Soil function assessment: review of methods for quantifying the contributions of soils to ecosystem services

Soils and their functions are critical to ensure the provision of various ecosystem services (ES). Many authors nevertheless argue that there are a lack of satisfactory operational methods for quantifying the contributions of soils to the supply of ES. In this study, we review ES mapping studies that have taken the roles of soils in ES supply into account, and propose soil function assessment (SFA) methods approved by German Federal States in spatial planning procedures to use in assessments of ES supply. We found 181 ES mapping studies in which the roles of soils in ES supply were considered. At least one soil property was used as an indicator of soil-related ES in 60% of the publications, and 13% of the publications were mainly focused on the roles of soils in supplying ES. More than two soil functions were considered in a minority of cases, indicating that the multi-functionality of soils has barely been taken into account in previous ES studies. Several decades ago, the soil science community has adopted the concept of soil functions to bring different aspects of soil to the fore and to emphasize the multi-functionalities of soils and their vastly different chemical, physical, and biological properties. We provide a set of approved SFA methods that cover the multi-functionalities of soils and are applicable to ES supply assessments. We propose that this set of operational SFA methods is a starting point for quantifying how soil systems underpin the supply of a wide range of ES. The minimal soil dataset required for these SFA methods is relatively small, and much progress has been made nationally and globally over the last decade in improving soil data infrastructure and online access for end users. These improvements will facilitate the incorporation of SFA into ES studies and thereby improve information for land use decisions. We recommend that ES assessments include the essential and multifunctional roles of soils to promote sustainable land use.