During the last few decades, land use changes have largely affected the global warming process through emissions of CO2. However, C sequestration in terrestrial ecosystems could contribute to the decrease of atmospheric CO2 rates. Although Mediterranean areas show a high potential for C sequestration, only a few studies have been carried out in these systems. In this study, we propose a methodology to assess the impact of land use and land cover change dynamics on soil organic C stocks at different depths. Soil C sequestration rates are provided for different land cover changes and soil types in Andalusia (southern Spain). Our research is based on the analysis of detailed soil databases containing data from 1357 soil profiles, the Soil Map of Andalusia and the Land Use and Land Cover Map of Andalusia. Land use and land cover changes between 1956 and 2007 implied soil organic C losses in all soil groups, resulting in a total loss of 16·8 Tg (approximately 0·33 Tg y−1). Afforestation increased soil organic C mostly in the topsoil, and forest contributed to sequestration of 8·62 Mg ha−1 of soil organic C (25·4 per cent). Deforestation processes implied important C losses, particularly in Cambisols, Luvisols and Vertisols. The information generated in this study will be a useful basis for designing management strategies for stabilizing the increasing atmospheric CO2 concentrations by preservation of C stocks and C sequestration. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract. Soil C sequestration through changes in land use and management is one of the sustainable and long-term strategies to mitigate climate change. This research explores and quantifies the role of soil and land use as determinants of the ability of soils to store C along Mediterranean systems. Detailed studies of soil organic C (SOC) dynamics are necessary in order to identify factors determining fluctuations and intensity of changes. In this study, SOC contents from different soil and land use types have been investigated in Andalusia (Southern Spain). We have used soil information from different databases, as well as land use digital maps, climate databases and digital elevation models. The average SOC content for each soil control section (0-25, 25-50 and 50-75 cm) was determined and SOC stocks were calculated for each combination of soil and land use type, using soil and land cover maps. The total organic C stocks in soils of Andalusia is 415 Tg for the upper 75 cm, with average values ranging from 15.9 Mg C ha −1 (Solonchaks under "arable land") to 107.6 Mg C ha −1 (Fluvisols from "wetlands"). Up to 55 % of SOC accumulates in the top 25 cm of soil (229.7 Tg). This research constitutes a preliminary assessment for modelling SOC stock under scenarios of land use and climate change.

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European policies can be relevant to protect soils under climate change scenarios and therefore preserve the wide variety of functions and services provided by the soil. The European Thematic Strategy for Soil Protection will require member states to identify areas under risk from various soil threats and establish procedures to achieve sustainability. Five models Terraza, Cervatana, Sierra, Raizal, and Pantanal included in the Mediterranean Land Evaluation Information System decision support system packages were used to identify areas vulnerable to various soil threats under climate change scenarios in the Andalusia region. While Terraza and Cervatana forecast general land use capability for a broad series of possible agricultural uses, the Sierra model predicts forestry land suitability for the presence/absence of 22 typical Mediterranean forest species. Raizal and Pantanal models predict soil erosion vulnerability, contamination, and other processes. Interpretation of results in different scenarios allows quantifying the effects of climate change in terms of agricultural productivity, forestry land suitability, erosion, and contamination risks. The obtained results allow to identify detailed vulnerable areas and formulate site-specific management plans for soil protection. Climate change is expected to impact crop growth with a higher impact on summer crops (corn, sunflower, and cotton). The results show a potential opportunity for reforestation (Quercus spp.) in future climate scenarios, while other species such as Castanea sativa will not be suitable in the study area by 2070 and 2100. Soil contamination and erosion show only slight differences between the current and future scenario of climate change.

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