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Zusammenfassung:
Global model estimates of soil carbon changes from past land-use changes remain uncertain. We develop an approach for evaluating dynamic global vegetation models (DGVMs) against existing observational meta-data on soil carbon changes following land-use change. Using the DGVM JSBACH, we perform idealized simulations where the entire globe is covered by one vegetation type, which then undergoes a land-use change to another vegetation type. We select the grid cells that represent the climatic conditions of the meta-data and compare the mean simulated soil carbon changes to the meta-data. Our simulated results show model agreement with the meta-data on the direction of changes in soil carbon for some, but not all land-use changes, while the magnitude of simulated changes is smaller than in the meta-data. The conversion of crop to forest results in soil carbon gain of 10 % and that of forest to crop to a loss of −15 % compared to a gain of 42 % and loss of −40 %, respectively, in the meta-data. However, the conversion of crop to grass results in a small soil carbon loss (−4 %), while the meta-data indicate a gain in soil carbon of 38 %. These model deviations from the meta-data are substantially reduced by explicitly accounting for crop harvesting and switching off burning in grasslands in the model. We conclude that our idealized simulation approach provides an appropriate framework for evaluating DGVMs against meta-data and that this evaluation helps to identify the causes of deviation of simulated soil carbon changes from the meta-data
