Forest soils : Carbon stocks in Swiss forest soils

The “Forest soils” project explored the factors controlling soil organic carbon storage in Swiss forest soils by evaluating 1000 soil profiles. Results showed that climate and physico-chemical soil properties had a strong effect on soil carbon storage, while historical land use was less important.

  • Background completed research project)

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    Soil organic matter (SOM) plays a key role for many soil functions. It is the most important carbon pool of terrestrial ecosystems and it affects nutrient cycling, microbial diversity and pollutant dynamics. SOM is vulnerable as it gains carbon from litter inputs and loses carbon through decomposition. Although individual processes of SOM dynamics have been identified experimentally, there is a limited quantitative understanding of how climate, land use and soil properties are affecting soil organic carbon storage.

  • Aim

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    The aim of the project was to identify the main determining factors of carbon storage in Swiss forest soils, climate, historical land-use and physico-chemical soil properties. In this context, the researchers analysed more than 1,000 soil samples from Swiss forests.

  • Results

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    The reconstruction of forest development for about 850 currently forested sites using historical maps showed that forest age has only a small effect on soil carbon stocks. The analysis along climatic gradients showed a higher content of particulate potentially labile organic matter under cold and moist conditions. In comparison, mineral-bound organic matter was hardly related to climatic parameters. These results suggest that a warmer and drier climate could induce losses of soil organic matter, especially at higher altitudes with thick organic layers. The soil carbon storage predicted with the YASSO model showed large discrepancies with measured stocks. The residual analysis indicated that physico-chemical soil properties determining carbon stabilisation are not adequately represented in the model.

  • Implications for research

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    The project contributes to an improved understanding of soils as a source and sink of CO2 and it provides the data for a more detailed modelling of the carbon cycle.

  • Implications for practice

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    The results will improve the greenhouse gas inventory that Switzerland is compiling as part of its commitment to the Kyoto international climate agreement.

  • Original title

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    SOM control: Controls on soil organic matter in Swiss forest soils: The impact of forest productivity, land-use history, climate and physico-chemical stabilization