Background/Question/Methods To effectively manage natural reserves, resource managers must prepare for future contingencies while balancing the often conflicting priorities of different stakeholders. To cope with these issues, managers routinely employ models to project the response of ecosystems to different scenarios that represent alternative management plans or environmental forecasts. Scenario analysis is often used to rank such alternatives to aid the decision making process. However, model projections are subject to uncertainty in assumptions about model structure, parameter values, environmental inputs, and subcomponent interactions. In the face of ever-building environmental, social, and political, challenges, there is an urgent need for efficient strategies for dealing with these uncertainties. To address this need, we describe a systematic approach for quantifying the impacts of uncertainty on scenario-based management policy. We use relative assessment to quantify the impacts of uncertainty on scenario ranking. We illustrate our approach by considering uncertainty in parameter values and input data, with specific examples drawn from the Florida Everglades restoration project.

Results/Conclusions Our examples focus on two alternative 30-year hydrologic management plans that were ranked according to their overall impacts on wildlife habitat potential. We tested the assumption that varying the parameter settings and inputs of habitat index models does not change the rank order of the hydrologic plans. We compared the average projected index of habitat potential for four endemic species and two wading-bird guilds, to rank the alternative plans. Our analysis accounted for uncertainty in field-based parameter settings as well as drastic changes in water level inputs that simulate strong deviations from historic climate conditions. Indices of habitat potential were based upon projections from spatially explicit models that are closely tied to Everglades hydrology. Our analysis revealed striking differences in how the models responded to different types of uncertainty. We found that the rank order of the hydrologic plans was unaffected by substantial variation in the parameters of the reproductive model for the American alligator. By contrast, simulated major shifts in water levels led to reversals in the ranks of the hydrologic plans in 24.1% to 30.6% of the projections for the wading bird guilds and several individual species. Also, the relative impact of climate on habitat potential differed among the species and changed with geographic scale. By exposing the differential effects of uncertainty, relative assessment can help resource managers assess the robustness of scenario choice in model-based policy decisions.