Process-centered restoration and the concept of reference dynamics

Accurate and ecologically meaningful characterization of reference conditions is a fundamental requirement in restoration ecology. Restoration practice and research commonly define reference conditions in terms of compositional and structural elements. A wide variety of processes are central to the functioning and dynamics of ecological systems, and can be placed at the hub of restoration research and practice. We propose an alternative “process-centered” framework that can complement structural or compositional reference metrics. A process-centered approach also facilitates the definition of “reference dynamics”, where spatial and temporal variability and underlying mechanisms of change are primary. We illustrate this approach using a 303-yr reconstruction of the natural surface fire regime to guide restoration of an old-growth Pinus ponderosa forest in the Jemez Mountains of New Mexico, USA. Fire occurrence varied over space and time during the period of record, with ecologically significant variation in fire intervals (yr fire^-1) entrained by interannual variability in climate. We used forest dynamic and fire behavior models to test how modifying forest structure affected fire behavior and effects. We compared simulated results with estimates of fire behavior and effects under natural conditions, and found that the majority of change in response metrics occurred in the thinning of smaller diameter trees. A process-centered approach and the reference dynamics paradigm can replace the more static concept of “reference conditions” in defining restoration baselines and provide an improved standard of comparison for restoration ecology.