Historic Variability: Informing Restoration Strategies, Not Prescribing Targets

The concept of historic range of variability (HRV) is briefly evaluated within the context of its application in ecosystem management over the past two decades. Despite caveats to the contrary, an implicit assumption continues to emerge of climatic stationarity, and, by corollary, that presettlement centuries provide an appropriate reference period. This is examined from the perspective of historic climate change and ecosystem response. As a means of developing reference prescriptions and management targets, HRV is generally inappropriate, although if historic periods are used for reconstruction that have coarse resemblance to present or projected future climates, such as the Medieval Climate Anomaly or middle Holocene rather than the presettlement centuries, these might be defensible. In cases of reclamation of severely degraded ecosystems, HRV prescriptions developed from analogous climate periods could provide coarse guides. In most situations, however, historic reconstructions are best used to improve understanding of ecological response to a wide range of forcing factors, and thereby to inform (rather than prescribe) management strategies. Such historically informed approaches are likely more effective than an HRV approach under future changing climate regimes for managing and restoring ecosystem function and for assisting transitions to new ecosystem states.