On the Definition of the Natural Capital of Soils: A Framework for Description, Evaluation, and Monitoring

The unknown consequences and potential impacts of mankind’s ability to destroy, alter, or manipulate ecosystems on a vast scale drives our need to better understand the earth system. A fundamental challenge for soil science in the 21st century is to understand the role of soil processes in relation to the function of the earth system. Th e rationale for developing a defi nition of soil natural capital stems from the premise that we value ‘things’ based on their perceived value to human well-being. As a consequence, ignorance of the value of a resource, or system, may lead to its neglect and omission from decision making. Th erefore, there is a need to develop a defi nition of soil natural capital, fi tting within a broad framework, which can be used to assess soil ecosystem services that contribute to the function of the earth system. Th ough various defi nitions of soil natural capital have been proposed, mostly in the agricultural context, it still remains a nebulous and ill-defi ned term. Th e objective of this paper is to develop an embracing defi nition of soil ‘natural capital’ focusing on (i) mass, (ii) energy, and (iii) organization/entropy. Mass is further subdivided into solid, liquid and gas phases, and organization into physicochemical, biotic, and spatiotemporal structure. We diff erentiate between two aspects of capital, the quantity and the quality. As a result of our defi nition, soil moisture, temperature, and structure emerge as valuable stocks, alongside the more traditionally viewed stocks such as inorganic (mineralogy, texture) and organic materials (OM content). We go on to demonstrate how natural capital fi ts within the ecosystem services framework, and how using integrated valuation and process based models it can be evaluated. Finally we discuss measurement and monitoring needs that fi t with this vision of evaluation.