Sustainable Agroforestry Systems and Practices in Agriculture

The practice of cultivating trees on farms alongside other agricultural production has a long history throughout the world. For thousands of years, people have been harvesting fruits and nuts from trees, making hay from the grass underneath or growing staple crops along the natural tree boundary that has defined their property.

People have always known that trees have their place on farms. Why? Because…

Trees bring diversity. Diversity of produce, diversity of landscape to support farming efforts and diversity of ecosystem services only trees can provide.

Trees stand for improved resistance. Resistance of farms to unpredictable weather extremes, resistance of farmers to harvest fluctuations and resistance to current and future environmental challenges.

These are important characteristics that matter especially to small farmers with limited means and land area to farm on. That is why after years of prioritizing intensive monoculture farming when trees have been removed from many lands, agroforestry practices are starting to get more recognition for the positive effects they bring.

International institutions like the United Nations Framework Convention on Climate Change (UNFCCC), the Convention on Biological Diversity (CBD) and the Food and Agriculture Organization (FAO) encourage farmers to practice agroforestry as part of their transition to sustainable agriculture of the future that will provide for their families and growing global population [1].

The role of agroforestry in sustainable agricultural systems

Agroforestry comes with many positive effects that benefit farmers and local communities, on and off-farm biodiversity, and soil health. It is a farming practice that follows the principles of agroecology and implements them through the integration of trees into the farm management. In this system, which combines the best features of agriculture and tree planting, trees have numerous important functions.

This example from a mountainous region Kyzl-Unkur in Kyrgyzstan, where traditional agroforestry practices sustain lives of subsistence farmers, demonstrates the range of valuable services trees on farms can provide.

The area has a long history of a fruitful agroforestry system which combines apple and walnut tree orchards with hay making, beekeeping and cultivation of morel mushrooms. Additional source of income for farmers comes from herbs like chamomile or St. John’s wort that can be commonly found among the trees. This farming systems supports even cattle farming, which allows farmers to obtain income from multiple sources throughout the year while sustainably managing mountainous landscape [2].

The benefits reach even beyond the boundaries of the farming community. By providing a range of products, this farming system helps to protect forests that span across surrounding mountains, as less trees need to be felled to make space for food cultivation or to provide firewood. Based on the experience of these farmers, it is undeniable that their diverse agroforestry system has positive impact on local ecology and wellbeing of people.

But what exactly makes this farming practice so promising for the sustainable future?

Agroforestry combines three important facets of sustainable agriculture while compensating for tree loss caused by increasing rates of deforestation.

It respects and supports:

• The needs of people: provides nutrient rich and diverse food for farmers, farm families, communities; helps to maintain good public health, but also improves the quality of life in rural areas;
• Profit: generates additional income for farmers and helps to provide means for rural women, empowering them and securing their livelihood;
• The planet and the environment: ecologically sound farming practices, promotes healthy biodiversity and sensible management of natural resources; agroforestry enhances soil health and improve farm’s adaptability to climate change as well as helps to mitigate the impacts [3].

By complying with these criteria, agroforestry can contribute to achieving some of the Global Goals for Sustainable Development (SDG). This includes the most important goals, such as achieving zero hunger (SDG 2), alleviating poverty (SDG 1), preventing biodiversity loss (SDG 15) and supporting the adoption of climate-smart actions (SDG 13) [1].

The ecological benefits of agroforestry

Agroforestry is an environmentally-friendly land use system where numerous interactions among trees with crops, livestock and other living organisms (incl. plants) happen.

Due to the presence of trees on farmed lands, agroforestry systems host biodiversity of native species of plants and wildlife. Numerous studies have proven that agroforestry farms feature higher biodiversity levels than other farming systems because trees create habitat for variety of birds, insects and small mammals [4]. This often includes natural predators of common crop pests, which helps to keep pest levels at check.

The presence of trees changes microclimate and alters environmental conditions for plants. Well-designed agroforestry system can suppress the growth of weeds by restricting their space and/or deterring them through the allelopathic effect–when trees release growth inhibiting chemicals into the soil [4].

The way trees change their surrounding environment should in properly designed systems lead to the suppression of weeds while encouraging crop growth due to the enhancement of favorable conditions for crop cultivation. What does this mean? For example, modification of temperature, protection from wind and more even distribution of water across the land. 

When mentioning water, we cannot forget the important role trees play in water distribution. Their presence on agricultural lands improves water infiltration and water holding capacity of soils. This increases water availability for crops and reduces surface runoff, which is a common cause of soil erosion and nutrient loss from cultivated lands. 

Agroforestry practices can have amazing effect on soils. When managed well, trees have a great capacity of maintaining soil fertility by building up organic matter, mediating nutrient cycling and preventing nutrient leaching.

In fact, trees enrich soils of nutrients. Some species like Acacia or Black Locust, even fixate atmospheric nitrogen into the soil, making it available to crops that do not have this ability.

Additionally, trees are extremely efficient at sequestering atmospheric carbon and utilizing it to form their bodies. This way, they help to offset our excessive carbon dioxide emissions and mitigate climate change.

Different types of sustainable agroforestry systems and practices

In the traditional perspective, trees were incorporated into the agricultural production to provide fruits, fodder and much needed wood to support other farming operations. It was common that trees with high productivity of either one of those goods were preserved on newly cleared agricultural lands and were included into the farm’s management.

Having trees directly on farm helped decrease farmer’s costs and even generated extra revenue, for example, apples could be used for apple juice production. Throughout the centuries and across the regions, diverse methods of utilizing trees on farms have developed. Some methods have even proven so effective that they have become the new normal in cultivation of a certain crop or a livestock species, like coffee grown in the shade of native tropical trees, which suits coffee plants better than growing alone.

Let’s have a look at the three main agroforestry systems and common practices, that have been tested through the years of humanity’s farming experience, to learn more about the advantages of each of them.

Agrisilvicultural systems—growing crops and trees together

Agrisilvicultural systems combine trees with cultivation of food crops. These do not have to be only the common cereal crops we see everywhere, it can be even shrubs, vines, mushrooms, medicinal herbs, decorative plants or fodder mixtures.

This farming system can be very diverse, ranging from specializing strictly on one tree species to one crop species which benefits from the presence of trees the best, to multilayer, multispecies plant associations on one plot.

These agrisilvicultural practices are commonly seen on farming lands across the world:

#1 Taungya

Taungya is a practice where forestry overlaps with agriculture. During the early establishment stages of forest, local farmers are allowed to grow agricultural crops among newly planted trees.

This practice is beneficial for both sides—forestry department and individual farmers. Farmers get access to land to produce crops for their livelihood and the emerging tree plantation is taken care of in the best way to ensure that young trees can develop. This reduces the costs associated with the forestry maintenance work while securing farmers’ livelihood in rural areas.  

Farmers are responsible for maintaining the plot. Their activity usually helps to keep the plot free of weeds and soils well aerated, which also encourages abundant growth of trees. In China, where this practice is commonly applied, has been observed that the survival rate of Chinese fir is five percent better and the trees grow up to 30 percent higher under this agroforestry regime [6].

The combinations of trees and crops are diverse, depending on location. For example, pine trees and poplars are interplanted with soybeans, maize or peanuts in China [6]. One plot can usually support one to three cropping seasons until the trees cast too much shade on the ground. Farmers, then, move to a new taungya plot [5].

#2 Alley cropping

Alley cropping is perhaps what most of us imagine when hearing about agroforestry. In this practice, trees are planted in rows and common crops are grown in the aisles between them. This method of growing crops is also called intercropping. One of the main advantages of intercropping is that farmers diversify their production and get annual harvest from crops, while waiting for the trees to mature and start producing as well.

An example of alley cropping system could be winter wheat or soybean intercropped with black walnut trees, which provide walnuts and fuelwood. Farmers can also plant forage crops or grass mixes among the fruit trees. This enables them to harvest grass for fodder, while getting fruits as the other stream of income (e.g. production of juices, sales of fresh fruit from farm). 

How wide the cropping plots are and what trees or crops are grown, depends solely on the farmer’s preference and species compatibility. Alley cropping allows mechanization, so farmers usually choose cropping dimensions according to the width of their machinery.

However, they still need to count with the changes that happen as trees grow bigger. Trees will eventually cast shade over most of the plot, which means that farmers need to be flexible with their choice of crops and switch to a shade resistant kind [7].

#3 Combination of plantation and crops

This agroforestry practice is as straightforward as it sounds. Perennial tree or shrub plantations are combined with other trees, or with annual cereal crops, or orchard grasses. Some sources refer to this method of farming as intercropping as well. The design and combination of individual agroforestry components depends upon the farmer’s preference and there are numerous examples of how this practice is applied for different produce throughout the world.

In some regions, farmers grow plantation crops in integrated multilayer mixture. We can see this on coffee plantations, where coffee plants are grown in the shade of banana trees because it mimics their original environment of the rainforest. According to farmers’ observation, this intercropping practice generates 50 percent more income than monocropping systems of each crop because both crops benefit from this association [8].

Another example are picturesque olive tree groves that are characteristic for the traditional Mediterranean agriculture. Olive groves often host other crop species as well. This can be grape vines, cereal crops like wheat and barley, or leguminous forage crops for livestock. In some cases, olive trees can share the same plot with other fruit trees that are either scattered among the olives or organized in a spatial arrangement that suits the farmer [9].

#4 Shelterbelts & windbreaks

Windbreaks or shelterbelts can be found on the farm’s boundaries or along the field edges. Trees or hedges are usually planted in one or multiple rows to protect crops, livestock, or farm buildings from wind.

Despite the name, protection from wind is not their only purpose. Trees planted as a physical barrier also prevent soil erosion from the land, nutrient leaching into the environment and interrupt pest infestations.

Besides defining the crop field boundaries, shelterbelts planted along animal barns have been effective in mitigating unwanted smell from spreading into the surrounding areas. You can also see tree rows or smaller shrubs planted along the roads where they help to stop snow from being blown from the agricultural fields.

More and more farmers and land managers are recognizing great benefits of incorporating windbreaks into the landscape for diversification, prevention of damage to infrastructure and creation of habitat or corridors for small wildlife.

#5 Improved fallow

Improved fallow practice is different than other agrisilvicultural practices. Trees and crops are not grown on the land simultaneously but in different time sequences. Trees or shrubs are planted during the fallow stage, when the land is left to rest for a couple years in between the main crop cultivation.

The purpose of planting trees during the fallow period is to protect soils from erosion, speed up their regeneration and enrich them of nutrients. The best trees for this purpose are leguminous trees that fix nitrogen in the soil. Their further advantage is that their leaves or fruits serve as a livestock feed, and the rest can be used for fuel or for plywood or pulpwood. Examples of nitrogen-fixing trees are Gliricidia, Leucaena or different Acacias [10].

#6 Land reclamation & conservation buffers

Trees have a wonderful ability of remediating polluted soils and regenerating degraded lands. In some areas, the presence of trees is encouraged as a vital part of the land reclamation strategy.

For example, in Germany, fast growing tree species that are also known for great phytoremediation properties, like poplars and willows, were planted in a post open pit mining reclamation site. In the early years, the biomass these trees produced was used for bioenergy. When the soils recovered in the later stage, trees were intercropped with leguminous crops to increase agricultural productivity from the land [12].

Conservation buffers serve as protective barriers, created from trees and shrubs of differing density, that mitigate the impact of farming activities on the surrounding environment.

In many land use scenarios, we can see riparian buffers covering the banks of rivers and lakes. This is because trees have irreplaceable role in preventing excessive nutrients from fertilizers and pesticide toxins from entering water and contaminating it.

According to a study from 2014, a 60 meter-wide buffer zone of trees is capable of capturing up to 99.9 percent of nitrogen and phosphorus runoff from croplands.    

#7 Forest farming

Forest farming could be described as intentional cultivation of high-value specialty crops in the native forest environment. This practice fully takes advantage of the forest habitat and specific characteristics it offers. Even though, the forest is often modified (e.g. thinned) for farming purposes and managed in a way to fully integrate specialty crops with forest trees.

In a system, where trees are utilized for the long-term timber production, high value products such as ginseng, decorative ferns, shiitake mushrooms, elderflowers, maple syrup, herbs, berries and many other goods offer sufficient short-term income.

This practice is a great way for small family farmers to diversify their production and generate revenue from permanently forested areas of their land. In fact, it can be quite profitable. Shiitake mushroom farmers can earn around 15,000 USD from a 100 square foot area each year [13].

Forest farming is labor intensive, which is a reason why large-scale farmers do not prefer this option.

#8 Mixed tree gardens

In tree gardens, multiple tree species are grown together with the purpose to provide food, fuelwood and animal fodder. A part of the harvest goes to sustaining farmer’s household, the other part is for the income.

The choice of trees and their arrangement is random and usually very diverse. You can find trees and shrubs of different sizes and growth stages on one plot. The choice of species and their maintenance fully depends upon the farmer’s decision, preference and tradition.

Mixed tree gardens have been for many years cultivated In West Sumatra, Indonesia, where around two thirds of the agricultural land are managed this way. In the area where tropical rainforest once covered most of the territory, this method of mimicking the rainforest’s diversity has proven very successful.

This agroforestry practice yields variety of wild forest fruits, medicinal plants, coffee, cinnamon, nutmeg, and important spices like chilly–all of them with a minimum human intervention [11].

Silvopasture systems–livestock raised among the trees

Silvopasture is one of the oldest farming systems, which integrates trees with grazing animals on the same farming land. Animals graze on vegetation among the trees and obtain benefits from the protective and nourishing function trees offer. Animal presence in return comes with improved productivity that is advantageous for farmers, trees and even soils.

The explanation why this practice benefits all is quite simple. In natural ecosystems, animals with plants interact on many levels. Their activity encourages nutrient cycles, food and water distribution for other organisms and supports ecological processes that take place in a healthy environment.

Silvopasture allows these interactions by closely imitating diversity of the natural environment that supports animal wellbeing and ecosystem reconstruction.

Let’s have a look in detail at the most widespread silvopasture practices:

#1 Plantation combined with pasture

In this widespread land use practice livestock is introduced among long-term tree plantation. It allows maximum utilization of space and generates income from animal production while farmers wait for the harvest from trees.

Grazing animals help with the site maintenance, removing weeds, keeping vegetation at check and even suppressing pests. When managed properly in a sensible rotation scheme, livestock can greatly enrich soils of nutrients and promote diversity of pasture vegetation without much of the farmer’s interference.

For its numerous benefits, this ancient way of raising animals is popular among farmers across the world even today. There are numerous tree plantations with different purposes that are maintained this way.

For example, the U.S. and European farmers often let livestock graze among trees marketed for their high-quality wood, such as cherry or walnut. Fast growing trees, like poplars, valued for their abundant biomass production support cattle foraging for most of the year as well.

In other parts of the world, silvopasture is practiced with sheep on rubber plantations, cattle under coconut trees, geese with horses in orange plantations or ducks under plantain trees [15].

#2 Fodder & protein banks

Fodder bank is a name for a range of perennial trees or shrubs that are planted on marginal lands to supplement feed during the season when green pasture is absent. In some regions, this period comes during colder months. In other regions, it is during the period of drought.

Livestock is either allowed to roam and graze among the fodder trees, or farmers prune the trees and feed the pruning in the stable or other livestock enclosure. In any case, tree pruning from these banks cover an important part of the livestock’s requirement for woody material, which makes up to 25 percent of the diet [16].

Fodder banks are called protein banks when they consist of leguminous trees, which are a rich source of protein and minerals for livestock during the time of feed shortage. This is the reason why legumes are a preferred choice of most farmers. Some of the popular leguminous tree species are Gliricidia, Leucaena, Ficus or Acacia.

#3 Shelterwoods and woodland grazing

Free-roaming domestic animals in the woodlands nearby human settlements have been throughout the centuries one of the most common sights across the world. Did you know that pigs and chicken originally come from the forest habitat? Releasing them free in woodland areas supports their natural behavior, and their actions even help with the maintenance of the woodlot—maintaining understory vegetation, cleaning forest of pests and enhancing biodiversity.

However, timing in this practice is crucial. If animals remain for too long in one area, they may damage the ecosystem and trees. This is the reason why farmers need to have a good rotation plan that takes the advantage of seasonal abundance of vegetation and fodder provided by wood pasture.

For example, an ancient practice called Pannage involves pigs feeding on acorns and beechnuts. In the fall, when is the nut season, pigs are released freely into the oak and beech forests, but only for the duration of 60 days which provides optimum time span for sustainable forest management [18].

In southern England is a National Park called the New Forest which is valued for its high biodiversity. What makes the park unique is that it has achieved this status thanks to the traditional woodland grazing of pigs and cattle. Grazing animals remain the full custodians of the park’s ecosystem until this day [18].

#4 Living fences

In this silvopastoral system, trees or shrubs are planted along the pasture boundaries. They create a living fence that gives animals feeling of comfort and shelter, and represents a visually pleasing element in the landscape, making the pasture appear safe and neat, well separated from the rest of the farm. Living fences usually last longer and can be a great alternative to other fencing materials.  

The choice of trees is up to farmers. They may select fodder trees that can be used to enrich animals’ diet, or trees with the economic value, such as trees grown for timber, that do not need much maintenance throughout the year.

In the United States, one of the most commonly used trees for living fencing is Osage orange. This tree is known for being very durable and well suited also for shelterbelts and windbreaks. Other popular trees are black and honey locust, or a shrub rugosa rose. They yield pods and fruits that can be utilized for livestock fodder. Similarly, the foliage of willows and elders makes a great addition to animals’ diet [19].

Agrosilvopasture systems—combining crops, livestock and trees

Agrosilvopasture is a highly diverse land use system that integrates agricultural crops with livestock and trees. In some areas of the world, especially in drylands, tropical highlands and on marginal lands which are susceptible to degradation when cultivated intensively, agrosilvopasture practices deliver the best results to sustain rural populations by providing great variety of products (crops, meat, milk, nuts, fruits and wood) [20].

However, these mixed practices are popular even among farmers who focus on sustainable and conservation agriculture. This includes permaculture, biodynamic farming, regenerative agriculture and many other practices. 

#1 Woody hedgerows

In the past, woody hedgerows were used to define property boundaries and confine livestock. These days, farmers can use other means to substitute these functions, but hedgerows still offer numerous benefits for crops, people and animals.

They protect crops from wind and provide habitat for insects, pollinators and little wildlife, especially birds (including rare species like the UK’s cirl bunting) and bats. These little hedgerow residents often help to control pest populations, which protects the agricultural production. Farm’s livestock can feed from hedges and use them for shelter when needed. And for farmers’ benefit–besides already mentioned ones–hedgerows provide additional wood and harvest.    

In some countries, hedgerows represent important element of the landscape. For example, in Northern Ireland, 60 percent of the broadleaved cover is made of shrubs and trees in hedgerows [21]. In Northern Italy, trees like elms, willows and mulberries were planted in hedges for fuelwood production. Wood was harvested through the pollarding practice, when tree branches are regularly cut off and living tree trunks remain on the boundary, slowly regreening again [18].

Hedgerows have also been planted with the main purpose of soil conservation and prevention of erosion in windy regions or on hilly lands where rapid soil loss due to surface runoff may be a problem. This is the reason why they have been abundantly planted across England, Wales and Northern Ireland [21]. Commonly preferred species for the protective purposes are native trees or shrubs.

#2 Apiculture

Apiculture stands for beekeeping. Beekeeping can be easily implemented into agroforestry system, as trees provide a nice and safe habitat for bees while supplying enough pollen and nectar for their nourishment. Bee hives can be placed along the tree line, which leaves plenty of space for other agricultural production and livestock. In some countries, like India, traditional agroforestry farmers grow trees to create habitat for wild bees and encourage their presence on farms to secure extra source of income from wild bee honey.

The presence of bees in the proximity of crops and fruit trees is highly beneficial for the yield because all those crops need pollination to produce large and healthy fruit and seeds. Important crops like coffee, sunflower, avocado, oil-seed crops and legumes are dependent upon pollination. According to farmers’ observation, sunflowers had 15 to 20 percent higher yields when bee hives were present on the same land [23]. And coffee bean production in Panama has been up to 50 percent higher thanks to pollination.

Additionally, farmers can get variety of premium products from bees that do not easily expire. This isn’t only honey, but also beeswax, propolis, pollen, royal jelly or honey wine. There is also a potential for selling bee products to the cosmetic industry. Beekeeping can be highly profitable, raising farmers’ income by up to 60 percent [22].

#3 Aquaforestry & Integrated Agri-Aquaculture Systems

Aquaculture is a practice of cultivating aquatic animals (fish, molluscs, crustaceans) and plants (seaweed) for human consumption. Aquaculture systems can be easily integrated into other farming operations, which also encompass woodland management or plantation of trees along waterbody boundaries—hence, the name aquaforestry. 

The integration of these diverse systems together has multiple benefits. Aquatic animals benefit from the presence of trees because tree foliage may serve as an additional source of nutrition. Tree branches or roots underwater help to create diverse habitat for fish to thrive. On the outside, tree roots strengthen and stabilize the banks of the waterbody.

The root network also easily reaches to the water for nutrients and moisture. Nutrient rich water encourages faster tree growth, delivering better and faster harvest. This benefits farmers who want to grow trees for profit in drier areas, as their trees do not need irrigation when integrated into the aquaculture system.

For example, a traditional system of planting mulberry trees on dykes among fishponds combined with silkworm farming in China is a great practice with high productivity that is achieved through the interconnectedness of these diverse components. Silk worm feed on mulberry leaves; silkworm waste and foliage residues are fed to fish; and pond wastewater fertilizes and irrigates mulberry trees—closing the loop of a self-sustaining system [25].

There are also benefits to the aquaculture integration with other agricultural production. Crop residues from the main crops (like soybean) grown on a farm can be fed to fish as well, while the wastewater from aquaculture can be used for crop irrigation. The wastewater is often rich in nutrients and organic matter and serves as a good and cheap crop fertilizer. Additionally, accumulated sediments from aquaculture (pond mud) can be used as a cropland fertilizer, further reducing the need for synthetic substances [24].

#4 Home gardens & fruit tree orchards

Home gardens or small subsistence farms often feature trees, animals and crops or vegetable beds. These systems are often highly diverse, multidimensional and multilayered with a combination of annual and perennial plants. They provide a wide range of produce for the farmer’s use and mutually benefit each other as well.

Trees in this practice provide fruit, diversity of fodder, and timber. But their benefits reach beyond the direct production, they perform many supportive functions for crops and animals. For example, their canopy shades them from the sun, they slow down wind, their foliage enhances soil properties and water distribution. Tree presence also positively affects animals, making them feel calmer and happier, closer to their natural environment.    

Fruit tree orchards can be as diverse as home gardens are. With the exception that the production is usually focused on smaller diversity of fruit trees than home gardens. Crops can be intercropped with fruit trees and animals can be allowed to graze in certain parts of the orchard–according to the season and the needs of the farmer.

For example, cattle can greatly help in reducing pests by eating the first fallen apples on the ground. These fruits fall off the tree in June and usually contain insect larvae that would hatch and infest the rest of the apples [27]. Similarly, in the fall, after the harvest, grazing animals help once again to clean up the orchard and fertilize the ground.

#5 Multipurpose woodlots

Multipurpose woodlots are forested areas that consist of multipurpose tree species, which are planted for their fast-growing biomass, or good quality timber, fodder for livestock or soil mulch production. Some common woodlot tree species are pine trees, eucalyptus and acacia [28]. In some woodlots, farmers combine some nut and fruit trees with berry shrubs, climbing crops like beans and various herbs.

These woodlots are usually meant to support livestock production, while at the same time provide some of the additional goods like mushrooms, berries, resins, herbs, or even Christmas trees. During the early establishment stages, trees can be intercropped with cash crops to get extra profit.

Woodlots are also often used for beekeeping, allowing for the maximum utilization of space and provision of good quality bee products.