Distinguishing prehistoric human influence on late-Holocene forests in southern Ontario, Canada

Abstract

The influence of Native Americans on late-Holocene forests of North America remains a contentious issue, as it is unclear whether vegetation transitions inferred from pollen records are a product of prehistoric human disturbance. In southern Ontario, the adoption of maize agriculture coincides with neoglacial cooling, so distinguishing the relative roles of prehistoric people and climatic change in shaping forest composition requires that pollen records be interpreted in a regional context. In this study, we objectively identify pollen records from the southern Ontario region which exhibit periods of significant pre-European anthropogenic disturbance in the context of the archeological record. This enables a comparison of pollen records shaped primarily by climatic cooling with those disturbed by prehistoric human forest clearance. Our results suggest that regional-scale late-Holocene cooling resulted in a gradual and synchronous shift from deciduous to boreal taxa. However, forest clearance by Native Americans resulted in a secondary succession characterized by the replacement of late-successional beech-maple forest with ruderal species, grasses and poplar, followed by mid-successional oak and white pine. This transition consistently coincides in space and time with an increase in archeological records of human occupation. The method we have developed here to distinguish significant prehistoric human impacts could be applied to pollen records in other regions, or on a continental scale.