Setting targets for severely damaged ecosystems without reference sites

Assisting the recovery of degraded ecosystems typically involves goals or targets for specific structural or functional attributes. Realistic targets, trajectories, and time frames for the restoration of those attributes are commonly developed by comparison with relatively undamaged reference sites. In much of the world, "undamaged" sites are both unavailable and unrealistic as goals. Even when adequate reference sites are available, the trajectories of recovering ecosystems can be difficult to determine with accuracy. Social, cultural, economic, and ecological realities may render historic conditions unattainable. Increasingly, our challenge is to set realistic goals, with measurable and relevant metrics, in the absence of adequate reference sites. We suggest an initial focus on repairing damaged primary processes (hydrology, nutrient cycling, and energy flows) that inhibit or prevent the natural recovery capacity of more functional systems. The most appropriate intervention strategies repair dysfunctional processes and initiate autogenic succession. The appropriate goals and metrics for highly disturbed sites are more likely to address processes like runoff rates, nutrient loss, and energy capture than structural metrics such as species diversity or composition. Knowledge of comparable systems, regional environmental conditions, soil changes, and socio-economic changes may facilitate the development of predictive models for rate changes in key processes. Trajectory analysis that assesses progress toward a realistic range of key metrics will be more effective than structurally defined assessment goals. Ultimately, our goal is to initiate positive feedback processes in the severely damaged ecosystems that continue to improve limiting rates and processes.