Agroforestry

Ecology

Ecology is the study of the relationship between the natural world and organisms.^[11] Ecologist examines ecosystems and tries to understand environmental patterns and their relationship among other living beings.^[12] It is a scientific discipline that encompasses many fields of study such as geography, biology, and environment.^[13] Agriculture is a form of ecological knowledge, often referred to agroecology.^[14] Agroecology refers to the management of food systems through ecological principles, understanding the landscape and integrating environmental, social, and economic dimensions.^[15] Nowadays, there is growing recognition of the urgency to shift toward agroecological principles that emphasize sustainable practices, with a focus on environmental and social well-being rather than solely crop production and profit making, aiming to create a more balanced and resilient food system.^[11][15]

Biodiversity

Agroforestry supports biodiversity in different ways. It provides a more diverse habitat than a conventional agricultural system in which the tree component creates ecological niches for a wide range of organisms both above and below ground. The life cycles and food chains associated with this diversification initiate an agroecological succession that creates functional agroecosystems that confer sustainability. Tropical bat and bird diversity, for instance, can be comparable to the diversity in natural forests.^[30] Although agroforestry systems do not provide as many floristic species as forests and do not show the same canopy height, they do provide food and nesting possibilities. A further contribution to biodiversity is that the germplasm of sensitive species can be preserved.^[31] As agroforests have no natural clear areas, habitats are more uniform. Furthermore, agroforests can serve as corridors between habitats. Agroforestry can help conserve biodiversity, positively influencing other ecosystem services.^[31]

Soil and plant growth

Depleted soil can be protected from soil erosion by groundcover plants such as naturally growing grasses in agroforestry systems. These help to stabilise the soil as they increase cover compared to short-cycle cropping systems.^[32][33] Soil cover is a crucial factor in preventing erosion.^[34][35] Cleaner water through reduced nutrient and soil surface runoff can be a further advantage of agroforestry. Trees can help reduce water runoff by decreasing water flow and evaporation and thereby allowing for increased soil infiltration.^[36] Compared to row-cropped fields nutrient uptake can be higher and reduce nutrient loss into streams.^[37][38]

Sustainability

Agroforestry systems can provide ecosystem services which can contribute to sustainable agriculture in the following ways:

• Diversification of agricultural products, such as fuelwood, medicinal plants, and multiple crops, increases income security^[39]
• Increased food security and nutrition by restored soil fertility, crop diversity and resilience to weather shocks for food crops^[39]
• Land restoration through reducing soil erosion and regulating water availability^[36]
• Possibility of reduced chemicals inputs, e.g. due to improved use of fertilizer, increased resilience against pests,^[29] and increased ground cover which reduces weeds^[40]

According to the Food and Agriculture Organization's The State of the World's Forests 2020, adopting agroforestry and sustainable production practices, restoring the productivity of degraded agricultural lands, embracing healthier diets and reducing food loss and waste are all actions that urgently need to be scaled up. Agribusinesses must meet their commitments to deforestation-free commodity chains and companies that have not made zero-deforestation commitments should do so.^[41]

Other environmental goals

Carbon sequestration is an important ecosystem service.^[42][31][43] Agroforestry practices can increase carbon stocks in soil and woody biomass.^[44] Trees in agroforestry systems, like in new forests, can recapture some of the carbon that was lost by cutting existing forests. They also provide additional food and products. The rotation age and the use of the resulting products are important factors controlling the amount of carbon sequestered. Agroforests can reduce pressure on primary forests by providing forest products.^[45]

Adaptation to climate change

Agroforestry can significantly contribute to climate change mitigation along with adaptation benefits.^[46] A case study in Kenya found that the adoption of agroforestry drove carbon storage and increased livelihoods simultaneously among small-scale farmers. In this case, maintaining the diversity of tree species, especially land use and farm size are important factors.^[47]

Poor smallholder farmers have turned to agroforestry as a means to adapt to climate change. A study from the CGIAR research program on Climate Change, Agriculture and Food Security found from a survey of over 700 households in East Africa that at least 50% of those households had begun planting trees in a change from earlier practices. The trees were planted with fruit, tea, coffee, oil, fodder and medicinal products in addition to their usual harvest. Agroforestry was one of the most widespread adaptation strategies, along with the use of improved crop varieties and intercropping.^[48]

Hillside systems

A well-studied agroforestry hillside system is the Quesungual Slash and Mulch Agroforestry System in Lempira Department, Honduras. This region was historically used for slash-and-burn subsistence agriculture. Due to heavy seasonal floods, the exposed soil was washed away, leaving infertile barren soil exposed to the dry season.^[55] Farmed hillside sites had to be abandoned after a few years and new forest was burned. The UN's FAO helped introduce a system incorporating local knowledge consisting of the following steps:^[56][57]

1. Thin and prune hillside secondary forest, leaving individual beneficial trees, especially nitrogen-fixing trees. They help reduce soil erosion, maintain soil moisture, provide shade and provide an input of nitrogen-rich organic matter in the form of litter.
2. Plant maize in rows. This is a traditional local crop.
3. Harvest from the dried plant and plant beans. The maize stalks provide an ideal structure for the climbing bean plants. Bean is a nitrogen-fixing plant and therefore helps introduce more nitrogen.
4. Pumpkins can be planted during this time. The plant's large leaves and horizontal growth provide additional shade and moisture retention. It does not compete with the beans for sunlight since the latter grow vertically on the stalks.
5. Every few seasons, rotate the crop by grazing cattle, allowing grass to grow and adding soil organic matter and nutrients (manure). The cattle prevent total reforestation by grazing around the trees.
6. Repeat.

Kuojtakiloyan

The kuojtakiloyan of Mexico is a jungle-landscaped polyculture that grows avocadoes, sweet potatoes, cinnamon, black cherries, cuajiniquil [es], citrus fruits, gourds, macadamia, mangoes, bananas and sapotes.^[58]

Kuojtakiloyan is a Masehual term that means 'useful forest' or 'forest that produces', and it is an agroforestry system developed and maintained by indigenous peoples of the Sierra Norte of the State of Puebla, Mexico. It has become a vital fountain of resources (food, medicinal herbs, fuels, floriculture, etc.) for the local population, but it is also a respectful transformation of the environment, with its biodiversity and nature conservation. The kuojtakiloyan comes directly from the ancestral Nahua and Totonaku knowledge of their natural environment.^[59]

The kuojtakiloyan is a jungle-landscaped polyculture in which avocados, sweet potatoes, cinnamon, black cherries, chalahuits, citrus fruits, gourds, macadamia, mangoes, bananas and sapotes are grown.^[59][60] In addition, a wide variety of harvested wild edible mushrooms and herbs (quelites). The jonote is planted because its fiber is useful in basketry, and also bamboo, which is fast growing, to build cabins and other structures. Concurrently to kuojtakiloyan, shade coffee is grown (café bajo sombra in Spanish; kafentaj in Masehual). Shade is essential to obtain high quality coffee.^[61] The local population has favored the proliferation of the stingless bee (pisilnekemej) by including the plants that it pollinates. From bees, they get honey, pollen, wax and propolis.^[59]

Shade crops

With shade applications, crops are purposely raised under tree canopies within the shady environment. The understory crops are shade tolerant or the overstory trees have fairly open canopies. A conspicuous example is shade-grown coffee. This practice reduces weeding costs and improves coffee quality and taste.^[62][63] In Sumatra, agroforestry systems mixing robusta coffee with durian and papaya serve as vital buffers for protected areas such as the Gunung Leuser National Park.^[64]

Alley cropping

With alley cropping, crop strips alternate with rows of closely spaced tree or hedge species. Normally, the trees are pruned before planting the crop. The cut leafy material - for example, from Alchornea cordifolia and Acioa barteri - is spread over the crop area to provide nutrients. The hedges serve as windbreaks and reduce erosion.^[65] In tropical areas of North and South America, various species of Inga such as I. edulis and I. oerstediana have been used for alley cropping.^[66] Weed control is inherent to the practice, providing mulch and shade.^[65]

Syntropic systems

Syntropic farming, syntropic agriculture or syntropic agroforestry is an organic, permaculture agroforestry system developed by Ernst Götsch in Brazil.^[67][68] Sometimes systems of this type are called successional agroforestry systems or SAFS, a broader concept originating in Latin America.^[69] The system focuses on replicating natural systems of accumulation of nutrients in ecosystems, replicating secondary succession, in order to create productive forest ecosystems that produce food, ecosystem services and other forest products.^[70]

The system relies on several processes:

• Dense planting mixing perennial and annual crops
• Rapid cutting and composting of fast growing pioneer species, to accumulate nutrients and biomass^[71]
• Creating greater water retention on the land through improving penetration of water into soil and plant water cycling

The systems were first developed in tropical Brazil, but many similar systems have been tested in temperate environments as soil and ecosystem restoration tactics.^[72]

The framework for the syntropic agroforestry is advocated for by Agenda Gotsch an organization built to promote the systems.^[73]

Syntropic systems have documented benefits including increased soil water penetration,^[74] increases to productivity on marginal land^[75] and soil temperature moderation.^[76]

Alley cropping

Alley cropping can also be used in temperate climates. Strip cropping is similar to alley cropping in that trees alternate with crops. The difference is that, with alley cropping, the trees are in single rows. With strip cropping, the trees or shrubs are planted in wide strips. The purpose can be, as with alley cropping, to provide nutrients, in leaf form, to the crop. With strip cropping, the trees can have a purely productive role, providing fruits, nuts, etc. while, at the same time, protecting nearby crops from soil erosion and harmful winds.^[27]

Forest farming

In forest farming, high-value crops are grown under a suitably-managed tree canopy. This is sometimes called multi-story cropping, or in tropical villages as home gardening. It can be practised at varying levels of intensity but always involves some degree of management; this distinguishes it from simple harvesting of wild plants from the forest.^[27]

Riparian forest buffers

Riparian buffers are strips of permanent vegetation located along or near active watercourses or in ditches where water runoff concentrates. The purpose is to keep nutrients and soil from contaminating the water.^[27]

Silvopasture

Trees can benefit fauna in a silvopasture system, where cattle, goats, or sheep browse on grasses grown under trees.^[27][80]

The dehesa or montado system of silviculture are an example of pigs and bulls being held extensively in Spain and Portugal.^[81]

Windbreaks

Windbreaks reduce wind velocity over and around crops. This increases yields through reduced drying of the crop and/or by preventing the crop from toppling in strong wind gusts.^[27]

Benefits

The UN state that the implementation of urban agroforestry systems offer a range of ecosystem services that can improve the health and resilience of urban areas. These benefits include improving environmental resilience, biodiversity, and social and cultural wellbeing.^[83]  

Implementation barriers and trade-offs

The implementation of urban agroforestry comes with a set of challenges unique to the urban setting. These barriers are often closely associated with economic (opportunity) costs and biophysical challenges.

Examples/Projects

Urban food forests are a form of urban agroforestry that mimic the natural forest ecosystem. The practice combines trees with food production and can be implemented within cities and on rooftops.^[107] Some examples of this practice can be found in Singapore where roof gardens are utilised for urban agroforestry.^[108] A particular example lies atop the skyscraper "CapitaSpring" known as the "1 Arden", the self-proclaimed world's highest food forest with over 150 varieties of herbs, plants, fruits and vegetables.^[109]

Community orchards (a prominent form of community gardens) represent further examples of urban agroforestry, as fruit and/or nut trees are planted (often in linear patterns) and managed by a community.^[110] One of these projects is the "Orchard Project", a UK charity that partners with local communities to plant, restore, and care for fruit tree orchards in urban spaces, helping people grow and harvest local food while building skills, connection, and greener, biodiverse neighbourhoods.^[111]

A city farm becomes a form of urban agroforestry when it intentionally integrates trees and perennial crops with other agricultural components in the urban landscape, thus creating a multifunctional system that produces food while also supporting ecological and community benefits.^[98] The "Stonebridge City Farm" in Nottingham was founded by residents and turned into a community city farm. The green space created is used to grow food and give the local community a place to learn, volunteer, and connect.^[112]

History

Since prehistoric times, hunter-gatherers might have influenced forests, for instance in Europe by Mesolithic people bringing favored plants like hazel with them.^[116] Forest gardens are probably the world's oldest form of land use and most resilient agroecosystem.^{[117]: 124 [118]} First Nation villages in Alaska with forest gardens filled with nuts, stone fruit, berries, and herbs, were noted by an archeologist from the Smithsonian in the 1930s.^[119]

Forest gardens are still common in the tropics and known as Kandyan forest gardens in Sri Lanka;^[120] huertos familiares, family orchards in Mexico;^[121] agroforests; or shrub gardens. They have been shown to be a significant source of income and food security for local populations.^[122]

Robert Hart adapted forest gardening for the United Kingdom's temperate climate during the 1980s.^[114]

In temperate climates

Hart began farming at Wenlock Edge in Shropshire to provide a healthy and therapeutic environment for himself and his brother Lacon. Starting as relatively conventional smallholders, Hart soon discovered that maintaining large annual vegetable beds, rearing livestock and taking care of an orchard were tasks beyond their strength. However, a small bed of perennial vegetables and herbs he planted was looking after itself with little intervention.^[123]

Following Hart's adoption of a raw vegan diet for health and personal reasons, he replaced his farm animals with plants. The three main products from a forest garden are fruit, nuts and green leafy vegetables.^[124] He created a model forest garden from a 0.12 acre (500 m²) orchard on his farm and intended naming his gardening method ecological horticulture or ecocultivation.^[117]: 45 Hart later dropped these terms once he became aware that agroforestry and forest gardens were already being used to describe similar systems in other parts of the world.^{[117]: 28, 43} He was inspired by the forest farming methods of Toyohiko Kagawa and James Sholto Douglas, and the productivity of the Keralan home gardens; as Hart explained, "From the agroforestry point of view, perhaps the world's most advanced country is the Indian state of Kerala, which boasts no fewer than three and a half million forest gardens ... As an example of the extraordinary intensity of cultivation of some forest gardens, one plot of only 0.12 hectares (0.30 acres) was found by a study group to have twenty-three young coconut palms, twelve cloves, fifty-six bananas, and forty-nine pineapples, with thirty pepper vines trained up its trees. In addition, the smallholder grew fodder for his house-cow."^{[117]: 4–5}

Seven-layer system

Projects

El Pilar on the Belize–Guatemala border features a forest garden to demonstrate traditional Maya agricultural practices.^[136][137] A further one acre model forest garden, called Känan K'aax (meaning 'well-tended garden' in Mayan), is funded by the National Geographic Society and developed at Santa Familia Primary School in Cayo.^[138]

In the United States, the largest known food forest on public land is believed to be the seven acre Beacon Food Forest in Seattle, Washington.^[139] Other forest garden projects include those at the central Rocky Mountain Permaculture Institute in Basalt, Colorado, and Montview Neighborhood farm in Northampton, Massachusetts.^[140][141] The Boston Food Forest Coalition promotes local forest gardens.^{[142][143][144][145]}

In Canada, Richard Walker has been developing and maintaining food forests in British Columbia for over 30 years. He developed a three-acre food forest that at maturity provided raw materials for a plant nursery and herbal business as well as food for his family.^[146] The Living Centre has developed various forest garden projects in Ontario.^[147]

In the United Kingdom, other than those run by the Agroforestry Research Trust (ART), projects include the Bangor Forest Garden in Gwynedd, northwest Wales.^[148] Martin Crawford from ART administers the Forest Garden Network, an informal network of people and organisations who are cultivating forest gardens.^[149][150]

Since 2014, Gisela Mir and Mark Biffen have been developing a small-scale edible forest garden in Cardedeu near Barcelona, Spain, for experimentation and demonstration.^[151]

History

Forest farming has long been practiced around the world, as people have relied on fruits, nuts, seeds, and foliage from trees and shrubs to feed themselves and their livestock.^[156]

In 1929, J. Russell Smith, emeritus Professor of Economic Geography at Columbia University, published "Tree Crops – A Permanent Agriculture" which stated that crop-yielding trees could provide useful substitutes for cereals in animal feeding programs, as well as conserve environmental health.^[157] Toyohiko Kagawa read and was heavily influenced by Smith's publication and began experimental cultivation under trees in Japan during the 1930s. Through forest farming, or three-dimensional forestry, Kagawa addressed problems of soil erosion by persuading many of Japan's upland farmers to plant fodder trees to conserve soil, supply food and feed animals. He combined extensive plantings of walnut trees, harvested the nuts and fed them to the pigs, then sold the pigs as a source of income. When the walnut trees matured, they were sold for timber and more trees were planted so that there was a continuous cycle of economic cropping that provided both short-term and long-term income to the small landowner.^[157] The success of these trials prompted similar research in other countries. World War II disrupted communication and slowed advances in forest farming.^[157] In the mid-1950s research resumed in places such as southern Africa. Kagawa was also an inspiration to Robert Hart, who pioneered forest gardening in temperate climates in the sixties in Shropshire, England.^[158]

Livestock was formerly often considered part of the forest farming system. Now animals are typically excluded and agroforestry systems that integrate trees, forages and livestock are referred to as silvopastures.^[159] Because forest farming combines the ecological stability of natural forests with productive agriculture systems, it is considered to have great potential for regenerating soils, restoring ground water supplies, controlling floods and droughts, and cultivating marginal lands.^[160]

Methods

Forest farming methods may include thinning of overstocked tree stands; integrated entries to accomplish thinning so that systemic shock is minimized; and interactive management to maintain a cross-section of healthy trees and shrubs of all ages and species. Physical disturbance to the surrounding area should be minimized.^[161]

Permaculture

Permaculture is a holistic land management system whose main purpose is to create regenerative ecosystems.^[162] There are a multitude of principles, theories and key thinkers in the field of permaculture. It is a way of land stewardship that pre-date ancient humans, and has re-gain popularity in recent years.^[162] In the 1970s, Bill Mollison and Davis Holmgren, Australian scholars, have coined the term "permaculture".^[163] The word "permaculture" derives from two key word "permanent" and "agriculture".^[1] It is a way of producing food, that incorporates ecological systems of the natural world. There are twelve principles of permaculture in Homlgren framework, which are widely used and agreed upon: (1) Observe and interact, (2) Catch and store energy, nutrients, and water (3) Obtain a yield (4) Apply self-regulation and accept feedback (5) Use and value renewable resources (6) Produce no waste (7) Design from patterns to detail (8) Integrate rather than segregate (9) Use small and slow solutions (10) Use edges and value the marginal, and (12) Creatively use and respond to change.^[163] Permaculture can be incorporated in rural or urban setting and be implemented at various scales such as small balconies to extensive acres of land.^[162] Permaculture is often understood as both a philosophy and a movement, as well as a set of agroecological principles. ^[11]