Fabaceae (legume) pollen as an anthropogenic indicator in eastern North America

Abstract

European land-use indicators in North America typically include pollen from Poaceae (grasses), Ambrosia (ragweed), Rumex (dock), and/or Plantago (plantain). A potential complement to this list is Fabaceae (legumes), members of which were introduced by colonists to eastern North America. Historical records show that Trifolium (clover) was widespread from the earliest days of colonization, and several other Eurasian legumes were also introduced for livestock forage by 1840 ce. As an insect-pollinated family with taxa native to the region, Fabaceae is not usually emphasized in palynological reconstructions. However, Plantago is commonly used as an indicator despite being represented by native and insect-pollinated varieties. Likewise, it can be difficult to distinguish between native and introduced Poaceae, yet an increase in grass pollen is generally taken as a disturbance indicator. In order to assess the value of Fabaceae as an indicator of the settlement horizon, the R package neotoma was used to retrieve Fabaceae pollen data from the Neotoma Paleoecology Database to assess regional trends in abundance and for comparison to the usual suite of taxa. Results confirm the possible utility of Fabaceae as an anthropogenic marker in the study area. Two case studies with good chronological control illustrate how all five taxa can be found at the settlement horizon across the study area and over time: a 14C and 210Pb-dated pond in Connecticut anthropogenically impacted by 1700 ce, and a varved lake in Ontario impacted by 1840 ce.