Environnement végétal et collecte du bois de feu au Néolithique dans le sud du bassin de l'Escaut (5 200-2 200 BC)

EnglishThis comparison of palynological (73 spectra) and anthracological (9 sites, 305 samples) results aims to understand the environment in which the sites are located and the vegetation dynamics during the Neolithic period in the southern Scheldt basin (5 200-2 200 BC). The seven regional palynological sequences cover the first part of the Atlantic to the Subboreal chronozone (i.e. 6 500 to 1 000 BC). The palynological spectra are distributed over seven sequences that come mainly from valley bottoms, near or at some distance from Neolithic sites. Others come from riverbank dated by archaeological material and radiocarbon dates. A sequence comes from a stratified archaeological structure whose primary use is interpreted as a flax retting pit. Regarding charcoal analysis, the Early Neolithic period is represented by one Linearbandkeramik site that includes two phases of occupation. The four sites from the Middle Neolithic II period (4 200-3 800 BC) belong to the Spiere group. The Final Neolithic period (2 900-2 200 BC) is constitute of four sites attributed to the Deule-Escaut group. Two types of sites are distinguished. Aubechies, Sauchy-Lestree, Marquion and Rebreuve-Ranchicourt are habitat sites without palisades or enclosures, located on well-drained soils. The ditches and/or fencing enclosures of Spiere, Carvin, and the two sites of Houplin-Ancoisne are located on wet soils, with or without preserved houses. The charcoal fragments come from detrital fillings of hollow structures (pit, posthole, ditch segment) or riverbank deposits. In these contexts, charcoals are generally diffuse in the sediment and may correspond to firewood, that is to say wood harvested in the first instance for combustion activities. Nevertheless, the anthropic activities at the origin of charcoal deposits can be heterogeneous. Some of the charcoal fragments could correspond to by-products of timber processing used, in a second stage, as firewood. Two methods of counting are applied to observe the relative importance of each taxon during the Neolithic period. First, the fragments are counted for each identified taxa. It is the classical method applied in anthracology. Secondly, the number of occurrences is calculated in each assemblage for each taxa (i.e. each taxa determined in a given sample is counted as a single individual). This is equivalent to calculate the minimum number of logs set on fire for each taxa on the Neolithic site. It offsets the risk of over-representation of some taxa that are regularly presents but with a small charcoal quantity. Over 300 samples and 7 000 fragments are taking into account. Beyond 700 fragments identified at the site scale, the taxonomic list does not increase. The number of taxa seems to be more influenced by the number of samples studied. From a methodological point of view, this means that the multiplication of sampling on the field (in at least 15 contemporary structures) makes it possible to obtain an anthracological assemblage representative of the diversity of the forest formations travelled for firewood. Furthermore, the rank of taxa calculating according to the two methods is generally coherent. The importance of oak is somewhat reduced with the occurrence calculation. Seventeen wood taxa are recorded and could correspond to three forestry groups. The oak forest is constitute of a more or less diversified undergrowth including hazelnut. It develops on stations with moderate to no drainage, and is supplement with ash on wet stations. Forest edges characterized by the importance of Rosaceae (Maloideae and Prunoideae) accompanied by a procession of shrub species that appreciate light and tolerate semi-shade. Currently, secondary groves with Maloideae appear after abandoning agricultural activities, forest clearing or are the result of anthropogenic disturbances. The alder forest is also visible thanks to the alder tree, which is the main representative in its mature state. It grows in alluvial forests whose soils are waterlogged all year round. The poplar-willow is, with the birch, characteristic of the pioneering stage of the development of the riverside vegetation. Palynological synthesis indicates that the first Neolithic groups of the southern Scheldt basin arrived in a forested environment where lime (Tilia sp.), hazelnut (Corylus avellana) and oak (Quercus sp.) are predominant. The importance of hazelnut in the Early Neolithic (5 200-5 000 BC), at the sources of the Dendre river, may be linked to a delay in the recovery of the locally deciduous oak forest, but also to previous Mesolithic human practices that could have favored the development of the tree. Lime dominates the majority of palynological sequences in the Atlantic chronozone. The taxon is therefore under-represented in firewood resources compared to its availability near Neolithic sites. The species has a soft wood resulting to small and light charcoal fragments. Moreover, lime is used to make textile, like rope, during the Neolithic, that could therefore imply a preservation of lime stands, and result in the low representation of the taxa in the charcoal assemblages. During the second half of the Atlantic, the woody environment changes little, except for the alder (Alnus sp.) forest, which develops at the bottom of the valley. The Spiere communities (4 200-3 800 BC) travelled through diverse environments for fuel gathering. Oak is generally widely dominant, raising the question of its over-representation in anthracology to the detriment of lime and hazelnut, which are still clearly visible in palynology. Oak could correspond to by-product of timber reused in a second phase for fuel. The use of oak for timber is attested on several sites of south Scheldt basin. Anthracology also well record the riverside vegetation, at different stages of its development depending of the site. The mature alder forest is mainly visible on sites with enclosures whereas the pioneer riparian forest is recorded on habitat sites. The gathering of forest edges, with Maloideae, is particularly marked during the Middle Neolithic II. In the Subboreal, the increased atmospheric humidity is noted with the arrival of beech (Fagus sp.) in palynology and yew (Taxus baccata) in anthracology. The Deule-Escaut groups (2 900-2 200 BC) collected their fuel from oak-ash forests. Edges on dry soils are more visible on habitat sites and mature alder forests on enclosure sites. For example, alder signal is decreasing on a palynological sequence near a final Neolithic enclosed site where alder charcoal fragments are particularly numerous. The importance of the riverside vegetation and ash can thus be correlated with the location of sites along the riverbank, but perhaps also with the setting up of wetlands for human installation. In addition to yew, maple is also characteristic of the Deule-Escaut period. francaisCette comparaison des resultats palynologiques (73 spectres) et anthracologiques (9 sites, 305 prelevements) a pour but d’apprehender l’environnement dans lequel les sites sont implantes et la dynamique de la vegetation au cours du Neolithique dans le sud du bassin de l’Escaut. Les premiers groupes neolithiques sont arrives dans un milieu ou predominent le tilleul, le noisetier et le chene. Dans les assemblages anthracologiques du Rubane (5 200-5 000 BC), la domination du noisetier pourrait etre liee a un retard dans la reconquete de la chenaie aux sources de la Dendre, mais aussi a des pratiques humaines mesolithiques anterieures. Le tilleul est sous-represente dans les ressources en bois de feu par rapport a sa disponibilite pres des sites neolithiques. Durant la seconde moitie de l’Atlantique, l’environnement ligneux evolue peu, sauf l’aulnaie qui se developpe en fond de vallee. Les communautes du groupe de Spiere (4 200-3 800 BC) ont parcouru des milieux diversifies pour la collecte du combustible. Le chene est generalement largement dominant posant la question de sa surrepresentation en anthracologie au detriment du tilleul et du noisetier encore bien visibles en palynologie. La ripisylve est bien enregistree par l’anthracologie, a different stade de son developpement. L’aulnaie mature n’est visible que sur les sites a enceinte et la collecte des lisieres a Maloideae sont particulierement marquees a cette periode. Au Subboreal, on assiste a une augmentation de l’humidite atmospherique avec l’arrivee du hetre (en palynologie) et de l’if (en anthracologie). Les groupes du Deule-Escaut (2 900-2 200 BC) ont collecte leur combustible au sein de la chenaie-frenaie et, selon les sites, les lisieres sur sols sec (sites d’habitat) ou l’aulnaie mature (sites a enceinte). L’importance de la ripisylve et du frene peut etre correlee a la localisation des sites en bordure de berge, mais peut-etre aussi, par les modalites d’amenagement de ces zones humides. En plus de l’if, l’erable est egalement caracteristique de la periode.