Resistance and Resilience to Natural Disturbance during Ecological Restoration

An uncertainty in ecological restoration is how natural disturbances occurring during restoration might influence restoration outcomes. The unplanned nature of natural disturbances makes them difficult to study, and their effects hinge on the resistance or resilience of ecosystem components that may change during restoration. In 2010, a tornado struck a 23-year-old oak woodland-savanna restoration site in northwestern Ohio, USA, providing a rare opportunity to determine how a major natural disturbance could influence the course of restoration. Restoration burning had begun at the site in 1988. We monitored tree and understory metrics before restoration, in 10 of the 22 years during restoration before the tornado, and in two of five years after the tornado until 2015. Trajectories in floristic quality and conservation-priority plant species (e.g., state-listed rare species) were resistant to change by the tornado, non-native plants were resilient (which was desirable as they quickly declined to near pre-tornado levels after an initial increase), and the oak overstory was neither resistant nor resilient. Overstory density was halved after the tornado, moved from woodland toward savanna, and then changed little. Forbs and oaks in the understory were the main increasers after the tornado. The tornado disturbance altered the pathway of restoration but remained consistent with restoration goals, given that both woodlands and savannas were part of reference conditions and conservation-priority forbs increased.