Summary 1. In trying to operationalize the notion of sustainable ecosystem health, ecologists have focused on identifying sets of indicators which can be used to assess river condition relative to some normative, undegraded condition. Recognition and description of this normative state has proved elusive, particularly in highly variable semiarid ecosystems. Without an operational definition of the desired system condition that reflects both scientific rigour and broader societal value systems, rivers are unlikely to be managed effectively. 2. Managing river health should not be confused with measuring it. Many monitoring or assessment programs become ends in themselves instead of being the means to achieving specific management goals. The absence of a test of the results of monitoring further introduces the risk of management by observation and ‘pseudo‐fact’. Health ‘endpoints’ provide a scientific description of management goals, while ‘values’ provide a societal perspective. Together they complement the use of indicators and provide the basis for a strategic rather than reactive approach to management. 3. The integration of value systems, endpoints and indicators of ecosystem health or ecosystem integrity forms the cornerstone of a consultative management process for the rivers of the Kruger National Park. 4. An objectives hierarchy has been developed to service management’s institutional hierarchy. ‘Vision’ and objectives serve upper levels of management with value based statements of strategic intent which have been tested against public opinion. Goals provide managers on the ground with specific ecological endpoints termed ‘thresholds of probable concern’ (TPCs). TPCs are described by a range of spatially and temporally bounded indicators of the system’s response to the main potential agents of change. 5. TPCs represent statements or hypotheses of the limits of acceptable change in ecosystem structure, function and composition. They thereby provide an inductive and strategic approach to adaptive management in a data poor situation. Integrated monitoring, research and modelling track criteria relative to TPCs and question whether management action, or recalibration of the TPC, is needed. TPCs thus provide direction for management but their validity and appropriateness are frequently challenged and adaptively modified. 6. The objectives hierarchy gives Kruger Park management a mandate to ‘maintain biodiversity in all its natural facets and fluxes’. Alluviation, as a consequence of increased sediment supply and decreased sediment transport capacity, is a major threat to the biodiversity of the bedrock‐controlled rivers which flow through the park. Thus, for example, TPCs for geomorphic diversity reflect permissible ranges of change in bedrock character of the physical template. They are measured as change in the proportion of different geomorphic units in identified representative reaches. TPCs for riparian vegetation are measured as change in population structure of selected species within the representative reaches. They reflect a likely range of biotic responses to change in the physical template. A specific set of indicators, reflecting response to the major agents of change, therefore provides a parsimonious program for assessing ecosystem condition relative to explicit goals and a clearly defined management process.
Freshwater Biology – Wiley
Published: Mar 1, 1999
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