Maximizing conserved biodiversity: why ecosystem indicators and thresholds matter

Accounting for biodiversity is important in several different types of constrained choice problems, including public and private decisions for habitat and species conservation, the establishment of recreational parks and natural areas, mitigation banking, and natural resource damage assessment (particularly primary and/or compensatory restoration planning and scaling). In such applications it is important to give careful consideration to (1) the choice of biodiversity indicator(s) to be used, and (2) the role of discontinuous, nonlinear ecological processes in light of the decisionmaker's chosen time horizon. The former is important because the choice of indicator(s) can substantially influence decisions about conservation priority-setting and planning. The latter is critical for the same reason, notwithstanding that dynamic ecosystem processes have rarely been considered sufficiently, if at all, in such applications (in part because the processes usually are poorly understood or measured). In this manuscript we use avian diversity data, collected by one of the authors, from hardwood forest ecosystems in the eastern United States. We couple these data with estimates of species prevalence factors to construct a case study of how indicator choice and consideration of ecological thresholds influence the outcomes of biodiversity preservation problems. We show that (1) the choice of indicator(s) is critical, (2) failure to account for nonlinear, threshold effects in an ecosystem's future progression alters preservation decisions and ignores important information, (3) the effect or choosing different time horizons depends on the indicator used, and (4) for any given biodiversity indicator, dynamic solutions can depend on the time horizon chosen but not necessarily in monotonic or simple fashion. Our case study highlights the importance of further system-specific research on dynamic ecological progressions as well as uncertainty regarding future supply and demand for ecosystem service flows. (C) 2001 Elsevier Science B.V. All rights reserved.