1. Dep. of Economics Swedish Univ. of Agricultural Sciences P.O. Box 730 S‐220 07 Lund Sweden
2. Dep. of Biology and Centre for Environmental and Climate Research Lund Univ. Sölvegatan 37, 223 62 Lund Sweden
3. Biometris Dep. of Mathematical and Statistical Methods P.O. Box 16 6700 AA Wageningen the Netherlands
4. Dep. of Ecology Philipps Univ. Karl‐v.‐Frisch‐Str. 8 35043MarburgGermany
5. Columbia Basin Agricultural Research Center Oregon State Univ. P.O. Box 370 PendletonOR97801
6. Dep. of Soil and Environment Swedish Univ. of Agricultural Sciences P.O. Box 7014 S‐750 07 Uppsala Sweden
7. Helmholtz Centre for Environmental Research Theodor‐Lieser‐Straße 4 06120HalleGermany
8. Dep. of Agroecology Aarhus Univ. Blichers Allé 20, P.O. Box 50 DK‐8830 Tjele Denmark