1. Department of Land Economy; University of Cambridge; 19 Silver Street Cambridge CB3 9EP United Kingdom
2. CESAER, AgroSup Dijon; INRA, University Bourgogne Franche-Comté; 26, Boulevard Petitjean, F-21000 Dijon France
3. CRED; University Paris II Panthéon-Assas; 12 Place du Panthéon, 75 231 Paris Cedex 05 France