The impact of windthrow on carbon sequestration in Switzerland: a model-based assessment Esther Thu ¨rig a, * , Taru Palosuo b , Ju ¨rg Bucher a , Edgar Kaufmann a a Swiss Federal Research Institute WSL, Zu ¨rcherstrasse 111, CH-8903 Birmensdorf, Switzerland b European Forest Institute (EFI), Torikatu 34, FIN-80100 Joensuu, Switzerland Received 8 June 2004; received in revised form 25 October 2004; accepted 13 February 2005 Abstract Carbon sequestered in biomass is not necessarily stored infinitely, but is exposed to human or natural disturbances. Storm is the most important natural disturbance agent in Swiss forests. Therefore, if forests are taken into account in the national carbon budget, the impact of windthrow on carbon pools and fluxes should be included. In this article the forest scenario model MASSIMO and the soil carbon model YASSO were applied to assess the effect of forest management and an increased storm activity on the carbon sequestration in Swiss forests. First, the soil model was adapted to Swiss conditions and validated. Second, carbon fluxes were assessed applying the two models under various forest management scenarios and storm frequencies. In particular, the influence of clearing after a storm event on the carbon budget was analyzed. The evaluation of the model results showed that the soil model reliably reproduces the amount of soil carbon at the test sites. The simulation results indicated that, within the simulated time period of 40 years, forest management has a strong influence on the carbon budget. However, forest soils only react slightly to changes in the above-ground biomass. The results also showed that a storm frequency increase of 30% has a small impact on the national carbon budget of forests. To develop effective mitigation strategies for forest management, however, longer time periods must be regarded. # 2005 Elsevier B.V. All rights reserved. Keywords: Windthrow; Validation; Soil organic carbon; Forest management; MASSIMO; YASSO 1. Introduction Temperate forests play an important role in the global carbon cycle (Tans et al., 1990). Their contribution ranges from accumulating biomass and acting as a carbon sink to releasing carbon in decay processes and acting as a carbon source (Houghton, 1993; Ciais et al., 1995). Compared to other European countries, the growing stock in Swiss forests is high (366 m 3 stemwood ha À1 ) and the annual increase in growing stock large (3.2 m 3 stemwood ha À1 y À1 ) (Brassel and Bra ¨ndli, 1999). This means that, at present, despite the age structure and the annual harvesting of 5.1 m 3 stemwood ha À1 , Swiss forests still accumulate above-ground biomass. Old forests potentially act as significant carbon sinks (Knohl et al., www.elsevier.com/locate/foreco Forest Ecology and Management 210 (2005) 337–350 * Corresponding author. Tel.: +41 1 739 25 52; fax: +41 1 739 22 15. E-mail address: esther.thuerig@wsl.ch (E. Thu ¨rig). 0378-1127/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2005.02.030