The role of trees in agroforestry: Some comments

In agroforestry land use systems, the woody perennial components ('trees') play a role in both productivity and sustainability. Some general characteristics of woody perennials are outlined and the need to consider the possible advantages or disadvantages of these in relation to specific agroforestry systems is emphasized. In deciding about introducing trees on farm land the challenge is to answer the questions: What trees? How many? How are they best arranged? Answers to the first of these will arise from the many existing and planned trials with multipurpose trees now being established worldwide. This paper addresses mainly the second question: How many trees?

Three-dimensional diagrams are used to illustrate the effects of a replacement series (tree-crop, crop-tree) on changes in total productivity and soil status with time. The types of response surfaces produced are discussed and various 'scenarios' shown to illustrate the value of this approach. Such diagrams are less a predictive tool than a means of comprehending the plant and environment changes involved.

The final section briefly discusses tree/shrub arrangement, which will depend on management considerations, soil/water conservation needs, and biological aspects of optimizing productivity. (author)