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 extension staff, who prescribe the removal of all trees, and farmers, who, traditionally, leave trees scattered in fields. Using data on tree-crop interactions from Zimbabwe, we have used the STELLA model to simulate the negative ecological and economic impacts of trees on crops, and the benefits of various goods and services derived from trees (soil fertility, shade, fruits, etc.). The value of trees in fields generally decreased with increased rainfall and with increased fertiliser inputs. The model only supports the extensionists' recommendations that trees should be removed from fields in the case where farmers can use high inorganic fertiliser levels, and for high 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 where rainfall is low. (C) 2000 Elsevier Science B.V. All rights reserved.