The value of mature trees in arable fields in the smallholder sector, Zimbabwe

In the smallholder sector of much of Africa, mature trees are often left in arable fields or on field margins, and there is often a conflict between e xtension staff, who prescribe the removal of all trees, and farmers, who, t raditionally, leave trees scattered in fields. Using data on tree-crop inte ractions from Zimbabwe, we have used the STELLA model to simulate the negat ive ecological and economic impacts of trees on crops, and the benefits of various goods and services derived from trees (soil fertility, shade, fruit s, etc.). The value of trees in fields generally decreased with increased r ainfall and with increased fertiliser inputs. The model only supports the e xtensionists' recommendations that trees should be removed from fields in t he case where farmers can use high inorganic fertiliser levels, and for hig h rainfall regions. However, even under these conditions, 1-2 trees ha(-1) may need to be retained for the value of shade. The model further predicts intercropping with trees where fertiliser inputs are low or absent, and whe re rainfall is low. (C) 2000 Elsevier Science B.V. All rights reserved.