Climatic and Societal Causes for Abrupt Environmental Change in the Mediterranean During the Common Era

We compare climatic and societal causes for abrupt environmental change for the last 2000 years in the Rieti Basin, central Italy using high-resolution sedimentary paleoenvironmental proxies, historical documents, and annually resolved independent climate reconstructions of temperature and precipitation. Pollen zones, identified from temporally constrained cluster analysis, coincide with historic periods developed from well-established ceramic sequences corresponding to the Roman Imperial through Late Antique (1 to 600 CE) Early Medieval (600 to 875 CE), Medieval through Late Medieval (875 to 1400 CE), Renaissance and Modern (1400 to 1725 CE), and Contemporary periods (1725 CE to present). Non-metric dimensional scaling (NMDS) ordination showed that each temporal period occupied a unique ecologic space suggesting that a new landscape was created during each successive historic period. During Roman time, between 1 and 500 CE, a modest decline in forest coincides with a positive phase of the North Atlantic Oscillation (NAO) and drier climate; however mesophyllous forest is preserved. Steep decline in forest cover between 850 and 950 CE coincides with positive temperature anomalies in Europe and a positive NAO. Although this would seem to suggest climate as a cause, temperature and precipitation changes are modest and the magnitude and rapidity of the vegetation change suggests climate played a small role. Archaeological evidence from across Europe identifies socioeconomic factors that produced forest clearing. In contrast, cooler temperatures and a negative NAO (increased ppt) appears to have been a catalyst for land abandonment and forest recovery in the 13th to 14th centuries. The NAO produces opposite effects on societies in the eastern and western Mediterranean with the negative phase in 1400 CE leading to cool wet climate and land abandonment in central Italy but an abrupt shift to drier conditions and change from sedentary village life to nomadism in Syria.