical viewpoint and are not taken into account here. In fact, the charcoal from each period must represent a long period of activity. This is true of the charcoal scattered in the occupation levels. There is in fact a direct correlation between the duration of collection and the surface area sampled (Chabal, 1991). The minimum number of charcoal fragments is defined by the use of taxonomic curves; these present the number of taxa encountered during identification as a function of the number of charcoal fragments. It is a convenient criterion to determine at which point the optimal representation of taxa is obtained. The quantitative study consists of counting the fragments, each one constituting a unit whatever its size. Chabal (1991) notes that: “Whether the charcoal fragments are counted or weighed, their representation of the biomass is not necessarily the best”, neither of these taking into account the state of fragmentation. It has been demonstrated that there exists a positive linear correlation between number and mass, the law of fragmentation. The state of fragmentation observed in the archaeological material is independent of the taxon, consequently the relative frequencies can be estimated by weighing as well as by counting. In conclusion, the use of ‘numbers’ constitutes a practical unit, easy and rapid, which we use here.
4. Laboratory work The anatomical identification of the charcoal was carried out using a reflected light microscope with light and dark fields. The charcoal was frac-
4
PLATE I
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tured by hand and the three anatomical planes of wood observed: transverse, longitudinal–tangential and longitudinal–radial. The observed structures were compared to those described in the atlas of wood anatomy (Metcalfe and Chalk, 1950, 1983; Greguss, 1955, 1959; Jacquiot, 1955; Jacquiot et al., 1973; Boureau, 1956; Schweingruber, 1978, 1990) and to a reference collection of modern charcoal. Some anatomical descriptions are necessary in order to justify certain taxonomic identifications. Furthermore, it is also useful to illustrate these identifications with photos of archaeological samples taken with an electron scanning microscope (S.E.M.) (Plates I–III). Concerning the genus Prunus, 3 types are distinguished; the first corresponds to fragments for which the woody rays are no wider than 2 cells. Type 2 is between 3 and 5 cells, and type 3 more than 5 cells. Taxonomically, type 1 might correspond to Prunus avium=padus, type 2 to Prunus spinosa=mahaleb, and type 3 to Prunus spinosa=amygdalus (Plate I). At least three species of Rhamnus were identified (Plates II and III): Rhamnus alpina, R. pumila, and R. cathartica=saxatilis. This is the first appearance of Rhamnus alpina and R. pumila in prehistoric charcoal. The width of the rays is the most reliable taxonomic criterion for distinguishing between them as well as the density of the pores in the early wood. Rhamnus pumila has rays which are extremely narrow (1 to 2 cells), Rhamnus cathartica=saxatilis has rays which are 3 to 5 cells wide with a pore density which is high in the early wood, and Rhamnus alpina has very large rays (5=6 to 8 cells). Finally the taxon Rhamnus sp. refers to fragments which are too small or in too bad a state of conservation for the width of the rays to be observed. In the case of Rhamnus pumila, reference is made to the anatomical structure of modern and archaeological carbonised samples (Plate II).
The junipers identified here have rays which, from an anatomical point of view, are very narrow (1 to 4 cells maximum), criteria which resemble Juniperus communis, J. thurifera, J. nana or even J. sabina (Plate II). The more thermophilic species J. oxycedrus, and J. phoenicea have rays which are 1 to 12 cells high, the average being 6.
5. Results 5.1. Archaeological data The stratigraphy presents an organised sedimentary sequence, without real continuity, in two principal units. The first series of deposits is made up of coarse sand probably of fluvio-glacial origin; the second series is represented by calcareous gravel from the ‘gre`ze’ type of scree which levels out the slope. The only clear rupture in the fill consists of a sterile alluvia-clay layer numbered ‘layer 9’. As the excavation advanced it became evident that this layer was limited to the area directly in line with the flow from the cave. The intensity of the occupation as well as probably the type of activity carried out on the site during different occupations caused these deposits to be laid down in an unequal fashion. It is these differences which are represented by the archaeological units presented here. Thirteen layers, which are subdivided into several levels, represent the remains of successive human occupations. These layers correspond to both relative and absolute dating as well as to the evidence provided by other Pyrenean sites in France and Spain. They date to between the 15th and 9th millennia B.P., according to radiocarbon dating. The archaeological studies provide evidence for three successive distinct phases. The first, still poorly understood (layers 13 to
PLATE I 1. 2. 3. 4. 5. 6.
5
Prunus type 1, archaeological sample, transverse section (ð150). Prunus type 2, archaeological sample, transverse section (ð150). Prunus type 3, archaeological sample, transverse section (ð150). Rhamnus cathartica=saxatilis, archaeological sample, transverse section (ð100). Rhamnus alpina, archaeological sample, transverse section (ð100). Rhamnus alpina, archaeological sample, transverse section (ð400).
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PLATE II
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11), corresponds to a few brief and transitory occupations. The remains dispersed in low density produce thin archaeological levels which could simply amount to a floor used for circulation. Layer 13 probably corresponds to the base of the archaeological fill. The remains found within the mass of sedimentary deposits or spread out to form floors for occupation can be attributed to an early phase of the middle Magdalenian. The lithic objects from layer 11 date to late phases of the Magdalenian. So far only layer 12b (internal zone) has produced charcoal, a sample which is too limited to be considered here. The second phase (layers 10 to 6) consists of more intense occupation which was relatively longlasting. Hunting of large mammals was dominated by a preference for the ibex. This resource was complemented, according to the conditions of the environment during each period, by the hunting of reindeer, horses, aurochs, deer, boar, roe deer, goat, antelope : : : (H. Martin, unpublished). Fishing was well represented with the preponderant place being taken by salmonids, cyprinids, anguillids and esocids (O. Le Gall, unpublished). The upper Magdalenian is represented in layer 10 by a lithic industry which by its technology, morphology and typology fits into the same context as others found in the Pyrenees (Schmider, 1978; Sacchi, 1986). After a noticeable modification in the sedimentation (layer 9), the upper Magdalenian is still represented in layer 8 with features similar to those of the preceding Magdalenian horizon. Layer 7 is in stratigraphic continuity with the layer beneath. The bone and antler industry is still plentiful and clearly part of the Magdalenian tradition. This late Magdalenian, dated to the second half of the 11th millennium B.P. (C7b: Ly. 5272 — 11; 320 š 410 B.P.), is associated with a fauna which includes the first specimen of snails (Cepaea nemoralis).
Layer 6 is distinguished by its colour which is much darker than previous layers and sometimes even dark purplish brown. This phenomenon is probably due to the presence of organic remains, mainly carbon, as well as to impregnation by red pigments. It dates to the classic Pyrenean Azilian. This occupation has been dated to the first half of the 11th millennium (C6b: Ly. 5275 — 10; 770 š 100 B.P.). The third phase (layers 5 to 3) is characterised by snail collection, the principal activity for this period on the site. Human occupation is sparse, and the periods of occupation probably short, transitory, and repetitive. Layer 5 produced evidence of relatively rapid cultural changes. The Azilian culture is confirmed in C5c (Ly. 6405 — 9700 š 80 B.P.) by the lithic and bone industries, which are typically Pyrenean. The extraordinary quantity of snail shells (Cepaea nemoralis) in mounds transfigures the deposit. In C5b, this phenomenon is the result of human activity. The lithics collected on the upper surface of level C5c, those taken from levels C5b and C5a, as well as the absolute chronology, which place the middle level at the beginning of the 9th millennium (C5b: Ly. 5274 — 8890 š 75 B.P.), are in accordance with each other and date this phase to the middle Sauveterrian Montclusian (Barbaza, 1993). Layers 4, 3 and 2 contain approximately the same material as the two previous levels. Their stratigraphical position as well as the absolute chronology place their date of formation during the 9th millennium (C4: Ly. 5271 — 8880 š 75 B.P.). 5.2. Charcoal analysis data The absolute and relative frequencies of the taxa identified for each habitation level are indicated (Table 1) and presented in a charcoal diagram (Fig. 2). The vegetation dynamics observed in this diagram
PLATE II 1. 2. 3. 4. 5. 6.
7
Rhamnus pumila, archaeological sample, transverse section (ð70). Rhamnus pumila, actual sample, transerve section (ð70) Rhamnus pumila, archaeological sample, transverse section (ð150). Rhamnus pumila, actual sample, transverse section (ð150). Juniperus sp., archaeological sample, transverse section (ð150). Hippophae rhamnoides, archaeological sample, tangential section (ð200).
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PLATE III
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clearly shows that the human populations collected all the woody plants available in their surroundings. The changes in plant cover revealed at Troubat can be divided into 4 phases, respectively called T1, T2, T3 and T4. Phase T1 contains the archaeological levels C10, C8c, C8a and C7b (Ly: 5272 — 11; 320 š 410 B.P.). From a palaeoecological point of view, phase T1 is characterised essentially by pioneer shrub species, with mountain and even subalpine affinities. Levels C8c, C8b, C8a, C7b are particularly interesting 1 rich in charcoal, they have produced many taxa (17 species in C8c, 15 for the other levels) and a fairly reliable quantification of the results (Fig. 2). Juniperus clearly predominates with Hippophae rhamnoides, Betula cf. verrucosa, Rhamnus alpina, Rhamnus pumila, Rhamnus cathartica=saxatilis, Prunus (type 1 and 2) and Salix sp. Pinus sylvestris appears in C8b and C7b; it is extremely rare. Concerning Juniperus, it could be J. communis, J. thurifera, J. nana or J. sabina; if all these pioneering species indicate a plant cover which is undergoing change, specific anatomical determinations would be very interesting from an ecological and biogeographical viewpoint.
1 The results obtained from charcoal associated directly with the archaeological structure of hearth type (F10) are included only in the frequency table (Table 1). The paucity of species in this hearth suggests transitory use. Only three taxa have been identified: Rhamnus pumila, Rhamnus alpina and Rhamnus sp. These taxa are present among the dispersed charcoal of C10. In the diagram all the data obtained from the dispersed charcoal are retained (Fig. 1) except for those from C10; in fact, the charcoal material is rare and only 43 fragments are of the dispersed type (C10). For this reason, we have decided that it is not useful to include these data in the charcoal diagram. Among the 7 taxa present are: Juniperus sp., Prunus type 1, 2 and 3 and Rhamnus alpina, R. pumila, R. cathartica=saxatilis, Rhamnus sp. The absolute frequencies of each are indicated (Table 1).
Juniperus communis is a pioneer species, very resistant to cold and drought, and develops at the present time in the ‘collinean’ zone at the base of the subalpine zone. At the present time the main area containing J. thurifera is found in the oro-Mediterranean zone of the central Iberian mountains and in southern Morocco. It also forms sizeable colonies in the southwestern Alps, the foothills of the Dauphine´ and one station in the central Pyrenees (region of St. Be´at). It is generally agreed that this is a survival of a thermophilic pre-glacial flora, which was maintained during the glaciations in rocky habitats (Ozenda, 1985). Juniperus nana and Juniperus sabina occur above the base of the subalpine zone; the first is associated with open forests with Pinus uncinata and with pioneer shrub associations with Juniperus communis, Rhamnus alpina, Amelanchier, Sorbus aria, Arctostaphylos uva-ursi at the base of the subalpine zone (Dupias, 1985), the second juniper is often found on rocks, dry grass and open forests with Pinus sylvestris and P. uncinata. Hippophae rhamnoides 2 a heliophyte, is a coloniser thanks to its adventitious suckering roots. It is found in open scrub pioneer associations on the edges of mountain streams. Betula verrucosa was identified from C8c; this is a pioneer species, very resistant to cold, capable of adaptation to all the substrata. To be noted is the significant presence of Rhamnus pumila, a low spreading shrub which is frequent in rocky habitats and in pioneer associations in the higher mountain and subalpine zone. Rhamnus alpina also develops in these contexts as well as in 2
No anatomical difference distinguishes H. rhamnoides ssp. fluviatilis from H. rhamnoides ssp. rhamnoides. However from a palaeoecological point of view, it is probably H. rhamnoides ssp. fluviatilis.
PLATE III 1. 2. 3. 4. 5. 6.
9
Pinus sylvestris, archaeological sample, transverse section (ð60). Pinus sylvestris, archaeological sample, radial section (ð500). Betula verrucosa, archaeological sample, transverse section (ð100). Betula verrucosa, archaeological sample, radial section (ð400). Salix sp., archaeological sample, transverse section (ð100). Salix sp., archaeological sample, tangential section (ð250).
10
Table 1 The site of Troubat (Hautes Pyre´ne´es): absolute and relative frequencies of taxa
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Fig. 2. Charcoal diagram analysis of Troubat (Hautes Pyre´ne´es, France).
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the mountain zone and even in the supra-Mediterranean zone. Moreover, concerning Rhamnus cathartica=saxatilis, R. saxatilis is a highly branched, prostrate shrub, being a xerophilous species, growing in halfshade or full sun, found up to the beginning of the mountain zone. Rhamnus cathartica is a heliophyte and calcicole and grows in open scrub pioneer associations but also in hygrophilous habitats. The four species of Prunus concerned are frequently associated with open environments (Prunus spinosa), with hygrophilous habitats (Prunus padus, Prunus avium), or again with the pioneer associations (Prunus padus, Prunus mahaleb). The identification of willow (Salix sp.) is to genus; despite the fact that several species of willow occur in very different biotopes (Rameau et al., 1993), they are all pioneering heliophytes. The occasional presence of Sambucus racemosa, Cornus sanguinea, Craetaegus, Sorbus and in C7b Corylus avellana (2 fragments) were noted. Viburnum lantana and V. opulus were identified. Although today these heliophytes or half-shade species tend to be found in hygrophilous habitats they are also present in the Rosaceae shrub associations. Thus, the abundance of Juniperus, of the Rosaceae (Prunus type 1, 2, 3), of Rhamnus alpina, R. cathartica=saxatilis, R. pumila, with Hippophae, Betula, Salix indicates an open environment and evokes a pioneer association in a climate of dry mountain or even subalpine type. A hygrophilous habitat was also in evidence with Cornus, Corylus, Viburnum, Sambucus. Two interrelated biotopes might have been exploited by man, i.e. the open hygrophilous habitat and most specially the hillsides covered with Juniperus pioneer associations 3 . These two habitats provided the catchment area for the wood gathered for fuel. During T1 (between about 13,000 B.P. and 11; 320 š 410 B.P.) a forest vegetation of Juniperus type became established in a dry mountain=subalpine climate during the general climatic amelioration. 3 Because of the ecological flexibility of the species, and identifications often only to genus level, it is impossible to relate each species to a single specific biotope. Thus, as we have noted above, certain Prunus, Rhamnus, Salix can be found in pioneer associations as well as in open hygrophilous habitats.
These changes are correlated with the Late Glacial interstadial, and C7b would even correspond to the interstadial forest optimum and its chronology in southern Europe (Beaulieu et al., 1982, 1988). Phase T2 includes levels C7a, C6b (Ly: 5275 — 10; 770 š 100 B.P.), C6a. It is characterised by a very clear decrease in Juniperus. The occurrence of Hippophae and Rhamnus pumila is diminished in C7 and disappears in C6b. Rhamnus alpina subsists and Betula is better represented than in T1. On the other hand, a rise in Rosaceae (Prunus type 1, Sorbus) and Rhamnus cathartica=saxatilis is clear. The curve of Pinus sylvestris although discreet is in slight progression from C6b onwards. The river bank plants become more abundant: Alnus, Daphne sp., as well as Viburnum, Sambucus, Cornus. From the classic Azilian levels C6b (10; 770š100 B.P.) and C6a onwards the first deciduous oaks are in evidence, accompanied by Acer type 1 (Acer cf. campestre) and by Corylus, already present in T1. The presence of a few fragments of deciduous Quercus correlates with the rapid development of this taxon at the beginning of the Holocene. As Beug (1975) has pointed out, the refugia of mesophilic trees were probably located in middle altitudes in ‘collinean’ situations less dry than the plains; then at the very beginning of the Holocene, the plains were the first to be colonised. The existence of Late Glacial refugia in the Pyrenean context has been demonstrated elsewhere (Jalut and Vernet, 1989; Andrieu, 1991; Reille and Andrieu, 1995). The appearance of deciduous Quercus in levels C6b and C6a at Troubat confirms the existence of these refugia. Thus, a reduction of the Juniperus pioneer association, which developed thanks to the Bo¨lling= Allero¨d warming, is observed; a transition phase to Rhamnus and Prunus follows. Some broad-leaved trees subsist. The rareness of Juniperus in C7a suggests a colder episode which would have taken place after 11; 320 š 410 B.P. This seems to appear at the beginning of the Younger Dryas. Thus the reduction of the Juniperus association together with an increase of Rhamnus and Rosaceae would be a response of the vegetation to the first cold periods. Between C6a (phase T2), and C5c (beginning of phase T3, Ly: 6405 — 9700 š 80 B.P.) in which the charcoal spectrum is typical of the beginning of the Post-Glacial, it is probable that there is a gap in
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the occupation of the shelter (external zone). At the beginning of the Post-Glacial, the curve of Quercus and Corylus in C5c indicates that the broad-leaved species that developed slightly in T1 survived during the Younger Dryas at a middle altitude. This is in accordance with the regional palynological data (Reille and Andrieu, 1995). The details of the stratigraphical sequence as well as the information it contains agree with this view which includes a gap in the occupation of the exterior part of the site where the charcoal sequence was established. The data recently acquired in the interior of the cave illustrate however that classic Azilian layer 6 was succeeded by an undifferentiated stratum revealing evidence from a later Azilian. It is thus possible that this sediment as a whole corresponds to deposits which were poorly represented in the exterior of the cave, and in fact indicate a connection which is at least partial between the remains of the extreme end of the upper Palaeolithic and the Mesolithic levels. The changes in the vegetation due to climate as seen in the charcoal diagram can be summarized thus: from phase T1 to T2, the change is from a period corresponding to the Late Glacial interstadial (Bo¨lling=Allero¨d) to a colder period (Younger Dryas). The Azilian levels C6b (Ly: 5275 — 10; 770 š 100 B.P.) and C6a would relate to this last cold period. From a chrono-cultural point of view, the date of 10; 770 š 100 B.P. is acceptable for the classic Azilian which several studies situate wholly or partly in the Younger Dryas (Girard et al., 1979). In the region of Cantabria, the period 11,000– 10,000, which was partly contemporary to the cold period of the Younger Dryas, is characterised by pioneering taxa (Uzquiano, 1995): Pinus, Juniperus, Betula. Deciduous oaks are also present. This cold episode, which palynologically is manifested by a rapid retreat of tree cover in favour of steppic herbaceous plants, but would still have allowed the growth of some trees and shrubs. Phase T3 consists of levels C5c (Ly: 6405 — 9700 š 80 B.P.), C5b (Ly: 5274 — 8890 š 75 B.P.), C5a, C4 (Ly: 5271 — 8880 š 75 B.P.). From 9700 š 80 B.P., the occurrence of Pinus sylvestris and above all that of deciduous Quercus is in progression, as well as that of Corylus. Rhamnus cathartica=saxatilis is in regression; Juniperus is
13
very rare in C5c, and disappears in C5b; Sambucus is absent, Salix and Betula occasional. The hygrophilous forest includes Populus and Cornus. Viburnum disappears. It is possible that this heliophyte no longer found its optimal conditions in a gallery forest which was perhaps more closed. Thus a modification of environmental conditions took place associated with higher precipitation and temperatures, as indicated by this phase of forest colonisation by Corylus and the establishment of deciduous oak forests with Acer, Corylus, and Buxus. Prunus type 1 diminishes throughout T3, while Prunus type 2 remains constant; if this is Prunus mahaleb, it would appear to be part of the forest association with deciduous oak. As for Sorbus, it could easily be a composite curve in which several species are present; thus the progression of Sorbus in T3 could correspond to one or several species associated with the oak forest, perhaps S. aria or=and S. torminalis. In T1 and T2 there is mostly one specie related to an open mountain environment such as S. aucuparia. Moreover the malacological data reveal an abundance of snails (Cepaea nemoralis) for these levels and indicate ecological conditions particularly favourable for their development in large numbers (J. Andre´, unpublished). The deciduous oak forest definitively established in C4 forms a closed plant community; Pinus sylvestris (ca. 10%) is present nearby, at a somewhat higher altitude or as part of the oak forest. This forest vegetation is characteristic of the beginning of the Post-Glacial. The dominant plant association is then of ‘collinean’ type with some mountain influence, indicated by the presence of Pinus sylvestris. Then for levels C3c (Ly: 5273 — 8625 š 80 B.P.), C3b, C3a, C3c, C2a, the deciduous oak forest is established; this is phase T4. From level C3c onward, Pinus sylvestris and Corylus, both heliophytes, diminish in frequency, and this may indicate a progressively more dense forest environment.
6. Discussion The Balma Margineda (Guilaine and Martzluff, 1995) offers an interesting point of comparison with Troubat; it is situated at higher altitude (960 m) located in the supra-Mediterranean vegetation zone,
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in the valley of Andorra (Heinz, 1991; Heinz and Vernet, 1995). The MARG. 1 charcoal phase (about 11,500 to 10,700 B.P.) consists of Azilian levels; at the base the predominant plant associations are of dry mountain type, essentially pioneer plants, mainly pine forests with Pinus sylvestris but also open scrub associations with Juniperus, an heliophyte (Heinz, unpublished). The subalpine vegetation with Pinus uncinata is not far. At the edge of Valira, the persistence of mesophilic species is recorded: deciduous Quercus, Viburnum lantana, Corylus. This forest composition corresponds to the Late Glacial interstadial. The phase called MARG. 2, about 11,000 B.P., is characterised by a reduction of the Juniperus shrub association; the open Pinus sylvestris=Pinus uncinata forests persist. These events correspond to the first cool periods of the Younger Dryas. At 10; 640 š 260 BP, the maximal extension of the Pinus uncinata subalpine open forest is indicative of the coldest and driest phase of the whole sequence. MARG. 3 dates from the middle Mesolithic to the late Mesolithic, from about 9300 B.P. to 8500 B.P., and is characterised by the appearance of Abies alba, a marker of the humid mountain zone, and by the Juniperus optimum. Moreover, the frequency of Pinus sylvestris type is comparable to that of Pinus uncinata type. This indicates that the extreme subalpine conditions present up to this point are in the process of changing. It is a period when the climatic conditions appear more mountainous than subalpine. Phase MARG. 4 begins in the late Mesolithic (8210 š 180 B.P.): it is characterised by the expansion of deciduous Quercus, the regression of Pinus uncinata, the increase of Pinus sylvestris and a whole group of broad-leaved trees, Tilia, Ulmus, Sorbus, Crataegus, Betula, Buxus sempervirens, Hedera helix, Ilex aquifolium, Populus. The influence of the supra-Mediterranean oak forests in a mountain context is now clear. This phase is considered to be that of the Post-Glacial optimum. If the vegetation history of the forest discussed briefly here is synchronous from the point of view of the charcoal with that of Troubat, the subalpine aspects of the climate are more clearly expressed by the presence throughout the sequence of a Pinus uncinata open forest. The proximity of the mountain ranges, which culminate at about 3000 m in the
valley of Andorra, as well as the altitude of the site (960 m), are to be taken into account in order to understand these bioclimatic differences. The role played by Pinus sylvestris from 12,000 to 8000 B.P. is extremely reduced at Troubat if compared with the charcoal and pollen data for southern Europe. This is perhaps a local characteristic of the Garonnais piedmont (Andrieu, 1991). Recent palynological data obtained in the western Pyrenees also indicate the minor role of Pinus sylvestris (Reille and Andrieu, 1995). The palaeobotanical data from the cave ‘Les Eglises’ in Arie`ge from a level dated at 11; 800 š 500 BP also indicates the existence of pioneer species, Hippophae rhamnoides, Salix=Populus, and Juniperus (Bazile-Robert, 1983). The new results obtained at the Cauna de Gazel (alt. 240 m, Aude) resembling those first obtained by J.-L. Vernet (1980) for the epi-Magdalenian C7-C6, C6 (10; 760 š 190 BP) and Azilian (C4, C3) levels are also of interest here (Heinz, 1994, in press). The epi-Magdalenian layers (Sacchi, 1986) reveal a Pinus sylvestris open forest with Fabaceae and Juniperus. Betula and Salix are scarce, deciduous Quercus appears. Thus the Late Glacial interstadial favours the establishment of an open vegetation with Juniperus, Rhamnaceae and Rosaceae at Troubat (T1), heath land with Juniperus and Fabaceae at Gazel. About 10,700 B.P., at the first cold period of the Younger Dryas, Juniperus regresses, and Pinus and Fabaceae characterise the landscape while at Troubat, we see the retraction of the Juniperus scrub association and a phase with Rhamnus and Rosaceae. At Gazel, the Azilian levels of the PostGlacial, after 10,080 B.P., reveal the juxtaposition of two forest types: a Pinus sylvestris=Juniperus open forest and a deciduous oak forest (Quercus pubescens, Acer campestre, A. monspessulanum, Hedera, Corylus : : : ). At Troubat, phase T3 (from 9700 š 80 B.P.) clearly sees the establishment of deciduous oak forest. From the palynological viewpoint, the glaciolacustrine fill at Barbazan (450 m, central Pyrenees) has provided very precise data for the palaeoenvironment of the mountain valley of the Garonne from the end of the glacial period to the present (Andrieu, 1991; Reille and Andrieu, 1995). This site is very close to the cave-shelter of Moulin, and at a comparable altitude; this interdisciplinary work in-
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volving palynology, sedimentology and isotope data offers material for comparison. The tree species are particularly taken into account. The Late Glacial interstadial is palynologically marked by the beginning of the expansion of Juniperus and the rapid development of Poaceae. The progression of Juniperus is associated with that of Hippophae and Betula, and indicates the establishment of pioneer shrub associations near the site (Andrieu, 1991). Then a Juniperus optimum and the beginning of the expansion of Betula is noted at 12; 700 š 270 B.P. Finally, it is the strong progression of Betula and the modest success of Pinus which characterise, at Barbazan, the end of the Late Glacial interstadial. The optimum of the interstadial forest is dated at Barbazan to 11; 590 š 270 B.P. (Andrieu, 1991). At Troubat, the charcoal phase T1 corresponds to this optimum. The isotope data for the Bo¨lling–Allero¨d interstadial indicate a strong rise of δ18 O and of δ13 C related to a rapid warming of the climate during the phase of Juniperus colonising associations (Andrieu, 1991). The modest place of Pinus sylvestris in the pollen assemblages is surprising for a species which at the same period appears to characterise the pollen sequences of the northern Pyrenees (Jalut et al., 1982, 1988; Andrieu, 1987, 1991). The convergence of the pollen values with the charcoal data is thus clear: Pinus sylvestris probably played a reduced role in the Garonnais piedmont, in contrast to that which has been recorded, for example in Andorra (Heinz, 1991). Phase T2 is to be correlated to the climatic change of the Younger Dryas. At Barbazan, the palynology indicates an expansion of steppic plants. Juniperus, Hippophae and Rhamnus are also present. The trees Pinus and Betula are less well represented and indicate a more open environment. The isotope measurements carried out on the sediments coincide with a drop in temperature; the climatic characteristics of the Younger Dryas might have been analogous to those of the Older Dryas (Guiot, 1987; Guiot et al., 1989; Andrieu, 1991). Then at the beginning of the Post-Glacial, at about 10,300 B.P. if we consider the data for southern Europe (Beaulieu et al., 1982, 1988), a phase of expansion of deciduous Quercus on a regional scale is noted (Andrieu, 1991). The numerous palynological data obtained in the Pyrenees (Jalut, 1977; Jalut et al., 1982, 1988; Andrieu,
15
1991; Reille and Andrieu, 1995) testify to the simultaneous expansion of Quercus, at about 10,300 BP, throughout the northern slopes of the Pyrenees, from the West to the East. The start of this expansion marks the beginning of the Post-Glacial period. At Troubat, phase T3 is characterised by the very clear progression of Quercus and to a lesser extent that of Corylus from 9700 š 80 onwards. At about 8625 š 80 BP, the deciduous oak forest is established (phase T4). As the forest environment becomes progressively denser, heliophytes such as Pinus sylvestris and Corylus, diminish.
Acknowledgements We would like to thank Dr. Davis and Dr. Bottema for their useful criticisms, and suggestions. We are also grateful to Liz and George Willcox, and I. Figueiral for their help during the translation of this paper.
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