Forest re-growth on medieval farmland after the Black Death pandemic—Implications for atmospheric CO2 levels

Well-dated pollen assemblages from an organic-rich infill of an oxbow lake of the river Roer (southeastern Netherlands) provide a high-resolution reconstruction of regional vegetation development and land-use for the period between AD 1000 and 1500. Regional effects of the mid-14th century plague pandemic known as the Black Death are reflected by a period of significant agricultural regression between AD 1350 and 1440. Concomitant re-growth of forest indicates the existence of a terrestrial carbon sink following the Black Death pandemic. A direct temporal correlation of the reconstructed changes in land-cover with a proxy record of atmospheric CO2 mixing ratios based on stomatal frequency analysis of Quercus robur leaf remains suggests the coupling of long-term CO2 trends of the 13th–15th centuries and coeval trends in regional forest density. During the period of maximum reforestation between AD 1400 and 1440, CO2 levels seem to be relatively low, but the onset of a CO2 decline may predate the spread of the Black Death in Europe.