norm (Nair, 1989; Sinclair, 1999; Newman and Gordon, 2018). However, many authors use the words “practice” and “system” interchangeably (Table 2–1) as in this volume. Agroforestry classification in the United States and Canada has evolved from agricultural traditions wherein an agricultural production system is an aggregation of various practices. Under this form of classification, agroforestry is most often recognized as a set of practices which are incorporated, along with other appropriate practices, into agricultural systems likes pieces of a puzzle fitting together at a variety of spatial scales (i.e., field, farm, watershed, landscape).
Criteria
Four key criteria characterize agroforestry practices in the United States and Canada and distinguish them from other practices (Merwin, 1997). To be called agroforestry, a land use practice must satisfy all of the following four criteria:
Intentional
Combinations of trees, crops, and/or livestock are intentionally designed, established and/or managed to work together and yield multiple products and benefits, rather than as individual elements which may occur together but are managed separately.
Intensive
Agroforestry practices are created and intensively managed to maintain their productive and protective functions, and often involve cultural operations such as cultivation, fertilization, irrigation, pruning and thinning.
Integrated
Components are structurally and functionally combined into a single, integrated management unit tailored to meet the objectives of the landowner. Integration may be horizontal or vertical, and above‐ or below‐ground. Integration of multiple crops utilizes more of the productive capacity of the land and helps balance economic production with resource conservation.
Interactive
Agroforestry actively manipulates and utilizes the biophysical interactions among components to yield multiple harvestable products, while concurrently providing numerous conservation and ecological benefits.
Practices
Six categories of agroforestry practices (Table 2–2) that embody the above criteria are recognized in the United States and Canada by the Association for Temperate Agroforestry–AFTA (Merwin, 1997). The sixth agroforestry practice, urban food forests, has emerged over the past decade (Munsell et al., 2022).
Riparian and Upland Buffers
Riparian and upland buffers are strips of permanent vegetation, consisting of trees, shrubs, and grasses that are planted and managed together. Riparian buffers are placed between agricultural land (usually crop land or pastureland) and water bodies (rivers, streams, creeks, lakes, wetlands) to reduce runoff and non‐point source pollution, stabilize streambanks, improve aquatic and terrestrial habitats, and provide harvestable products. Upland buffers are placed along the contour within agricultural crop lands to reduce runoff and non‐point source pollution, improve internal drainage, enhance infiltration, create wildlife habitat and connective travel corridors and provide harvestable products.
Windbreaks
Trees or shrubs are planted as barriers to reduce wind speed. Windbreak practices include shelterbelts, timberbelts and hedgerows. Windbreaks are planted and managed as part of a crop or livestock operation. Field windbreaks are used to protect a variety of wind‐sensitive row, forage, tree, and vine crops, to control wind erosion, and to provide other benefits such as improved bee pollination of crops and wildlife habitat. Livestock windbreaks help reduce animal stress and mortality, feed and water consumption, and odor. Timberbelts are managed windbreaks designed to increase the value of the forestry component.
Table 2–2. Six categories of agroforestry practices in the US and Canada.
| Practice | Predominant Region (s) | Use(s) | Associated Technologies |
|---|---|---|---|
| Riparian and upland buffers | All Regions | Ameliorate nonpoint source pollution, abate soil erosion and nutrient loading, protect watershedsModify microenvironments and protect aquatic habitats | Streambank bioengineeringConstructed wetlandsGreen infrastructure |
| Windbreaks | Great Plains, All Regions | Protect and enhance production of crops and animals, control soil erosion, distribute snowfall.Trap snow. | Living snow fences |
| Alley cropping | Midwest, All Regions | Increases and diversifies farm crops and income | Plantation management |
| Silvopasture | West, Southeast, All Regions | Economic diversification, improve animal health, create wildlife habitat, fire protection, timber management | Pine straw harvest |
| Urban Food Forests | All Regions | Diverse urban food production, soil health and diversity, human health, nutrition and well‐being, environmental and social justice benefits, education, community | Permaculture |
| Forest farming | All Regions | Income diversification | Forest management |
Alley Cropping
This practice combines trees planted in single or multiple rows with agricultural or horticultural crops cultivated in the alleyways between the tree rows. High‐value hardwoods such as oak (Quercus sp.), walnut (Juglans sp.), chestnut (Castanea sp.) and pecan (Carya illinoensis (Wangenh.) K. Koch) are favored species in alley cropping practices, and many can provide high‐value lumber or veneer logs. Crops grown in the alleys, and nuts from walnut, chestnut and pecan trees, provide annual income from the land while the longer‐term wood crop matures (Gold, 2019). When specialty crops such as herbs, fruits, vegetables, nursery stock, or flowers are grown in the alleys, the microclimate created by the trees enables the economic production of these sensitive high‐value crops in stressed environments.
Silvopasture
This practice combines trees with forage (pasture) and livestock production. Silvopasture can be established by adding trees to existing pasture, or by thinning an existing forest stand and adding (or improving) a forage component (Jose et al., 2017). The trees are managed for high‐value sawlogs, and at the same time they provide shelter for livestock, protecting them from temperature stresses and reducing food and water consumption. Forage and livestock provide short‐term income at the same time a crop of high‐value sawlogs is being grown, providing a greater overall economic return from the land.
Forest Farming
High‐value specialty crops are cultivated under the protection of a forest overstory that has been modified and managed to provide the appropriate microclimate conditions. Shade‐tolerant specialty crops like ginseng (Panax quinquefolium