Vegetation patterns as biological indicators for identifying runoff and sediment source and sink areas for semi-arid landscapes in Spain

The rationale behind this research concerns the need to better understand relationships between vegetation characteristics and hydrological processes. Changes in vegetation patterns could provide sensitive indicators of both desertification and water availability. This paper presents a methodology to use vegetation-bare soil patterns as indicators for identifying the extent, distribution and connectivity of runoff and sediment source and sink areas. During field studies it has been found that biological indicators can be used as evidence that areas are functioning as a source or sink for runoff and sediment. It has also been found that the locations of such source and sink areas are tightly linked to the spatial distribution of vegetation patches within the vegetation-bare soil mosaic. Therefore, patterns in vegetation and soil can be important indicators for ecosystem health and hillslope hydrology. Four pattern indices are introduced to describe the degree of contagion and bare area distribution within the vegetation mosaic and the degree of connectivity between different source areas. Binary pattern maps retrieved from a digital aerial photograph are used as examples to illustrate the behaviour of the indices. It is concluded that the indices yield important information on the spatial structure of the patterns studied and can be used to understand the interactions between pattern and its underlying processes.