Wetland restoration: The potential for assembly rules in the service of conservation

One of the pressing problems for applied ecologists is the efficient restoration of structure and function to degraded ecosystems. Where some other conservation activities, such as protection of existing wilderness, continue to require making the best of increasingly bad situations, the goal of restoration raises the pleasing prospect of measurable improvement in landscapes. Restoration simultaneously provides the ultimate test for the discipline of community ecology: ecologists should be able to build an ecosystem in the same way an engineer builds a bridge, with a list of parts connected in specified ways leading to certain reliable outcomes. Failures would reveal that scientists do not adequately understand the system. Practical considerations suggest the application of tools that already exist rather than the invention of new ones. The objective of this paper is to suggest that two valuable tools may already exist, tools that provide an intellectual foundation for restoration ecology. Such a foundation is necessary because there has been a tendency for restoration ecology to represent a haphazard collection of individual cases rather than a well-defined discipline with repeatable methods. One possible scheme for unifying studies of restoration is that provided by assembly rules, where predictions are based upon key environmental factors and the responses of species to those factors. The potential of such assembly rules is introduced using three examples: fish in wetlands, plants in salt marshes, and plants in prairie potholes. I then describe an experiment where a standard species pool of wetland plants was sown into twenty-four different sets of environmental conditions, illustrating how landscapes can select communities out of larger pools. A second possible tool is indicators of ecosystem integrity. These can measure whether a project actually works. Clear discrimination between success and failure can improve restoration procedures by accelerating the evolution of management principles and techniques; Holling has called this process 'adaptive environmental assessment.' I conclude with the optimistic view that restoration already has the tools for continued progress; what is needed is primarily their intelligent application. That is, rather than ending with a typically academic plea for more research, I suggest (for a change) char what is needed is only the discriminating application of procedures and principles that already exist.