Striking forest revival at the end of the Roman Period in north-western Europe

Palynological analyses from a macro-estuarine sedimentary environment in north-western France over the last 2500 years BP reveal an atypical, 300-year-long increase in arboreal pollen between 1700 and 1400 years BP (ca. AD 250–550), termed the 1.7–1.4 ka Arboreal Pollen (AP) event. Tree pollen percentages exceeded both modern and Mesolithic values. This climatic interval coincides with evidence of coastal societal withdrawal in Brittany in an unfavorable socio-economic context. The study suggests that strengthening of the subpolar North Atlantic gyre (SPG) and increased recurrence of storminess extremes influenced coastal socio-environmental trajectories, contributing to a local collapse of coastal agrarian societies partly forced by climatic degradation at the end of the Roman Period.