Laurent Lespez

Geomorphic responses to long-term land use changes in Eastern Macedonia (Greece)

Distinct phases of stream aggradation, soil erosion and landscape stability in the basin of Drama (Eastern Macedonia, Greece) over the past 7000 years can be tied directly to long-term land use changes. During the Middle and Late Holocene, 1–4 m of alluvial fill accumulated in the centre of the basin and along the Angithis valley. Low levels of alluvial aggradation were recorded during the Late Neolithic and the Early Bronze Age (7400–4000 cal. BP). In the centre of the basin, along the lower course of the River Xeropotamos, the rate of aggradation has doubled since the Late Bronze Age (0.5–0.6 mm year−1) compared to the Holocene as a whole (0.25 mm year−1). Moderate rates of alluvial fill were experienced during the Late Bronze Age (3600–3000 cal. BP), but the most significant destabilisation of the soils occurred later than in many regions of Greece. Two historical phases of alluvial aggradation and soil erosion are identified, in the Antique and the Early Byzantine Era (3rd century BC–7th century AD) and more significantly in the Ottoman period (beginning of the 15th to the 20th century AD). In the latter period, the rate of accumulation was three to five times greater than in the Late Holocene. Almost three millennia intervened between the arrival of the first farmers and the onset of erosion. This is mainly explained by the settlement pattern during the Neolithic and the Early Bronze Age. It seems that the early farmers preferred to cultivate the more stable soils on the gentle slopes at the centre of the basin. During the Late Bronze Age, the land use pattern changed. The soils then under cultivation on the foothills were less stable and the steeper slopes were more susceptible to erosion. This limited the potential for forest restoration after the first noticeable land clearance, and probably explains the extent of alluvial aggradation. Since the Antique Era, the intensity of land use has increased. The two phases of accelerated alluviation in historical times are clearly linked to land use changes, particularly with the upstream progression of cropping and grazing onto more sensitive lands in foothills and mountainous areas, though this was also influenced by climatic fluctuations. The major period of aggradation in the Ottoman period is clearly associated with both climatic and anthropogenic factors. It seems that the early historic deforestation and agricultural activities rendered river systems more sensitive to relatively modest changes in climate.

The emergence of pottery in Africa during the tenth millennium cal BC: new evidence from Ounjougou (Mali)

New excavations in ravines at Ounjougou in Mali have brought to light a lithic and ceramic assemblage that dates from before 9400 cal BC. The authors show that this first use of pottery coincides with a warm wet period in the Sahara. As in East Asia, where very early ceramics are also known, the pottery and small bifacial arrowheads were the components of a new subsistence strategy exploiting an ecology associated with abundant wild grasses. In Africa, however, the seeds were probably boiled (then as now) rather than made into bread.

Phytolith taphonomy in the middle- to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)

In semi-arid ecosystems where lacustrine sediments are rare, bio-proxies preserved in fluvial deposits are needed to understand environmental changes. In this study, we evaluate the potential of phytoliths as a bio-proxy in the Yamé River’s deposits at Ounjougou (Mali, West Africa) covering the middle to late Holocene (7790–4000 cal. BP). In soils, phytolith assemblages result mainly from decomposition of local vegetation but in alluvial deposits, the taphonomy of phytoliths is more complex, depending on the type of transport and deposition. In order to define the spatial origin of the phytolith assemblages, either from local (valley floor) or regional vegetation (catchment area), we took the sedimentary characteristics of the deposits into account. Using a combination of general and index approaches, phytoliths of 14 modern and 29 fossil samples from the Yamé valley were analyzed. The predominant source area of represented phytoliths varies with the fluvial energy of transport. Channel deposits, carried during periods of strong fluvial activity, contain higher numbers of savanna grass phytoliths and display a lower ratio of dicotyledon versus Poaceae phytoliths (D/P) than those deposited in the floodplain where phytoliths from the local gallery forest are more strongly represented. From the 5th millennium BP onwards, higher percentages of grass short cell phytoliths (GSCP) and lower D/P values point to gradual vegetation opening due to increasing aridity. High amounts of burned phytoliths show regular fire incidence in the gallery forest and attest for human impact on the landscapes of Ounjougou from the 7th millennium BP onwards. After 4500 cal. BP, there is evidence for pearl millet cultivation.

The lowest levels at Dikili Tash, northern Greece: a missing link in the Early Neolithic of Europe

Tells famously capture the historical sequences of the earliest farmers—but digging them is not easy. With a depth of strata of 17m at Dikili Tash, the earliest occupation was out of reach of a trench. But our researchers got there by coring, extending the date of the first occupation back 1000 years, and deducing, from small samples, the changing environment and possible connections with Anatolia.

Towards a Better Understanding of Sub-Saharan Settlement Mounds before AD 1400: The Tells of Sadia on the Seno Plain (Dogon Country, Mali)

Dans la boucle du Niger, plusieurs etudes ont montre l’existence de buttes anthropiques qui se sont developpees principalement entre le premier millenaire avant J.-C. et le 15eme siecle de notre ere. Bien que les connaissances sur les tells subsahariens aient recemment ete enrichies, de nombreuses questions restent a elucider. En effet, les don- nees chronostratigraphiques precises disponibles restent rares par rapport a la zone geographique et a la periode impliquees. Ce relatif manque de longues sequences limite fortement l’integration diachronique de donnees culturelles, economiques et environnementales, necessaire a la compre- hension des mecanismes sous-jacents a l’emergence et au developpement de ce type de sites. Dans cet article, nous presentons les resultats obtenus lors des fouilles que nous avons recemment menees sur un ensemble de buttes anthro- piques a Sadia, dans la plaine du Seno (Pays Dogon, Mali), qui ont permis de definir une sequence chronologique, culturelle et environnementale precise. L’integration de ce travail et des resultats d’une approche extensive menee dans l’ensemble du Pays Dogon depuis plus de 15 ans nous permet de proposer un scenario de l’occupation des tells du Seno, ainsi qu’une reflexion sur le developpement des societes rurales saheliennes et leurs interactions avec les premiers Etats de la boucle du Niger, avant 1400 AD.

The relationship between vegetation and modern pollen assemblages on Mount Paggeo (NE Greece)

In this study, we investigated the relationship between vegetation and modern-pollen rain along the elevational gradient of Mount Paggeo. We apply multivariate data analysis to assess the relationship between vegetation and modern-pollen rain and quantify the representativeness of forest zones. This study represents the first statistical analysis of pollen-vegetation relationship along an elevational gradient in Greece. Hence, this paper improves confidence in interpretation of palynological records from north-eastern Greece and may refine past climate reconstructions for a more accurate comparison of data and modelling. Numerical classification and ordination were performed on pollen data to assess differences among plant communities that beech ( Fagus sylvatica ) dominates or co-dominates. The results show a strong relationship between altitude, arboreal cover, human impact and variations in pollen and nonpollen palynomorph taxa percentages.

Analyse spatiotemporelle de la dynamique fluviale d’un cours d’eau sahélo-soudanien entre 1967 et 2007. Le cas du Yamé au pays Dogon (Mali, Afrique de l’Ouest)

En Afrique de l’Ouest, les etudes menees sur les systemes fluviaux sont rares et ont principalement ete conduites a petite echelle en integrant le role du climat comme le seul facteur intervenant dans la dynamique de ces milieux. Les travaux presentes ici concernent la dynamique fluviale recente d’un petit bassin versant de 4400 km², celui du Yame (pays Dogon, Mali). Nous proposons une methode d’analyse semi-automatique diachronique permettant de caracteriser le fonctionnement actuel et de quantifier les ajustements morphologiques du systeme fluvial entre 1967 et 2007 ; periode qui fut entrecoupee d’annees de secheresse au Sahel. Elle s’appuie sur la definition d’une typologie morphologique des differents styles fluviaux contemporains et ablie a partir d’un decoupage en troncons homogenes et du calcul de variables et d’indices. Cette etude revele, (1) pour la periode actuelle, une diversite longitudinale du systeme fluvial et (2) pour les dernieres decennies, une reponse heterogene du bassin versant suite a une modification des variables de controle d’origine climatique (secheresse) et anthropique (pression demographique...).