Agroforestry is a land use management system in which trees or shrubs are grown around or among crops or pastureland. This intentional combination of agriculture and forestry has varied benefits, including increased biodiversity and reduced erosion. Agroforestry practices have been successful in sub-Saharan Africa and in parts of the United States.
The theoretical base for agroforestry comes from ecology, via agroecology. From this perspective, agroforestry is one of the three principal agricultural land-use sciences. The other two are agriculture and forestry.
Agroforestry shares principles with intercropping. Both place two or more plant species (such as nitrogen-fixing plants) in close proximity and both provide multiple outputs. As a consequence, overall yields are higher and because a single application or input is shared, costs are reduced.
Depleted soils 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. Soil cover is a crucial factor in preventing erosion. Cleaner water through reduced nutrient and soil surface runoff can be a further advantage of agroforestry. The runoff can be reduced by decreasing its velocity and increasing infiltration into the soil. Compared to row-cropped fields nutrient uptake can be higher and reduce nutrient loss into streams.
Carbon sequestration is an important ecosystem service. 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.
Parklands are visually defined by the presence of widely scattered trees . The trees are usually of a single species with regional favorites. The trees offer shade to grazing animals, protect crops against wind bursts, provide tree prunings for firewood, and host insect or rodent-eating birds.
Research with Faidherbia albida in Zambia showed that mature trees can sustain maize yields of 4.1 tonnes per hectare compared to 1.3 tonnes per hectare without these trees. Unlike other trees, Faidherbia sheds its nitrogen-rich leaves during the rainy crop-growing season so it does not compete with the crop. The leaves regrow during the dry season and provide land cover and shade for crops.