Multiple Stable States

Human activity has the potential to collapse vegetation at the biome scale from one stable state to another, but well-documented instances of changes in biome stability are scarce. Demonstrating such a collapse requires evidence that vegetation had alternative states before an intensification of human activity, and that it subsequently stabilized to a single state. We reconstructed a biome-scale state shift across the U.S. upper Midwest based on historical (mid-1800’s) and contemporary (1999 - 2016) vegetation survey data. Before extensive fire suppression, logging, and land use conversion, vegetation structure and composition were bimodal with respect to the environment, but now consist of a single stable forested state that would have been unstable in the historical period. This collapse of historical vegetation carries cautionary parallels to modern multiple-stable-state systems facing anthropogenic changes.