Use of ecosystem information to improve soil organic carbon mapping in a Mediterranean island.

Detailed maps of soil C are needed to guide sustainable soil uses and management decisions. The quality of soil C maps of Italian Med- iterranean areas may be improved and the sampling density reduced using secondary data related to the nature of the ecosystem. The current study was conducted to determine: (i) the improvements ob- tainable in mapping soil C over a Mediterranean island by using eco- system features and (ii) the effect of different sampling densities on the map accuracy. This work relied on field sampling (n 5 164) of soil properties measured over the island of Pianosa (Central Italy). Sta- tistical analysis assessing the relationship between soil properties and ecosystem features revealed that the conceptual model of ecosystems defined on the basis of environmental features such as vegetation cover, land use, and soil type was mainly related to the variation of soil organic carbon (OC) content and to the type of Mediterranean envi- ronment. The distribution of ecosystems was used to improve the accuracy of soil OC maps obtainable by a simple interpolation approach (ordinary kriging). Substantial improvement was obtained by: (i) stratification into ecosystem types and (ii) applying locally calibrated regressions to satellite imagery that introduced both inter- ecosystem and intra-ecosystem information linked to vegetation features. This study showed that interpolation methods using in- formation on ecosystem distribution can produce accurate maps of soil OC in Mediterranean environments, mostly because of the linkage between soil OC and vegetation types, which are spatially fragmented and heterogeneous.