Carbon stocks in soils

The Centre for Ecological Research and Forestry Applications (CREAF), the Forest Sciences Center of Catalonia (CTFC) and the Autonomous University of Barcelona have published what they claim to be the most precise estimation of soil organic carbon (SOC) in forests, shrub lands and grasslands of peninsular Spain to date.

The study, published in Biogeosciences, was based on the quantitative modelling of the main variables affecting soil C stocks, including vegetation cover, soil characteristics and climate. The total amount of SOC estimated in this study represents 3.3% of the total SOC of Europe’s forests and approximately four times the C stocks of Spanish forest biomass.

The assessment was based on field measurements of more than 900 soil profiles. SOC was modelled to a depth of 1m and the resulting statistical model was used to estimate SOC in the next to 8 million pixels of the Spanish Forest Map.

In the studied area, the main variables influencing the spatial distribution of SOC were climate and vegetation cover. Total annual precipitation and mean annual temperature showed a positive and negative effect on the total amount of SOC respectively, while the interaction between elevation and temperature was also significant.

Mixed broadleaf forests and evergreen woodlands were associated with the lowest SOC values, whereas the highest values corresponded to deciduous broadleaf forests, mixed forests and grasslands. The influence of climate on soil C stocks could be related to the role of soil microorganisms in SOC stability, as the soil microflora is highly sensitive to moisture and decompose organic matter more rapidly with increasing temperature. In consequence, climate change may play an important role in the C loss of forest soils. Moreover, forest deforestation could result in greater soil C losses in wet continental and mountainous areas than in semiarid and lowland Mediterranean areas. In any case, the present study represents a statistical source of information and temporal variations in SOC should be cautiously considered.

The study is very significant to Spain as a nation that needs to assess the stocks and fluxes of C, including SOC estimates. The SOC estimates presented in this study provide a baseline to improve our ability to respond to environmental changes by informing land use management schemes considering that SOC storage is a long term process and the rate off soil C loss could be increased by incorrect forest management.

More information (Spanish)

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