Quantifying Uncertainty and Assessing Sensitivity in Global Mapping of Ecosystem Services

Ecosystem service valuation may be a relevant method for assisting policy makers in environmental related decisions. However, a number of problematic aspects of the calculations, including consistency of economy (e.g., purchasing price, production price, perceived value) and determining which ecosystem subservices to include (e.g. include disservices or only beneficial services), contribute to uncertainty in the final valuations. However, ecosystem service valuations currently lack 1) a quantification of total uncertainty in ecosystem service values as a result of the uncertainties in the subservices, and 2) an analysis of the relative sensitivity of total ecosystem service values to uncertainties in various subservices.  

In a previous study, we have computed a spatial distribution of global ecosystem services by disaggregating production values over the spatial existence of each subservice by country. Nineteen subservices arranged under nine services from four categories were calculated totalling approximately 1.3 trillion international dollars for 2005. Our current study aims to perform an error propagation analysis and a sensitivity analysis of the Food Service. The Food Service, which is comprised of nine subservices, accounts for 99.8% of the total global ecosystem service value. It is extremely important to understand the reliability of the valuation of this service because it greatly contributes and overshadows the other services.

Hereto, the cattle and sheep indicators in the Livestock Subservice and the apple orchard indicator in the Fruit Subservice are analyzed. The Livestock Subservice accounts for the majority of the Food Service and is comprised of cattle, sheep, buffalo, poultry, pig, and goat. The cattle and sheep indicators have three main sources of uncertainty: the animal weight, the production value, and the number of animals per hectare for meat versus the number of animals for dairy use. The uncertainty in animal weight varies considerably by species and is important because the production value is the international dollar per live-weight ton. The production values are published with designations as either a direct calculation or an estimated figure. In the case of animal population data, RMSE were provided as part of the data release.

The Fruit Subservice is the fourth largest contributor to the total Food Subservice value. It was chosen because the input data sets are different than the top three contributors to the Food Subservice (i.e. Livestock, Dairy, and Crops). The apple orchard indicator has two main sources of uncertainty: the production value and the production area. The uncertainty in the production values are qualified as unofficial figures by the data producer, while the production area followed agricultural land use, rather than mapped apple orchards.

Both an error propagation analysis of the defined uncertainties and a sensitivity analysis provide insight into the robustness into the computed ecosystem service assessment. Presenting and understanding uncertainty and sensitivity of ecosystem service assessments is consequential for incorporating ecosystem service assessments into climate change mitigation strategies.