Agroforestry encompasses a set of land use practices which aim to realize the benefits from growing woody and herbaceous species together, commonly by the addition of trees to land already being used for pasture or for growing annual crops. It thus concerns the ways in which the presence of a plant can change the environment of its neighbours, generating a favourable balance between negative and positive plant interactions, and thereby increasing total yield, reducing yield variance and conserving resources. These ecological issues include a time dimension, and are akin to socioeconomic concepts regarding productivity, stability and sustainability in marginal land use systems. In this review, theories regarding interspecific and intraspecific interactions, and the mechanisms concerned, have been used as a basis for interpreting the results of experimental studies in agroforestry, in order to gain an understanding of the processes that determine productivity and its maintenance in these systems. The review is presented in 3 main sections. The first considers agroforestry in the context of ecological principles concerning interactions between species and the ways in which the presence of a plant can change the environment of its neighbours. The second section uses the conceptual framework developed to appraise concisely published research findings, under the headings competition, predation, mutualism and commensalism. The third section elaborates 3 key issues connected with the objectives of agroforestry: overyielding; the reduction of yield variance; and maintenance of resources.
Agroforestry Abstracts (1993) 6 (2) 57-91