not-yet-known not-yet-known not-yet-known unknown Ecotones are expected to be sensitive to climate change, but supporting evidence is scarce. Dense paleoecological data networks are ideal for studying past ecotonal dynamics because of their broad spatiotemporal coverage. Here we test the ecotonal sensitivity hypothesis by reconstructing movements of a major temperature-governed forest ecotone over the last 11,000 years in lower Michigan and comparing the variability of ecotone-proximal and distal vegetation. NMDS ordination indicates four meaningful axes of variation in Holocene Michigan vegetation, with axis 2 capturing the latitudinal ecotone and axis 4 differentiating by moisture sensitivity. The ecotone advanced northwards by 150 km from 11 to 6 ka, during a 3.5â°CTJuly warming, then retreated. Ecotone-proximal sites have higher rates of compositional change than distal sites. These findings support the ecotonal sensitivity hypothesis, constrain estimates of climate-driven forest ecotonal movement, and reinforce concerns about the sensitivity of ecotonal ecosystems to anthropogenic global warming.
