Holocene Vegetation, Landscape And
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Quaternaire, 22, (2), 2011, p. 147-164 HOLOCENE VEGETATION, LANDSCAPE AND RECONSTRUCTION OF HUMAN ACTIVITY FROM PREHISTORY TO THE ROMAN PERIOD BASED ON NEW POLLEN DATA PERFORMED IN “THE PLATEAU DE MILLEVACHES” (LIMOUSIN, MASSIF CENTRAL, FRANCE) n Yannick MIRAS1,2, Pascal GUENET3 & Hervé RICHARD3 ABSTRACT New pollen analyses from four peat bogs and fens located on the plateau de Millevaches (Limousin, French Massif Central) are compared with one peat sequence situated at lower altitude in the northern Limousin (Mont d’Ambazac). This study, which is supported by eleven accepted AMS radiocarbon data, was undertaken to consider changes in regional vegetation from the beginning of the Holocene and to provide a first reconstruction of land-use history. A singular vegetation history characterizes the “plateau de Millevaches” from the center of the French Massif Central such as the simultaneous start of Corylus and Quercus dated from ca. 10560-10150 cal. BP (ca. 8550-8200 cal. BC). The composition of the forest cover remained largely unchanged with a large su- premacy of Corylus in the regional vegetation until ca. 8050-7650 cal. BP (ca. 6100-5700 cal. BC) when the decline of Corylus was synchronous with the expansion of Quercus. The diversifiedoak woodlands were rapidly filledb y Tilia, and pollen data indicate early Neolithic farming around 6600-6500 cal. BP (ca. 4600-4500 cal. BC). The installation of Fagus, which is dated about 5660-5300 cal. BP (ca. 3700-3400 cal. BC), occurs nearly 700 years later than in neighbouring Auvergne. The firstoak and beech forests spread after ca. 4800-4400 cal. BP (ca. 2850-2450 cal. BC), and Fagus constitutes the dominant arboreal taxa in the regional vegetation only since ca. 3900-3550 cal. BP (ca. 1930-1530 cal. BC). While climatic factors may have played a major role in its delayed installa- tion, these new pollen analyses provide the firstpollen evidence of an anthropogenic factor particularly for the late Neolithic – early Bronze Age transition when increased human pressure (woodland clearances and presence of agricultural and grazing indicators) is evidenced. Different stages related to human activities are shown for the following periods. According to the pollen data, between ca. 2350-2100 cal. BP (ca. 400-150 cal. BC), the second Iron Age, and more particularly, the 4th-2nd centuries BC, represents an important threshold in the shaping of this medium mountain cultural landscape. Large beech-oak forest clearances are related to an important agropastoral extension which continues to increase during the beginning of the Roman period. Key-words: vegetation history, Holocene, pollen, human impact, palaeoenvironment, Massif Central RÉSUMÉ DYNAMIQUE HOLOCÈNE DE LA VÉGÉTATION ET ÉVOLUTION DE L’IMPACT ANTHROPIQUE DE LA PRÉHISTOIRE À L’ÉPOQUE ROMAINE SUR LE PLATEAU DE MILLEVACHES (LIMOUSIN, MASSIF CENTRAL, FRANCE) : NOUVELLES CONTRIBUTIONS PALYNOLOGIQUES Quatre nouvelles analyses polliniques concernant différentes zones humides du plateau de Millevaches (Limousin, Massif central, France), comparées à une séquence située dans le nord du Limousin (Monts d’Ambazac) et étayées par onze datations radiocarbones AMS ont été menées de façon à reconstituer la dynamique holocène de la végétation et pour reconstruire, pour la première fois, l’évolution des impacts anthropiques sur l’environnement végétal. L’histoire de la végétation du plateau de Millevaches présente de nombreuses singularités individualisant nettement ce secteur du coeur du Massif central. Les démarrages de Corylus et de Quercus sont simultanés et datés de ca. 10560-10150 cal. BP (ca. 8550-8200 cal. BC). La composition du couvert arboréen, dominé par Corylus, demeure stable jusque vers ca. 8050-7650 cal. BP (ca. 6100-5700 cal. BC) où le recul de cette essence s’accompagne d’une expansion régionale de Quercus. Les chênaies diversifiées s’étendent rapidement avec notamment un développement conséquent de Tilia tandis qu’une première trace d’anthropisation est révélée par les indices polliniques au Néolithique ancien, autour de 6600-6500 cal. BP (ca. 4600-4500 cal. BC). L’arrivée de Fagus se fait autour de 5660-5300 cal. BP (ca. 3700-3400 cal. BC) ce qui constitue un retard de près de 700 ans par rapport à la proche Haute-Auvergne. Les premières chênaies-hêtraies sont postérieures à ca. 4800- 4400 cal. BP (ca. 2850-2450 cal. BC) et ce n’est que postérieurement à ca. 3900-3550 cal. BP (ca. 1930-1530 cal. BC) que Fagus constitue l’essence dominante. Si un forçage climatique à cette installation différée a toujours été avancé par le passé, ces nouvelles analyses polliniques apportent les premiers témoignages à une possible contribution anthropique particulièrement pour la transition Néolithique final/Bronze ancien où une hausse sensible de la pression anthropique est attestée. D’après les données polliniques, entre ca. 2350-2100 cal. BP (ca. 400-150 cal. BC), le second Âge du Fer, et plus particulièrement les 4e-2e siècles BC, constitue un seuil dans la configuration de ce paysage culturel de moyenne montagne. En effet, d’importantes déforestations des hêtraies-chênaies sont accompagnées d’une emprise agropastorale qui continue de croître au début de la période romaine. Mots-clés : histoire de la végétation, Holocène, pollen, anthropisation, paléoenvironnement, Massif central 1 Clermont Université, Université Blaise Pascal, GEOLAB, Maison des Sciences de l’Homme, BP 10448, F-63000 Clermont-Ferrand. 2 UMR 6042 CNRS (GEOLAB), Laboratoire de Géographique physique et environnementale, 4 rue Ledru, F-63057 Clermont-Ferrand cedex 1. Courriel : [email protected] 3 Laboratoire Chrono-environnement, UMR 6249 CNRS, Université de Franche Comté, 16 route de Gray, F-25030 BESANÇON cedex. Courriels : [email protected], [email protected] Manuscrit reçu le 25/05/2010, accepté le 19/01/2011 1103-151 Mep.indd 59 7/06/11 13:03:09 148 1 - INTRODUCTION spatio-temporal resolution preventing a detailed land-use history reconstruction. Recent archaeological and palaeoenvironmental studies This paper presents the results of the firstpollen analyses carried out in different western and central European carried out in the Limousin, and more particularly in the mountains provide a new concept of mountainous areas upper part of this area called the “plateau de Millevaches”, since they revealed significante vidence of upland human with the following overall objectives: occupation and landscape management that can be traced – to more accurately determine the regional Holocene back to the Mesolithic period (for example, in Pyrenees vegetation changes, and (Galop, 1998; Rendu, 2003; Miras et al., 2007, 2010; – to draw the firstrh ythms in the human impact history Palet et al., 2007; Ejarque et al., 2009, 2010; Mazier et from the Neolithic to the Roman period on a regional al., 2009), in Jura (Gauthier, 2004; Richard & Ruffaldi, scale. 2005), and in Alps (Oeggl & Wahlmüller, 1993; Moe The pollen data presented come from four peat sequences & Hjelle, 1999; Walsh & Richer, 2006; Court-Picon, – one of them studied at a high temporal resolution – 2007)). However, such interdisciplinary studies are still situated in the “plateau de Millevaches” (French Massif scarce in the whole French Massif Central (Miras et al., Central). They are also compared with one peat sequence 2003, 2004a; Argant & Cubizolle, 2005; Stebich et al., situated at a lower altitude in the northern Limousin 2005; Prat, 2006; Pulido Avil, 2006; Jouffroy-Bapicot uplands called “Monts d’Ambazac” (fig. 1 and tab. 1). et al., 2007; Trément et al., 2007; Surmely et al., 2009) and do not concern the Limousin area located in the north-western part of the French Massif Central at all. Moreover, despite two isolated case studies (Diot in 2 - STUDY AREA Allée et al., 1997; Valadas & Marambat, 1999), previous pollen analyses carried out in the Limousin were focused The “plateau de Millevaches” (pdM) is a granite on Holocene vegetation history (Denèfle et al., 1980; plateau (150 km long and 40 km wide) located in the Guenet, 1993) and provided pollen diagrams with a low north-west of the French Massif Central. Ranging 800 600 400 m Fig. 1: Location of the studied peat sequences. Fig. 1 : Situation des séquences tourbeuses étudiées. 1 Dauges (46°00’45”N, 1°25’00”E, 550 m a.s.l.) - 2 Longeyroux (45°35’40”N, 2°46’40”E, 800 m a.s.l. ) - 3 Ribière nègre (45°43’21”N, 2°28’40”E, 750 m a.s.l. ) - 4 Chabannes (45°38’57”N, 2°18’38”E, 800 m a.s.l.) - 5 Malsagne (45°43’55”N, 2°26’20”E, 800 m a.s.l.) 1103-151 Mep.indd 60 9/06/11 9:20:37 149 Description Sites Location Corings Latitude Longitude Altitude Samples (m a.s.l.) intervals Very large Longeyroux Plateau de Millevaches – Corrèze Longeyroux – 2 45°36’01"N 2°05’02"E 800 1 cm basin (Meymac, Chavanac, St-Sulpice, St-Merd) (center of the (surface area peat bog) of 1000 ha) Ribière Plateau de Millevaches – Corrèze 45°42’00"N 2°2’38"E 750 10 cm nègre (Peyrelevade) Malsagne Plateau de Millevaches – Corrèze coring in the 45°43’55"N 2°02’18-1"E 800 5 and 10 cm (Peyrelevade) deepest area large basin Chabannes Plateau de Millevaches – Corrèze 45°38’57"N 2°00’03"E 800 5 cm (surface area (Tarnac) of 50 ha) Dauges Monts d’Ambazac – Haute-Vienne 46°00’45"N 1°25’00"E 550 10 cm (Saint-Léger-la-Montagne) Tab. 1: Description and geographical data of the studied peat sequences. Tab 1 : Description et coordonnées géographiques des séquences tourbeuses étudiées. in altitude from 700 to 900 m a.s.l., it is the highest 4 - RESULTS AND INTERPRETATIONS part of the “Montagne Limousine”. This region is characterized by an oceanic-montane climate. The mean 4.1 - DATING annual temperature is about 7.5°C and the mean annual rainfall varies from 1600 to 1700 mm (Valadas & Allée, Radiocarbon dates are shown in table 2.