Ecological aspects of temperate agroforestry systems: An overview

Background/Question/Methods

Sixty three percent of the forest land in the US is privately owned. Excluding the low- productivity forests and those in reserve, 71% of the remaining high-productivity forest is privately owned. As a result, for conservation efforts to work and for forest ecosystem services and biodiversity to be protected, large portion of private forest landowners, many of them nonindustrial, must be involved. Pressure on much of the native-species-mixed forests comes from urbanization and conversion to agriculture, such as row cropping, pastureland, or monospecific tree plantations, and more recently – possible conversion to short rotations plantations for fast-growing coppiced stands for biomass production. With the spike in corn prices in recent years, many landowners have been tempted to consider converting even land formerly in the Conservation Reserve Program (CRP). CRP land, known for its valuable functions and abilities to reduce soil erosion, improve water quality and wildlife habitat, and to reduce flood damage, protects highly erodible cropland or other environmentally sensitive sites through establishing a more permanent cover, such as trees. An alternative to forest conversion to row-cropping that would still provide landowners the benefits of annual income from agricultural products, while still maintaining some ecosystem functions, are agroforestry systems.

Results/Conclusions

Agroforestry systems have been tested extensively in the States, but particularly in the tropics and Europe. They represent low density trees with agricultural annual crops or cattle grazing among the trees. Compared to naturally regenerated forests or purely agricultural fields/pastures, some of the benefits and disadvantages of agroforestry systems include: 1) more wildlife habitat and ecosystem services than an agricultural field or pastureland, but not if compared to a naturally regenerated mixed forest; 2) reduced soil erosion compared to agricultural fields; 3) faster tree growth compared to forest conditions, but there is a need for pruning; 4) potential for larger and more frequent tree seed production; 5) increased agricultural yield and less need for fertilization, 6) depending on the tree species, additional non-timber products and benefits include nuts (pecan, black walnut, chestnut, oaks), chemicals, nitrogen-fixation and livestock feed (black locust and pods), pollen and nectar for native pollinators (basswood), and carbon sequestration. The trees do not necessarily have to be from the same species or to be in rows. Use of properly designed agroforestry systems should be recommended to private landowners as an alternative to purely agricultural fields and pastures and further research in needed to better quantify ecosystem services.