AGROFORESTRY SYSTEMS

Meaning of agroforestry systems

According to the European Commission Regulation 1305/2013, agroforestry is defined as that system of land use in which trees are combined with agriculture on the same tract of land. This combination leads to the creation of agroforestry systems, which involve the mixture of trees and crops, trees and pasture for livestock, and trees, crops and pasture for livestock, known as silvoarable, silvopastoral and agrosilvopastoral systems respectively. In these systems, trees are deliberately combined with crops and pasture for livestock without the intention of creating a forest. As a result, agricultural activity is not suspended.

Environmental benefits

Agroforestry systems can effectively contribute to the solution of environmental problems in arable tracts of land due to the multiple benefits derived from the synergies from the co-cultivation of trees and crops. The most important benefits are as follows (Papanastasis 2015, Dupraz et Liagre 2008):

Soil

Trees within agroforestry systems provide organic matter through their roots and foliage, resulting in the improvement of the physical and chemical properties of the soil. Specifically, soil porosity is improved and fertility is increased. Also, they affect microorganisms and favour the establishment of symbiotic mycoflora. However, their most important function is soil protection from erosion thanks to their deep root system, especially in steep areas of land (Figure 2).

Water and nutrients

Trees intercept the surface runoff of nutrients added through fertilizers and channel these into the soil, as its permeability increases at the same time. In this way, the pollution of neighboring sensitive ecosystems (e.g. wetlands, lakes, rivers) is avoided. In addition, they create a “safety net” with their deep root system, which traps nitrates leached from the root zone of crop plants and absorbs them, thus preventing groundwater pollution. Finally, trees prevent soil salinization and increase crop yield.

Biodiversity

Trees create a multitude of habitats for various species of flora and fauna, both above and below ground. When planted in rows, the zone they take up within the field becomes a refuge for many species because it is not cultivated. On the other hand, the complexity of agroforestry habitats creates conditions of competition between harmful and non-harmful organisms, resulting in the reduction of insects and diseases affecting agricultural crops.

Climate change

Trees improve air quality and the microclimate, thus enhancing agricultural production in the farms where they are established. However, their decisive contribution is carbon storage and mitigation of the effects of climate change. This is done through their significant contribution to the reduction of carbon dioxide in the atmosphere by photosynthesis, with which they release oxygen and trap carbon in their trunk, branches, roots and soil. Agroforestry has been credited as a carbon sequestration strategy since the Kyoto Protocol in 1997, because it is considered as having greater potential than other land uses, especially agriculture. According to research conducted in France, an agroforestry field can sequester and store from 1.4 to 4 tons of carbon per hectare per year with a density of 50-100 trees per hectare, an amount that is 5-10 times greater than in a field with herbaceous agricultural crop (Dupraz et Liagre 2008). This means that agroforestry systems can contribute to an increased rate of carbon sequestration thus resulting in the decrease of the carbon footprint of agriculture.

The plantation of forest or fruit trees in arable land increases their overall productivity

Establishment of agroforestry systems

Agroforestry systems can act as a solution to environmental problems faced by treeless arable lands. Their establishment should take a scientific approach, so that they are compatible with the equipment and cultivation practices already applied in these tracts of land. Establishing modern agroforestry systems requires the following steps (Papanastasis 2015):

Selection of suitable tree species

Trees to be chosen should be able to adapt to the climatic conditions of the area where they will be established and serve the intended purpose. These could be forest trees that produce timber (e.g. poplar, hackberry, lime tree), timber and fruits (e.g. walnut, chestnut), timber and fodder (e.g. carob tree) as well as timber and wind protection (e.g. cypress) or simply fruit trees, especially local varieties. It is imperative that seedlings to be planted should, as much as possible, be healthy and originating from domestic genetic material.

Choosing the right agricultural crop

Agricultural crops can be perennial or annual, as long as their biological cycles are combined with trees. For example, winter grains and legumes are grown when trees are still leafless, so competition is limited. In contrast, industrial plants growing in the summer period compete with trees for light and water unless they are irrigated (Figure 3).

Density and arrangement of trees

When trees are mature, they should not exceed 100 individuals per hectare, but it is recommended to plant more at the beginning, so that they can later be reduced by thinning. In large farms, the trees should be established in parallel lines, 25-35m apart, depending on the tree species and the machinery used by the farmer, while along the line the distances can vary from 4-10 m. In small farms, however, it is preferable to plant trees on their borders.

Tree care

Trees should be cared for regularly with proper pruning so that they form a bare trunk of 2-3 m, a height that will have high commercial value when the tree is felled. Also, the crown must also be regularly pruned so as not to overshadow the agricultural crop. In a rationally managed agroforestry system, trees cover an area equal to 15-20% of the farm’s surface, depriving it of agricultural production. Its overall productivity however is higher than when the agricultural crop is grown as a monoculture.