1. School of Geography, Politics and Sociology, University of Newcastle, Newcastle upon Tyne NE1 7RU, England
2. Institute of Forestry Economics, Albert-Ludwigs-University Freiburg, D-79085 Freiburg, Germany
3. School of Population and Health Sciences, University of Newcastle, Newcastle upon Tyne NE2 4HH, England
4. Evangelische Fachhochschule Darmstadt, Zweifalltorweg 12, D-64293 Darmstadt, Germany