Sentinel site networks as a mechanism to evaluate progress toward meeting restoration goals in altered and unaltered landscapes

Establishing appropriate restoration targets, tracking progress toward those targets, and determining appropriate adaptive intervention are some of the greatest challenges to successful ecosystem restoration. Addressing these challenges is often informed by the use of “reference sites” that represent relatively unaltered or historical conditions and conceptually can be used to provide context and comparison for restoration projects. In reality, contemporary “unaltered” sites have often been manipulated by centuries of cultural practices and “pristine” conditions cannot be defined. Moreover, in highly altered landscapes or where stressors are continuing to rapidly reshape ecosystem structure, few or no sites may be unaltered enough to serve as pristine or aspirational reference standard sites for restoration. To address this challenge, we adapted the concept of “reference sites” to a framework for developing sentinel site networks, which consist of sites along a gradient of condition. These sites are selected for long‐term monitoring to track ecological conditions through time, to evaluate the effect of regional trends in external conditions or stressors, and to document progress toward site‐specific goals and regional objectives. Developing a sentinel site network involves screening sites based on condition, stressors, representativeness, and feasibility for long‐term monitoring, informed by input from regional experts and stakeholders. The resultant network includes sites along a gradient of condition, geographical representation, and management that can be customized or regionally based on local constraints. We demonstrate the application of this process through the development of a sentinel site network for coastal wetlands in the highly developed southern California (U.S.A.) region. This process can be readily adapted to other habitats globally and may be particularly useful in habitats that have been highly impacted by human activities.