All over the world, agroforestry is increasingly presented as a promising form of agriculture. What exactly does it stand for?
Agroforestry combines trees with crops and/or farmed animals. Especially in times of climate change, agroforestry can play an important role. Trees cool down, store carbon and protect against drought. Besides, the use of trees also leads to additional yields for farmers. Moreover, agroforestry can stimulate biodiversity.
Standard orchards and “home gardens”
However, agroforestry is far from being a new system. The concept itself was developed at the beginning of the 20th century, but its application dates back to the ancient Romans or earlier. In temperate regions, for example, we know the standard orchards where cattle graze among the trees. Think also of the pollard willows and wooded edges that bordered fields or meadows. In the humid tropics, agroforestry takes the form of home gardens: a combination of perennial and annual crops, close to the houses. The home gardens have at least three levels: tall trees (about 20 m) for fruit, wood, shade or feed; smaller trees such as banana or coffee trees; and finally legumes, tubers and grasses that grow up to 1.5 m high. Unfortunately, the industrialisation of agriculture from the 1950s onwards led to the gradual disappearance of trees and shrubs from agriculture.
In the humid tropics, agroforestry takes the form of home gardens: a combination of perennial and annual crops, close to the houses.
An ingenious concept
In the “modern” concept of agroforestry, the trees are planted very carefully, often in rows, but possibly also dispersed. The density is important: about 50-100 trees per hectare and 25-50 m apart. Such a density leaves enough space to use agricultural machinery. Possible negative interactions between tree and crop should also be avoided. For example, walnut and eucalyptus can hinder the growth of some crops. Competition for water can also occur. In temperate regions, farmers can prevent this by sowing a winter crop that quickly dries out the upper soil layers in spring. This forces the trees to root deeper.
In order to earn extra income, the farmer obviously has to choose trees yielding a useful by-product: wood, but also fruit, feed for cattle, honey, medicinal applications etc. In temperate regions, for example, walnuts, apples, pears, maples and sweet cherries are very suitable. These can be combined with both annual crops (cereals, protein crops, vegetables) and perennial crops (asparagus, berries, grazing pasture, etc.).
In the tropics, farmers have a much wider choice. They can opt for leguminous plants such as Faidherbia in Africa or tara in the Andean region, which add extra nitrogen to the soil, and for multipurpose trees and shrubs, with a range of applications. An example is the Moringa oleifera, a miracle tree originating from poor sandy soils at the foot of the Himalayas. The leaves and fruits of the Moringa have a very high nutritional value (proteins, iron, potassium, calcium, vitamins A and C...) and a medicinal effect against numerous diseases. The oil extracted from the seeds is similar to olive oil. Moreover, the Moringa grows quickly and is well resistant to drought.
The trees do require annual pruning, especially during the first 10 to 15 years. On the other hand, the prunings are very useful as fire wood, to bring nutrients into the soil etc.
- Anyway, if applied judiciously, agroforestry offers numerous advantages. We list the most important ones:
- With 50-100 trees per hectare - for example nuts/wheat - 1 hectare can possibly yield as much as 1.4 hectare with trees and crops separately.
- Trees grow faster than in traditional forestry because they compete less with each other. The crops themselves benefit from extra nutrients in the soil and from protection against extreme weather conditions such as wind, heavy rain, scorching heat or drought. For example, cereals appear to have a significantly higher protein content in agroforestry than in monoculture.
- The trees yield extra products (see above) and thus extra income.
- The quality wood produced reduces the pressure on tropical forests.
- The trees enhance the soil fertility. With their deep roots they extract nutrients that enrich the soil through fallen leaves, but the farmer can also apply chopped prunings to the soil.
- The trees prevent erosion: the flowing off or blowing away of fertile soil particles are not swept or blown away.
- The trees store extra carbon. In temperate regions this amounts to more than 2 tonnes/hectare/year.
- The trees attract extra biodiversity: bats, birds, earthworms... Soil life also becomes richer.
- Thanks to the increased biodiversity there are fewer diseases and pests.
- The trees provide shade for cows and other farmed animals. Chickens are calmer and healthier if they have shelter. Many trees also provide mineral-rich animal feed.
- For tourists and local residents, agroforestry land looks much more attractive than boring monocultures.
Agroforestry fact sheet (INRA)
For more information
L’agroécologie en pratiques (Agrisud)