The Dynamic Reference Concept: Measuring Restoration Success in a Rapidly Changing No-Analogue Future

The “past as prologue” approach to ecological restoration is increasingly problematic due to global climate change, invasive species, and human perturbations that are outside of evolutionary boundaries, all of which argue for new conceptual approaches to restoration. We present the dynamic reference concept, an approach that quantitatively incorporates the temporal and spatial variation of reference ecosystems such that targets reflect ecological dynamism. Success is measured by simultaneously quantifying changes in reference and restoration sites over time. To illustrate the practical application of this concept, we present a case study of longleaf pine (Pinus palustris) restoration on Eglin Air Force Base, Florida, USA. We use Mahalanobis distance with non-metric multidimensional scaling ordination to quantify the dynamic nature of reference plots and the extent to which restoration sites move toward them. Reference ecosystems were first defined by expert judgment and ecological models including maximum entropy. We then further refined restoration targets through data analysis using Mahalanobis distance to determine plots that were within the 90% confidence region of initial benchmark species composition. Species composition of benchmark sites was more resilient than restoration sites, i.e., changing less with a natural disturbance regime of frequent fire. Restoration sites with higher fire frequency moved more rapidly towards the reference conditions than sites with fewer fires. By quantifying the “moving target” of reference ecosystems while simultaneously measuring change of restoration sites, this application of the dynamic reference concept offers promise to manage for reference conditions that are achievable in a world where change is the norm.