- Visiting scientist and consultant, Rubber Research Institute of Malaysia (1979, 1980)
- Consultant to the Water Research Commission of South Africa, 1986
- Scientific expert and consultant to the European Commission, Fourth Framework Programme, 1995-1997
- NATO Research Fellow at the University of Washington, Seattle, USA, 1987-1988
- Consultant to the United Nations, FAO in China (1996)
- Member of the Scientific Advisory Board of the Office National des Forets, France (2000-2004)
- Regular member of scientific evaluation commissions for the French INRA and INSERM-IFR research institutes of Nancy, Montpellier, Clermont-Ferrand, Bordeaux, and others
- Chair of the Comité d’Evaluation du Département EFPA, INRA, France (2007-2008)
- Chair of the Comité d’Evaluation de l’Unité EEF INRA-Nancy, France (2012)
- Chair of the Standing Committee LESC of the European Science Foundation
- Member of the Federal Council for Sustainable Development (until 2018)
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- Scientific Peer Review Panels on ‘Terrestrial Carbon Sequestration Using the Poplar’ and ‘Carbon Processes Research’, Oak Ridge Institute for Science and Education, US Department of Energy, Washington DC, USA (2002, 2006)
- Member of the ad hoc BERAC Committee of the US Department of Energy, Washington DC, USA (2007).
- Member of the ad hoc Network Review Committee and Review Panels of the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) (2005-2007)
- Member of the evaluation committee of the Spearhead projects of the University of Eastern Finland (2010-2013)
- Regular member of the ad hoc Environment Expert Panel of the Research Council for Biosciences and Environment, Academy of Finland, Helsinki (2006, 2007, 2008, 2011)
- Member of the Steering Group of the Core Model Programme, Forest Commission, United Kingdom
- Member of the Standing Committee (since 2003) and of the Core Group (since 2006) of LESC, European Science Foundation, Strasbourg
- Occasional reviewer or scientific evaluator for various research programmes and grant committees in the USA, The Netherlands, France, Germany, South-Africa, Israel, Czech Republic, United Kingdom, Finland, and others
- Occasional reviewer for NSF, USA and for the Department of Energy, USA
- Member & Vice-chair of the Scientific Commission B4 (Applied Biological Sciences and Environmental Technology), Fund for Scientific Research – Flanders (2000-2009)