Late Holocene vegetation changes in relation with climate fluctuations and human activity in Languedoc (southern France)

Abstract

Abstract. Holocene climate fluctuations and human activity since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean paleoenvironmental changes over the last millennia remains a challenging issue. High-resolution pollen analyses were undertaken on two cores from the Palavasian lagoon system (Hérault, southern France). These records allow reconstruction of vegetation dynamics over the last 4500 years. Results are compared with climatic, historical and archeological archives. A long-term aridification trend is highlighted during the late Holocene, and three superimposed arid events are recorded at 4600-4300, 2800-2400 and 1300-1100 cal BP. These periods of high-frequency climate variability coincide in time with the rapid climatic events observed in the Atlantic Ocean (Bond et al., 2001). From the Bronze Age (4000 cal BP) to the end of the Iron Age (around 2000 cal BP), the spread of sclerophyllous taxa and loss of forest cover result from anthropogenic impact. Classical Antiquity is characterized by a major reforestation event related to the concentration of rural activity and populations in coastal plains leading to forest recovery in the mountains. A major regional deforestation occurred at the beginning of the High Middle Ages. Around 1000 cal BP, forest cover is minimal while the cover of olive, chestnut and walnut expands in relation to increasing human influence. The present-day vegetation dominated by Mediterranean shrubland and pines has been in existence since the beginning of the 20th century.

Influence of the North Atlantic subpolar gyre circulation on the 4.2 ka BP event

“…Both cores were collected as part of the international IMAGES program (International Marine Past Global Change Study). The third core KSGC-31 (43 • N, 3.29 • E; 60 m water depth) was recovered from the Gulf of Lion inner-shelf mud belt during the GM02 Carnac cruise in 2002 (Bassetti et al, 2016). The age model of this core is based on 17 14 C dates measured on bivalve shells (Table S1, Fig.…”

The Holocene history of low altitude Mediterranean Fagus sylvatica forests in southern France

“…This study presents a high-resolution pollen sequence from the Palavas coastal lagoon (Figure 1a) covering the last 7,800 years, an extension of a previous study published by Azuara et al (2015) focusing on the last 4,500 years. Here, we aim to investigate the past dynamics of Holocene Mediterranean beech forests by comparing the new pollen record to published charcoal data from the Languedoc and the lower Rhône Valley, and further pollen data from southeast France.…”

“…The long-term decrease in Fagus proportions within coastal sequences at around 3,000 years cal BP coincides with decreasing arboreal pollen proportions and increasing evergreen Quercus (Figure 2; Sanchez-Goñi, 1995;Jalut et al, 2009). This progressive deforestation, evident since 3,000 years cal BP, suggests that human activities, together with long-term aridification, could have contributed to the long-term decrease of beech forests in the Languedoc (Azuara et al, 2015), especially after 1,500 years cal BP when Mediterranean shrubs and cultivated taxa rise significantly ( Figure 2). Human pressure during the Early Medieval Period (~1,500 years cal BP) was certainly much higher than during the late Neolithic period (5,250 years cal BP).…”

Reply to Anonymous Referee #2

“…(1) Marine core MD95-2015 (this study); (2) marine core MD99-2275 (this study); (3) marine core GS06-144 08GC (Mjell et al, 2015); (4) marine core RAPiD-12-1K (Thornalley et al, 2009); (5) marine core P-013 (Solignac et al, 2004); (6) marine core JM96 1207 (Solignac et al, 2006); (7) ice core GISP2 (O'Brien et al, 1995); (8) marine core Fox05R/04G (Andresen et al, 2012); (9) marine core MD95-2011 (Berner et al, 2011); (10) marine core KSGC-31 ; (11) core PB06 from the Palavasian Lagoon (Azuara et al, 2015); (12) speleothem from Renella Cave (Zanchetta et al, 2016); (13) speleothem from Gueldaman Cave (Ruan et al, 2016). Subpolar and subtropical gyres as well as main surface currents in the North Atlantic are also shown.…”