Agroforestry or agro-sylviculture is a land use management system in which trees or shrubs are grown around or among crops or pastureland. It combines shrubs and trees in agricultural and forestry technologies to create more diverse, productive, profitable, healthy, ecologically sound, and sustainable land-use systems.
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As a science
The theoretical base for agroforestry comes from ecology, via agroecology. From this perspective, agroforestry is one of the three principal land-use sciences. The other two are agriculture and forestry.
Agroforestry has a lot in common with intercropping. Both have two or more plant species (such as nitrogen-fixing plants) in close interaction, both provide multiple outputs, as a consequence, higher overall yields and, because a single application or input is shared, costs are reduced. Beyond these, there are gains specific to agroforestry.
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Benefits
Agroforestry systems can be advantageous over conventional agricultural, and forest production methods. They can offer increased productivity, economic benefits, and more diversity in the ecological goods and services provided .(An example of this was seen in trying to conserve Milicia excelsa.)
Depending upon the application, positive impacts of agroforestry comprise different topics.
Biodiversity
Biodiversity in agroforestry systems is typically higher than in conventional agricultural systems. With two or more interacting plant species in a given land area, it creates a more complex habitat that can support a wider variety of birds, insects, and other animals. Agroforestry is important for biodiversity for different reasons. It provides more diverse habitat than a conventional agricultural system. Tropical bat and bird diversity for instance can be comparably high to the diversity in natural forests. Although agroforestry systems do not provide as many floristic species as forests and do not show the same canopy height, they still provide food and nesting possibilities. However it has to be considered, that these systems can not replace a natural forest and have to be managed wisely. A further contribution to biodiversity is that the germplasm of sensitive species can be preserved. And as there is no regular clearing like in conventional agricultural systems, habitats are more consisting. Furthermore agroforestry systems can serve as corridors between habitats, for instance forests. Agroforestry also helps to conserve biodiversity by having positive influence on other ecosystem services. Some are mentioned below.
Soil and plant growth
Depleted soils can be prevented from soil erosion due to ground cover plants such as naturally growing grasses of agroforestry systems helping to stabilise the soil as they increase soil 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 systems. The runoff can be reduced by decreasing its velocity and increasing the infiltration into the soil in an established agroforestry system. Compared to row cropped fields the uptake of nutrients can be higher and thus result in a reduction of nutrient loss into streams.
Further advantages concerning plant growth:
- Bioremediation
- Typically more drought resistant.
- Increased crop stability
Contribution to sustainable agricultural systems
- Reducing poverty through increased production of wood and other tree products for home consumption and sale
- Contributing to food security by restoring the soil fertility for food crops
- Multifunctional site use i.e. crop production and animal grazing.
- Countering global warming and the risk of hunger by increasing the number of drought-resistant trees and the subsequent production of fruits, nuts and edible oils
- Reducing deforestation and pressure on woodlands by providing farm-grown fuelwood
- Reducing or eliminating the need for toxic chemicals (insecticides, herbicides, etc.)
- Through more diverse farm outputs, improved human nutrition
- In situations where people have limited access to mainstream medicines, providing growing space for medicinal plants
Other environmental goals
The potential of carbon sequestration is discussed as an important ecosystem service. Trees in agroforestry systems, like in new forests, can regain some of the carbon that was lost by cutting existing forests but not completely replace them. However, they provide additional food and products to people. The rotation age and the use of the resulting products are important factors contributing to the amount and duration of sequestered carbon. Agroforestry systems can offset deforestation of primary forests as they reduce pressure on the latter by providing some of the products needed from a forest.
Agroforestry practices may also realize a number of other associated environmental goals, such as:
- Odour, dust, and noise reduction
- Green space and visual aesthetics
- Enhancement or maintenance of wildlife habitat
Adaptation to climate change
There is some evidence that, especially in recent years, poor smallholder farmers are turning to agroforestry as a mean to adapt to the impacts of climate change. A study from the CGIAR research program on Climate Change, Agriculture and Food Security (CCAFS) found from a survey of over 700 households in East Africa that at least 50% of those households had begun planting trees on their farms in a change from their practices 10 years ago. The trees ameliorate the effects of climate change by helping to stabilize erosion, improving water and soil quality and providing yields of fruit, tea, coffee, oil, fodder and medicinal products in addition to their usual harvest. Agroforestry was one of the most widely adopted adaptation strategies in the study, along with the use of improved crop varieties and intercropping.
Applications
Agroforestry represents a wide diversity in application and in practice. One listing includes over 50 distinct uses.[2] The 50 or so applications can be roughly classified under a few broad headings. There are visual similarities between practices in different categories. This is expected as categorization is based around the problems addressed (countering winds, high rainfall, harmful insects, etc.) and the overall economic constraints and objectives (labor and other inputs costs, yield requirements, etc.). The categories include :
- Hillside systems
- Parklands
- Shade systems
- Crop-over-tree systems
- Alley cropping
- Strip cropping
- Fauna-based systems
- Boundary systems
- Taungyas
- Physical support systems
- Agroforests
- Wind break and shelterbelt
Hillside systems
A well-studied example of an agroforestry hillside system is the Quesungual Slash and Mulch Agroforestry System (QSMAS) in the Lempira Department, Honduras. This region in Honduras has historically been used for slash and burn subsistence agriculture. Due to heavy seasonal floods, the exposed soil was washed away, leaving the now infertile barren soil exposed to the arid drought season. Farmed hillside sites had to be abandoned after several years and new forest was burned. As an alternative to this unsustainable system, the FAO helped introduce a system incorporating local knowledge consisting of the following steps:
- Hillside secondary forest is thinned and pruned, ensuring that individual specific beneficial trees, especially nitrogen-fixing trees are left. They help reduce soil erosion, maintain soil moisture, provide shade and an input of nitrogen-rich organic matter in the form of litter.
- Maize is planted in rows and left to grow. This is a traditional plant to Honduras which local farmer have a lot of previous knowledge about.
- Maize is harvested from the dried plant and beans are simultaneously planted. The dead remaining maize stalks provide an ideal structure for the climbing bean plants. Bean is a nitrogen-fixing plant and therefore helps introduce more nitrogen to the system.
- Pumpkin can also be planted during this time, its large leaves and horizontal growth providing additional shade and moisture retention for the soil. It does not compete with the beans for sunlight since these grow vertically on the maize stalks.
- Every few seasons, the crop rotation is fulfilled by allowing cattle to graze in these areas, allowing grass to grow and the build-up of soil organic matter and nutrients in the soil. The cattle prevent total reforestation of the light agroforestry system by grazing around the individual trees and bring additional nutrients through their manure.
- Maize is grown again and the cycle is repeated. Thus, the same location can be used for long-term agriculture, helping to reduce the pressure on natural forest ecosystems and preventing land-use change with high carbon losses.
Parkland
Parklands are visually defined by the presence of trees widely scattered over a large agricultural plot or pasture. The trees are usually of a single species with clear regional favorites. Among the beaks and benefits, the trees offer shade to grazing animals, protect crops against strong wind bursts, provide tree prunings for firewood, and are a roost for insect or rodent-eating birds.
There are other gains. 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 for light, nutrients and water. The leaves then regrow during the dry season and provide land cover and shade for crops.
Shade systems
With shade applications, crops are purposely raised under tree canopies and within the resulting shady environment. For most uses, 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 the quality and taste of the coffee. Just because plants are grown under shade does not necessarily translate into lost or reduced yields. This is because the efficiency of photosynthesis drops off with increasing light intensity, and the rate of photosynthesis hardly increases once the light intensity is over about one tenth that of direct overhead sun. This means that plants under trees can still grow well even though they get less light. By having more than one level of vegetation, it is possible to get more photosynthesis, and overall yields, than with a single canopy layer.
Crop-over-tree systems
Not commonly encountered, crop-over-tree systems employ woody perennials in the role of a cover crop. For this, small shrubs or trees pruned to near ground level are utilized. The purpose, as with any cover crop, is to increase in-soil nutrients and/or to reduce soil erosion.
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 is spread over the crop area to provide nutrients for the crop. In addition to nutrients, the hedges serve as windbreaks and eliminate soil erosion.
Alley cropping has been shown to be advantageous in Africa, particularly in relation to improving maize yields in the sub-Saharan region. Use here relies upon the nitrogen fixing tree species Sesbania sesban, Euphorbia tricalii, Tephrosia vogelii, Gliricidia sepium and Faidherbia albida. In one example, a ten-year experiment in Malawi showed that, by using the fertilizer tree Gliricidia (Gliricidia sepium) on land on which no mineral fertilizer was applied, maize yields averaged 3.3 tonnes per hectare as compared to one tonne per hectare in plots without fertilizer trees nor mineral fertilizers.
In tropical areas of North and South America, various species of Inga such as Inga edulis and Inga oerstediana have been used for alley cropping.
Strip cropping
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 row. With strip cropping, the trees or shrubs are planted in wide strip. 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.
Fauna-based systems
There are situations where trees benefit fauna. The most common examples are the silvopasture where cattle, goats, or sheep browse on grasses grown under trees. In hot climates, the animals are less stressed and put on weight faster when grazing in a cooler, shaded environment. Other variations have these animals directly eating the leaves of trees or shrubs.
There are similar systems for other types of fauna. Deer and hogs gain when living and feeding in a forest ecosystem, especially when the tree forage suits their dietary needs. Another variation, aquaforestry, is where trees shade fish ponds. In many cases, the fish eat the leaves or fruit from the trees.
Boundary systems
There are a number of applications that fall under the heading of a boundary system. These include the living fences, the riparian buffer, and windbreaks.
- A living fence can be a thick hedge or fencing wire strung on living trees. In addition to restricting the movement of people and animals, living fences offer habitat to insect-eating birds and, in the case of a boundary hedge, slow soil erosion.
- 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 surface water.
- Windbreaks reduce the velocity of the winds 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.
Taungya
Taungya is a vastly used system originating in Burma. In the initial stages of an orchard or tree plantation, the trees are small and widely spaced. The free space between the newly planted trees can accommodate a seasonal crop. Instead of costly weeding, the underutilized area provides an additional output and income. More complex taungyas use the between-tree space for a series of crops. The crops become more shade resistant as the tree canopies grow and the amount of sunlight reaching the ground declines. If a plantation is thinned in the latter stages, this opens further the between-tree cropping opportunities.
Physical support systems
In the long history of agriculture, trellises are comparatively recent. Before this, grapes and other vine crops were raised atop pruned trees. Variations of the physical support theme depend upon the type of vine. The advantages come through greater in-field biodiversity. In many cases, the control of weeds, diseases, and insect pests are primary motives.
Agroforests
These are widely found in the humid tropics and are referenced by different names (forest gardening, forest farming, tropical home gardens and, where short-statured trees or shrubs dominate, shrub gardens). Through a complex, diverse mix of trees, shrubs, vines, and seasonal crops, these systems achieve the ecological dynamics of a forest ecosystem. Because of their internal ecology, they tend to be less susceptible to harmful insects, plant diseases, drought, and wind damage.
Historical use
Agroforestry similar methods were historically utilized by Native Americans. California Indians would prescribe burn oak and other habitats to maintain a 'pyrodiversity collecting model'. This method allowed for greater health of trees and the habitat in general.
Challenges
Agroforestry is relevant to almost all environments and is a potential response to common problems around the globe, and agroforestry systems can be advantageous compared to conventional agriculture or forestry. Yet agroforestry is not very widespread, at least according to current but incomplete USDA surveys as of November, 2013.
As suggested by a survey of extension programs in the United States, some obstacles (ordered most critical to least critical) to agroforestry adoption include:
- Lack of developed markets for products
- Unfamiliarity with technologies
- Lack of awareness of successful agroforestry examples
- Competition between trees, crops, and animals
- Lack of financial assistance
- Lack of apparent profit potential
- Lack of demonstration sites
- Expense of additional management
- Lack of training or expertise
- Lack of knowledge about where to market products
- Lack of technical assistance
- Cannot afford adoption or start up costs, including costs of time
- Unfamiliarity with alternative marketing approaches (e.g. web)
- Unavailability of information about agroforestry
- Apparent inconvenience
- Lack of infrastructure (e.g. buildings, equipment)
- Lack of equipment
- Insufficient land
- Lack of seed/seedling sources
- Lack of scientific research
Some solutions to these obstacles have already been suggested although many depend on particular circumstances which vary from one location to the next.
Source of the article : Wikipedia
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