Читать книгу North American Agroforestry - Группа авторов - Страница 81

Agroforestry offers a means of regaining some of the structural and functional characteristics that contribute to the sustainability of natural ecosystems that have been lost in the conversion of those ecosystems to homogeneous agroecosystems. An understanding of the structure and function of natural ecosystems is essential to the successful implementation of agroforestry if we wish to create more heterogeneous agroecosystems.

A complete knowledge of the many ecological processes and interactions responsible for a natural system’s sustainability will always elude us—an ecosystem is just too complex. However, perennialism and a high proportion of area in mid‐ to late‐successional states is the usual condition of natural ecosystems and an obvious goal in designing a sustainable agroecosystem. We are making progress in determining how to meet that goal, but there is much left to be learned in both basic and applied ecology. With respect to the inclusion of ecological principles within the broad field of agroforestry, some important areas warranting further research include: (a) the evaluation of net primary productivity (NPP = increment + litterfall + herbivory + mortality) for all types of agroforestry systems in different geographical regions; (b) the continued study of C sequestration and the emission of greenhouse gases such as CO₂, N₂O, and CH₄ in agroforestry systems; (c) the study of belowground interactions and processes in the realm of microbial ecology, root competition, and mycorrhizal associations; (d) the study of both positive and negative interactions among trees, shrubs, grasses, and forbs in agroforestry systems; (e) the implementation of long‐term, system‐level experiments and on‐farm demonstrations including stronger and more specific economic analyses that include the value of all ecological goods and services; (f) the study of albedo—reflectance changes occurring at the landscape level as a result of agroforestry adoption that may have implications for global warming and C sequestration scenarios; (g) a comprehensive evaluation of the biology and economics of agroforestry on a variety of sites; (h) the study of all aspects of silvopastoral systems especially as they relate to potential lowering of wood quality and value, forest regeneration, greenhouse gas emissions, and the issue of animal welfare; (i) a continued screening of useful pharmaceutical and other chemical products from forest farming systems; and (j) a comprehensive evaluation of conservation biology principles—how can we incorporate information gleaned from natural forest systems that remain in our agricultural landscapes into agricultural systems that embrace woody perennials? A better appreciation of the ecosystem and environmental services provided through agroforestry would lead to the development of rigorous environmental and economic assessments and eventually to modification of community tax structures and environmental legislation.

The ecology of highly managed agroforestry systems is becoming better understood although much remains to be done. Two recent texts on the ecology of agroforestry systems (Batish, Kohli, Jose, & Singh, 2008; Jose & Gordon, 2008) present up‐to‐date research results on ecological interactions, belowground ecological processes, resource allocation and partitioning, and the modeling of these in both tropical and temperate agroforestry systems.