Agroforestry and the functional mimicry of natural ecosystems

This chapter examines the idea that agroforestry systems designed as structural and functional mimics of natural ecosystems could address the resource depletion and land degradation typical of conventional tillage agriculture. Four questions relating to this concept are examined. Is it necessary to mimic structure to achieve functional goals? Does perenniality inevitably imply a trade-off in productivity? Can competition be managed in synthetic polycultures of trees and crops? How can these complex farming systems be successfully managed to ensure a return to the farmer? It is concluded that, while natural ecosystems can serve as models for tighter cycling of water and nutrients, it is not necessary to assemble close structural mimics to achieve functional goals, and the altered soil and water conditions of most agricultural landscapes reduce the relevance of the pre-agricultural plant communities as models. Second, natural ecosystems tell us nothing about maximising harvestable product. We must turn to other strategies to ensure agroforestry systems are productive, notably artificial breeding aud selection in the search for high-value products and services. Third, in mixtures of woody and herbaceous plants, competition tends to rule, particularly in the water-limited environments typical of southern Australia, and trees tend to win, requiring careful design and management of the interactions between trees and crops. Fourth, in terms of adoption and management, woody perennial systems are less flexible than conventional agriculture, have longer lag time to returns and higher investment costs, and are less easily trialled. While these obstacles are not insurmountable, they collectively suggest that using agroforestry to mimic patch dynamics and exploit unused resources at landscape scale is more likely to achieve improved natural resource management in southern Australia than the smaller scale approach of mimicking the structure and function of natural plant communities at paddock scale.