Soil carbon in Mediterranean ecosystems and related management problems

The Mediterranean region can be considered as a transitional zone between sub-tropical and temperate climates, characterized by dry, hot summers and mild, wet winters. According to the FAO database the prevailing soil type in the Mediterranean region are Cambisols however Fluvisols, Luvisols and Leptosols are also quite common. In order to quantify the soil carbon content of the major Mediterranean ecosystems, a data collection was organized among the partners of the COST 639 action. Moreover, the effects of wildfires on soil carbon loss and organic matter decomposition were investigated together with inorganic contributions to CO2 soil emissions. The average soil carbon content per unit surface area, to a depth of 30 cm, was found to be around 60-70 tC ha-1 for forest and rangeland ecosystems. Lower contents were found for Dehesa and agricultural soils. However, surprisingly high values, up to 200 tC ha-1 were also reported, which seem to be quite uncommon for dry land ecosystems. The main problem in this study was defining exactly what should or should not be included into the definition of "Mediterranean climate". In fact this term is often used with a wide meaning that includes also temperate ecosystems and therefore a consistent analysis to define the baselines of soil carbon content should firstly be based on a climatic classification. For the same reason a comparison between IPCC default values for forest ecosystems and the collected data in this study was found to be difficult. Moreover, common sampling procedures should be applied to guarantee the comparability of data.