The use of methods based on process indicators to monitor and evaluate ecosystem functioning is of scientific and applied interest due to their relatively low-cost and rapid ease of acquisition in comparison to detailed direct quantitative measures of ecosystem processes and fluxes. However, the technical potential of these indicators requires verification with multiscale measures of the represented functions before they can be reliably used. In this study at multiple spatial scales we evaluated the potential of the infiltration, stability and nutrient cycling indices utilized by the Landscape Function Analysis (LFA) methodology for describing the processes of runoff, erosion, and nutrient cycling of semiarid Mediterranean grassland-shrubland ecosystems. The accuracy and reliability of the infiltration and stability indices was tested through analyses of their relationships with quantitative multiscale records of water and sediment flows, particularly final infiltration rate and sediment concentration obtained from rainfall simulations in bare-soil and vegetation microplots, and total runoff and sediments produced during 4 years from natural rainfall in nine hillslope-plots and three catchments. The nutrient cycling index was tested using direct measures of organic carbon and soil enzyme activity.
Results/Conclusions
At the microplot scale, the functional indices correctly scaled the higher hydrological and erosional yields, and lower soil organic carbon and enzyme activity of the bare soils relative to the vegetation patches. The infiltration index was also sensitive to the internal variation in the infiltration rate of the bare soils. At the plot scale, total runoff was only related to the infiltration index of the bare soils, suggesting that the hydrological response of the plots depends mainly on the surface condition of the bare areas, while the functional status of the plant patches would be less important. The stability index was not related to plot sediment yield. At the catchment scale, the infiltration index correctly described the variability of the runoff yield. The infiltration index showed the best relationships with direct measures of the corresponding ecosystem function obtained at several scales, supporting its utility as an indicator of the hydrological functioning of semiarid Mediterranean areas.
