value ecosystem services is imperfect. Difficulties in generating precise estimates of the value of ecosystem services may arise from insufficient ecological knowledge or data, lack of precision in economic methods or insufficient economic data, or lack of integration of ecological and economic analysis.
Nonetheless, the current state of both ecological and economic analysis and modeling in many cases allows for estimation of the values people place on changes in ecosystem services, particularly when focused on a single service or a small subset of total services. Use of the (imperfect) information about these values is preferable to not incorporating any information about ecosystem values into decision-making (i.e., ignoring them), since the latter effectively assigns a value of zero to all ecosystem services.
There is a much greater danger of underestimating the value of ecosystem goods and services than over-estimating their value. Underestimation stems primarily from the failure to include in the value estimates all of the affected goods and services and/or all of the sources of value, or from use of a valuation method that provides only a lower bound estimate of value. In many cases, this reflects the limitations of the available economic valuation methods. Over-estimation, on the other hand, can stem from double-counting or from possible biases in valuation methods. However, it is likely that in most applications the errors from omission of relevant components of value will exceed the errors from over-estimation of the components that are included.
SYNTHESIS OF MAJOR CONCLUSIONS
The preceding general premises collectively imply that ecosystem valuation can play an important role in policy evaluation and policy and resource management decisions. The following section provides a synthesis of the major conclusions regarding ecosystem valuation that emerge from the previous chapters. It is important to note that this is not intended to replicate or simply restate individual chapter summaries or the conclusions and recommendations of the individual chapters; rather, it is intended to integrate and summarize the broad themes that emerge from these chapters. The synthesis is organized around these three sets of related questions:
What is meant by the value of ecosystem services? What components of value are being measured?
Why is it important to quantify the value of ecosystem services (i.e., to undertake valuation)? How will the values that are estimated (i.e., the results of the valuation exercise) be used?
How should these values be measured? What methods are available for quantifying values, and what are their advantages and disadvantages?