Cultural innovation can increase and maintain biodiversity: A case study from medieval Europe.

Numerous research efforts have used paleoecological data to reconstruct past biodiversity in Europe. In these projects, researchers have identified increases in biodiversity over the Holocene and hinted at a positive correlation with human population. These are important findings but are not easily translated into effective biodiversity conservation and restoration policy. We argue that, in order to better inform policymaking, studies of past biodiversity dynamics should include analyses of contemporaneous cultural phenomena in order to identify and describe specific anthropogenic drivers of past biodiversity changes. We present an example here, a case study from the Lake Constance region (southwestern Germany), one of the core areas of the Carolingian Empire, the foundational political structure of modern Europe. This uniquely well-documented region offers six fossil pollen profiles characterized by high taxonomic and chronological resolution, archaeobotanical evidence from hundreds of excavation sites, and historical records describing population, commerce, and agriculture dating from the mid-700s CE. These data indicate that a major, sustained increase in plant diversity occurred in the Lake Constance region between 500 and 1000 CE, the formative period of medieval civilization. Plant diversity reached a 4,000-y peak around 1000 CE, making the medieval period a plant diversity optimum in the region. Archaeobotanical evidence independently corroborates this finding. Palynological, archaeobotanical, and archival data suggest that cultural innovations-in agriculture, management, and trade-were the primary drivers of this biodiversity transition and were necessary to maintain elevated levels of plant diversity in the region through the 20th century.