Biological soil crusts, composed of primitive plants growing in and on the soil surface, cover large areas of the ground in semi arid regions where taller plant cover is scarce. They play important roles in the ecology, hydrology and soil stability of such regions. In SE Spain the crusts vary with climate and also in the extent to which they protect soils from erosion. A research project (PECOS) is currently investigating the distribution and dynamics of these crusts in SE Spain using a variety of survey, monitoring and experimental approaches. Project work is concentrated in the El Cautivo badlands near to Tabernas in Almeria and is mainly carried out in small plots of 1x1 to 5x2m. If we can extrapolate the information we gain from plots to the scale of slopes and catchments, then we will be in a much better position to understand the roles that these custs play in the broader landscape and also to predict the likely impact on these functions of changes in land use and climate. Spectral signatures of crusts suggest that the main types can potentially be distinguished from one another and from bare soils using hyperspectral data and thus, in order inestigate extrapolation between scales, we require high resolution airborne imagery, photography and digital elevation model data.