Detection and measurement are necessary if land degradation is to be accurately located, its past and future trends estimated, and its impact on human welfare assessed. Detection and measurement both depend on and contribute to an understanding of the processes and phenomena of degradation, and it is only by explanation that prediction of the future course of degradation is possible.
This chapter includes a discussion of what needs to be detected and measured, considers the role of natural science in that choice, discusses the nature of explanation and prediction, and attempts to establish a framework for a discussion of processes and the space and time scales of reference to degradation. Wherever appropriate, stress is laid upon the degree to which a process is understood. The intention is to emphasise processes by which we can better understand the phenomena discussed in the first chapter.
What is to be detected and measured?
Land degradation is a change to land that makes it less useful for human beings. The concept of land is broad and, after J G Speight (nd), is the extensive system of physical and biological materials and processes associated with the interface of the solid earth, terrestrial water bodies and the air, and the works of human beings.
A change has occurred in studies of land degradation which places emphasis on the complex links between economic, social, physical and biological processes and effects, rather than identifying specific topics such as soil acidification or tree decline as the only matters of concern in studies of land degradation.