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

Abstract

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.