Modelling changes in soil organic matter after planting fast-growing Pinus radiata on Mediterranean agricultural soils

The Kyoto Protocol explicitly allows the storage of carbon (C) in ecosystems resulting from afforestation to be offset against a nation's carbon emissions and paves the way for carbon storage in soils to be eligible as carbon offsets in the future. More information is required about how afforestation affects carbon storage, especially in the soil. We report a study in which soil carbon storage in first-rotation Mediterranean Pinus radiata plantations, established on former cereal fields and vineyards, was measured and modelled. Measurements were made on plantations of several ages, as well as repeat measurements at the same site after 5 years. We tested the ability of two widely used soil organic matter models (RothC and Century) to predict carbon sequestration in Mediterranean forest soils. Increases in the top 5 cm of soil of about 10 g C m(-2) year(-1) were observed after afforestation of former vineyards, but nitrogen (N) either remained the same or decreased slightly. During afforestation, most organic matter accumulated in the ectorganic layers at a rate of 19 g C m(-2) year(-1) in former vineyards and 41 g C m(-2) year(-1) in former cereal fields. The RothC and Century models were sensitive to previous land use and estimated a carbon sequestration potential over 20 years of 950 and 700 g C m(-2), respectively. The accurate simulation of the dynamics of soil organic matter by RothC, together with measured above-ground inputs, allowed us to calculate below-ground inputs during afforestation. The Century model simulated total C and N, including the ectorganic horizons, well. Simulations showed a depletion of N in the below-ground fractions during afforestation, with N limitation in the former vineyard but not on former cereal land. The approach demonstrates the potential of models to enhance our understanding of the processes leading to carbon sequestration in soils

Validated, representative soil carbon profiles under forest vegetation

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Soil carbon in Mediterranean ecosystems and related management problems

16CBT: S-D-2450reservedInternational coauthor/editorThe 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.mixedRodeghiero, M.; Rubio, A.; Díaz-Pinés, E.; Romanyà, J.; Marañón-Jiménez, S.; Levy, G.J.; Fernandez-Getino, A.P.; Sebastià, M.T.; Karyotis, T.; Chiti, T.; Sirca, C.; Martins, A.; Madeira, M.; Zhiyanski, M.; Gristina, L.; Lamantia, T.Rodeghiero, M.; Rubio, A.; Díaz Pinés, E.; Romanyà, J.; Marañón Jiménez, S.; Levy, G.J.; Fernandez Getino, A.P.; Sebastià, M.T.; Karyotis, T.; Chiti, T.; Sirca, C.; Martins, A.; Madeira, M.; Zhiyanski, M.; Gristina, L.; Lamantia, T

Impact of Land Use and Land Cover Changes on Organic Carbon Stocks in Mediterranean Soils (1956-2007)

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 16·8Tg (approximately 0·33Tg y-1). Afforestation increased soil organic C mostly in the topsoil, and forest contributed to sequestration of 8·62Mgha-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