Multi-scale and cross-scale assessments of social-ecological systems and their ecosystem services

It is often either undesirable or unfeasible to conduct an assessment of ecological or social systems, independently or jointly, at a single scale and resolution in time and space. This paper outlines the alternatives, which include 'multi-scale assessments' (conducting the assessment at two or more discrete scales) and 'cross-scale assessments' (multi-scale assessments which deliberately look for cross-scale interactions), and points to some methods which may be useful in conducting them. The additional work and complexity that result from taking a multi-scale or cross-scale approach, while necessary and realistic, needs to be managed. This can be achieved by the informed choice of scales, a priori consideration of the scale-related properties of the phenomena being assessed, and paying attention to the ways in which information and control pass between scales. The conceptual issues associated with choosing the scales and resolutions at which to work are discussed, as are strategies for aggregation and disaggregation and for linking studies at different scales.