Using natural disturbance and portfolio concepts to guide aquatic-riparian ecosystem management
The U.S. Forest Service and other federal land managers are responsible for maintaining the productivity of aquatic–riparian ecosystems, the associated native biota, and the ecosystem services they provide. These public lands are important sources of water, recreation opportunities, and habitat for a suite of animals and plants, including many that are protected under the Endangered Species Act. To meet these challenges and responsibilities, recent science suggests modifying practices to provide a broader array of habitat, biological conditions, and ecosystem functions than are associated with traditional management approaches. We suggest that by linking approaches based on natural disturbance and portfolio concepts, managers can achieve a robust strategy and desired outcomes more reliably and cost effectively. Locally complex habitat conditions created by natural disturbances provide the template for biological diversity to play out provided enough time. Accordingly, natural disturbance regimes play an important role in creating and sustaining habitat and biological complexities on the landscape, and management actions can emulate natural disturbance processes at appropriate spatial and temporal scales where possible. The portfolio effect (i.e., diversity that mitigates risk) provides justification for promoting connected heterogeneous habitats that reduce the risk of synchronous large–scale population and ecosystem collapse. In this paper, we describe how disturbance and portfolio concepts fit into a broader strategy of conserving ecosystem integrity and dynamism, and provide examples of how these concepts can be used to address a wide range of management concerns. Ultimately, the outcome for populations, habitats, and landscapes depends on how well environmental change is understood, the degree to which change is appropriately addressed by natural resource managers, and on solutions that allow populations and ecosystems to persist in the presence of and be resilient to a growing scope of human influences.