Agroforestry

Summary

Agroforestry is an interdisciplinary scientific field that combines and applies forestry and agricultural principles and techniques to create a sustainable land-use system. Agroforestry provides a wide range of ecological benefits, including improved water quality and wildlife habitat and reduced soil erosion. By combining trees and shrubs with crops and livestock, agroforestry systems attempt to optimize the benefits of short-term crop and livestock rotations and long-term forest rotations. The blending of production practices, which has occurred for centuries, allows landowners to reap the economic benefits of annual crops while waiting for forest products. In addition to financial benefits, agroforestry results in ecological benefits that may not occur in a traditional agricultural system, including forming windbreaks, wildlife corridors, and riparian buffers.

Definition and Basic Principles

In many situations, land is managed using a single-approach (or monoculture) system, such as a farm devoted solely to raising crops or livestock or a forest cultivated for pulp or lumber production. These separate approaches can be managed successfully to produce a sustainable product. However, by applying key forestry and agricultural techniques, agroforestry practitioners attempt to develop a sustainable land-use practice, producing both short-term and long-term benefits. Although many combinations of forest- and crop-livestock-management techniques exist, agroforestry typically takes the forms categorized as tree-crop, tree-animal, shelterbelt, riparian forest, and natural-specialty crop systems.

Agroforestry provides the framework for a systems approach to land management, allowing for understanding how the physical structure, ecological influences, and economic outputs of trees and forests are interconnected with those same characteristics in crops and livestock. In many climatic regions, from tropical to semiarid zones, constant cropping can place a drain on soil nutrients, eventually creating infertile land. By incorporating fallow periods in the crop rotation, farmers can replenish these soil nutrients. However, during the fallow period, no crops are produced. Depending on local policies and food-production demand, the fallow period may be excessively shortened and no longer serve its purpose. The goal of agroforestry is to incorporate deeper-rooted perennials (trees and shrubs) to maintain nutrient cycling and soil fertility so agriculture can continue for longer periods of time.

Background and History

Agroforestry as a technique for land management has been used for centuries, but it was not until the mid-1970s that the term was coined and defined. Early adoptions of what would later be defined as agroforestry incorporated the production of crops, animals, and building materials. Although there was a subsequent shift to farming and forestry focusing on monocultures, agroforestry continued to exist. In later decades, agroforestry has become an important approach to land management in developing regions of the world. Focusing on sustainable land-management practices that increase economic and ecological diversity has facilitated the survival and development of regions where heavy forestry or heavy agriculture could have destroyed resources. Because of the large economic and ecological impact on local communities, government and non-governmental organizations have expanded research since the 1990s to refine agroforestry practices and disseminate information to the public.

How It Works

Practitioners cannot assume that all forms of agroforestry will succeed in all environments. The surrounding ecological and economic environment, previous land-use practices, and goals of the manager, owner, and community all play into the success of any one of the numerous and overlapping agroforestry strategies. Although the techniques used may be structurally different, the outputs are the same: Establish an ecologically and economically sustainable system that provides short- and long-term products in the forms of agricultural crops and livestock, and tree and non-tree forestry products. The five common agroforestry systems (tree-crop, tree-animal, shelterbelt, riparian forests, and natural-specialty crops) are broad, and there is overlap between each one. Applying a specific system is typically related to the ecological and economic environment surrounding an individual owner and piece of land, which includes the selection of particular crop and tree species. Because of the broad nature of these systems, the individual goals defined by the practitioner may separate or merge the agroforestry practice being conducted, resulting in several agroforestry systems existing on a single piece of land.

Adding Trees to Agriculture. Two important decisions a practitioner must make regarding incorporating trees into an agricultural operation concern are spacing and timing of tree growth. First, trees can be grown in zones or scattered across the land. Zones can be in lines, plots, blocks, or any other systematic arrangement on the land. Spacing between trees is a powerful management tool in both zoned and scattered arrangements because it determines the level and intensity of competition and facilitates management. If the trees are growing too close together, growth may be reduced as a result of competition for moisture and nutrients, as well as issues related to crop planting, fertilizing, and harvesting by machinery.

Second, timing can influence competition between trees and crops and labor costs for planting and harvesting. If trees and crops are grown sequentially, direct competition between the two groups of plants can be greatly reduced. However, staggering the land-management techniques may increase the required labor and associated costs. If trees and crops are grown simultaneously, then direct competition between the two groups of plants may be increased, but labor costs may be reduced because of the combined management.

Adding Crops and Livestock to Silviculture. As with adding trees to establish agriculture, the same issues of spacing and timing exist when adding crops to a forest. With the application of agroforestry techniques to land under more forest-focused management, the overall goals shift from long-term forest management to include short-term crop rotations. One different strategy of adding crops to silviculture is called taungya, a Burmese term for growing crops during the first few years of tree-plantation establishment. The goal of taungya is to gain short-term crop benefits during the early stages of tree establishment. After one to three years, the crops are no longer sown, and the focus is turned to the management of the trees. Whether cropping ends after a few years or is continued indefinitely, there is a need to space trees effectively so that the future plantation can successfully reach the long-term goals defined at the outset.

Applications and Products

Tree-Crop Systems. Planting trees in rows, or any spacing configuration that allows for the sowing of crops between the trees, is known as intercropping, alley-cropping, and agrosilviculture. Often, the spacing is arranged to allow modern agricultural machinery use and to limit the need for physical labor. Two main approaches exist in tree-crop systems: planting trees on cropped land and planting crops on forested land. The former typically results in planting straight rows of trees, while the latter may result in establishing tree plantations or utilizing natural forests, which may add difficulty in properly spacing trees. In either approach, there is a need for practitioners to make management decisions related to the pattern of trees on the land (zoned or scattered), spacing (between zones, between individual trees), and diversity of tree species. Crops may be temporarily sown during the establishment phase of a forest, which can add complications for multiple owners between trees and crops. Tree-crop systems are common in temperate and tropical zones and have been used for centuries in Europe and North and South America for fruit, nut, olive, and grape production.

Tree-Animal Systems. Silvopasture is the management of livestock, their forage, and trees. If a pasture has trees that are not part of the active land management, then it is not agroforestry. The application of tree-animal agroforestry may be agriculture-dominated, integrated, or forestry-dominated approach. In an agriculture-dominated approach, the focus is placed on maximizing the livestock and food-product outputs. This approach may occur when trees are planted in a pasture to provide shelter for livestock or when livestock are allowed to graze in an orchard. With an integrated approach, the focus is balanced between the management of livestock outputs and tree-product outputs. In temperate areas, such as the southeastern United States, this approach is used for the management of pine plantations with grazing for cattle. Forestry-dominated approaches place management emphasis on tree outputs and utilizing livestock to maximize those tree products. In tropical areas where tree growth can be rapid, introducing livestock may be beneficial to the trees. However, in temperate areas, tree growth may be slower. If livestock are introduced too early, there may be grazing and damage to the trees, reducing the survival and success of the tree-animal system.

Shelterbelt Systems. When planted upwind from croplands, windbreaks provide linear shelter that reduces soil erosion. These windbreaks may include mixtures of trees and shrubs. A single row of trees does not provide a solid wall of protection, so multiple rows must be planted to create a stratified, continuous canopy to block wind. To reduce excess runoff and soil erosion related to water flow, contour hedgerows are planted along contours of moderate to steep slopes and can slow water movement. Contour hedgerows can be a less costly and less time-consuming strategy for reducing water erosion than constructing terraces along a slope. Depending on strategies and goals for the trees, shelterbelts can function merely as filter strips, reducing the volume of soil erosion, or they can function as alley crops, providing mulch or tree crops mixed in with the annual row crops.

Riparian Forest Systems. Riparian forests are stands of trees adjacent to a linear, flowing body of water (a river or stream). The soils of these forests are either continuously saturated or repeatedly inundated with water. Hydrology and soil types are important in determining which trees can survive and be productive. Riparian forest systems can benefit more than just the immediate community of landowners, compared with tree-crop or tree-animal systems. Forested zones adjacent to rivers and streams can maintain water quality by filtering agricultural chemicals in runoff through infiltration and immobilization by plants and soil microbes; stabilize banks and reduce erosion by creating a soil-retaining structure with roots and coarse woody debris, thereby improving water infiltration, which reduces the quantity of runoff and the erosive energy; and reduces average and fluctuations of water temperature, maintaining fish and other aquatic-organism populations. Riparian forest systems benefit both the land adjacent to the river and adjacent land downstream.

Natural-Specialty Crop Systems. Forest farming takes advantage of the shade produced by a forest canopy to produce special, high-value, non-timber forest products. In temperate agroforestry, these products include fruits, nuts, and mushrooms as food crops; ginseng, catnip, and echinacea as herbal medicines; and ferns and flowers for decorative and ornamental uses. Often, these specialty crops are added to forests where high-value timber is being produced to diversify the economic outputs.

Careers and Course Work

Because of the combination of techniques and principles used in agroforestry, practitioners benefit from a strong educational background in both agriculture and silviculture. Specialized degree programs in agroforestry, both undergraduate and graduate, are more likely found at universities in tropical regions where agroforestry is more commonly practiced. Courses in plant and animal biology, soil and water resources, crop science, and forestry are necessary to understand the application of agroforestry techniques. In addition to the actual production side of agroforestry, a social aspect related to the communities surrounds the practice, so courses in social and economic issues related to natural resources and rural areas are beneficial.

Careers in agroforestry will most likely not have the job title of “agroforester.” Typically, a professional in the field will either be a landowner practicing agroforestry or an outside consultant assisting landowners in applying techniques. The latter may be an individual working for a government agency as a local, state, or regional forester or extension specialist or for a nongovernmental organization with a mission to assist local landowners. Within the United States Department of Agriculture, there is the National Agroforestry Center. In Canada, there is the Agroforestry Development Centre within the country's Agriculture and Agri-Food Department. Outside governmental employment, opportunities do exist with organizations such as the World Agroforestry Centre, which is headquartered in Nairobi, Kenya. Because of the scale and scope of such an organization, as well as with national-level agencies, professionals usually work as part of interdisciplinary groups. Individuals with specialized education and experience in tree, crop, animal, or social sciences can be involved with agroforestry research and applications, adding to the growth and development of the field.

Social Context and Future Prospects

Implementing agroforestry techniques has improved local villages and regions' monetary, social, and ecological economies in many tropical and temperate areas. However, to garner those benefits at the national level, there is a need to scale up the techniques and practices used in agroforestry. To expand agroforestry and its benefits, national governmental agencies and multinational nongovernment organizations must take an active role in disseminating information and support to farmers. This has been demonstrated in several countries, including Cameroon, Indonesia, and Uganda, where increasing involvement of farmers in agroforestry programs has significantly improved the quality of products and the return on farmer investments. In each case, cooperative efforts by governmental agencies, international relief organizations, and other nongovernmental organizations have expanded the application of agroforestry techniques to magnify the geographic scope of monetary, social, and ecological benefits.

Job opportunities in agroforestry are expected to grow as those in the profession increasingly work with state and local governments to mitigate the effects of climate change on the environment and create more sustainable agriculture practices. As wildfires become an increasingly serious problem, the agroforestry field will continue to work to create solutions that help reduce the spread of fires, such as new systems of aboriculture. Another damaging effect of climate change is increased flooding. Agroforestry professionals can help lessen the impacts of floods by using tree management to reduce soil saturation in areas prone to floods. Agroforestry can help landowners prepare for risks associated with a changing climate by implementing practices to reduce heat stress on livestock, reduce windspeed, and reduce greenhouse gas emissions.

Advances continued to be made in agroforestry in the twenty-first century. Methods to increase soil health, recognizing the importance of pollinators to the ecosystem, understanding the placement of roots and their relation to crop management, and exploring innovative ways to control pests are just a few areas of study in agroforestry in the 2020s. Agroforestry also began to explore tree species that were resistant to the effects of climate change, explore new markets for goods and services, and provide community education on the benefits of agroforestry. Agrogesty became increasingly aligned with the Sustainable Development Goals of the United Nations, which aimed to increase food security, promote biodiversity, and reduce poverty worldwide. In the United States, the Department of Agriculture has continued to work with states and non-governmental organizations to provide funding and education to promote agroforestry.

Bibliography

Ashton, Mark S., and Matthew J. Kelty. The Practice of Silviculture: Applied Forest Ecology. 10th ed. Hoboken: Wiley, 2017.

Chenyang, Lingxi, Andrew Currie, Hannah Darrin, and Nathan Rosenberg. "Farming with Trees: Reforming US Farm Policy to Expand Agroforestry and Mitigate Climate Change." Ecology Law Review, 9 Sept. 2021, www.ecologylawquarterly.org/print/farming-with-trees-reforming-u-s-farm-policy-to-expand-agroforestry-and-mitigate-climate-change. Accessed 1 June 2024.

Fargione, Joe, and Renée Vassilos. "$60 Million Federal Award to Advance Agroforestry as a Profitable, Climate-Smart Solution for Farmers in 29 States." The Nature Conservancy, 14 Sept. 2022, www.nature.org/en-us/newsroom/usda-agroforestry-grant-29-states. Accessed 1 June 2024.

Gordon, Andrew M., and Steven M. Newman, eds. Temperate Agroforestry Systems. 2nd ed. Wallingford, England: CAB International, 2015.

Huxley, Peter A. Tropical Agroforestry. Hoboken, N.J.: Wiley-Blackwell, 1999.

Jose, Shibu. “Agroforestry for Ecosystem Services and Environmental Benefits: An Overview.” Agroforestry Systems 76, no. 1 (May 2009): 1–10.

Shepard, Mark. Restoration Agriculture: Real-World Permaculture for Farmers. Austin: Acres USA, 2013.

“Using Agroforestry to Meet SDGS: Establishing Forest Gardens.” UNITAR, unitar.org/about/news-stories/news/using-agroforestry-meet-sdgs-establishing-forest-gardens. Accessed 1 June 2024.