Historic Variability: Informing Restoration Strategies, Not Prescribing Targets

The concept of historic range of variability (HRV) is briefly evaluatedwithin the context of its application in ecosystem managementover the past two decades. Despite caveats to the contrary, animplicit assumption continues to emerge of climatic stationarity,and, by corollary, that presettlement centuries provide an appropriatereference period. This is examined from the perspective ofhistoric climate change and ecosystem response. As a means ofdeveloping reference prescriptions and management targets, HRVis generally inappropriate, although if historic periods are usedfor reconstruction that have coarse resemblance to present or projectedfuture climates, such as the Medieval Climate Anomaly ormiddle Holocene rather than the presettlement centuries, thesemight be defensible. In cases of reclamation of severely degradedecosystems, HRV prescriptions developed from analogous climateperiods could provide coarse guides. In most situations, however,historic reconstructions are best used to improve understanding ofecological response to a wide range of forcing factors, and therebyto inform (rather than prescribe) management strategies. Such historicallyinformed approaches are likely more effective than anHRV approach under future changing climate regimes for managingand restoring ecosystem function and for assisting transitionsto new ecosystem states.