Trees play an important role in the ecosystem in all terrestrials and provide a range of products and services to rural and urban people. As natural vegetation is cut for agriculture and other types of development, the benefits that trees provide are best sustained by integrating trees into the agricultural system – a practice known as agroforestry.
Farmers have practised agroforestry since ancient times. Agroforestry focuses on the wide range of trees grown on farms and other rural areas. Agroforestry is a collective name for land-use systems involving trees combined with crops and/or animals on the same unit of land. It combines
- Production of multiple outputs with the protection of the resource base;
- Places emphasis on the use of multiple indigenous trees and shrubs;
- Particularly suitable for low-input conditions and fragile environments;
- It involves the interplay of socio-cultural values more than in most other land-use systems; and
- It is structurally and functionally more complex than monoculture.
Benefits of Agroforestry
- Environment Benefits: Combining trees with food crops on cropland farms yield certain important environmental benefits, both general ecological benefits and specific on-site benefits. The general ecological benefits include:
- Reduction of pressure on the forest.
- More efficient recycling of nutrients by deep-rooted trees on the site.
- Better protection of ecological systems.
- Reduction of surface run-off, nutrient leaching and soil erosion through impending effect of tree roots and stems of these processes.
- Improvement of microclimates, such as lowering of soil surface temperature and reduction of the evaporation of soil moisture through a combination of mulching and shading.
- Increment in soil nutrients through addition and decomposition of litter-fall.
- Improvement of soil structure through the constant addition of organic matter from decomposed litter.
- Economic Benefits: Agroforestry systems on croplands/farmlands bring significant economic benefits to the farmer, the community, the region or the nation. Such benefits may include:
- Increment in the maintenance of outputs of food, fuelwood, fodder, fertilizer and timber;
- Reduction in the incidence of total crop failure, common to single-cropping or monoculture system; and
- Increase in levels of farm incomes due to improved and sustained productivity.
- Social Benefits: Besides the economic benefits, social benefits occur from increase in crop and tree product yields and in the sustainability of these products. These benefits include:
- Improvement in rural living standards from sustained employment and higher incomes;
- Improvement in nutrition and health due to increased quality and diversity of food outputs; and
- Stabilization and improvement of upland communities through the elimination of the need to shift sites of farm activities.
Types of Agroforestry in non-forest areas
- Farm Forestry: Farm forestry is the name given to programmes which promote commercial tree growing by farmers on their own land. It is defined as the practice of forestry in all its aspects in and the around the farms or village lands integrated with other farm operations.
- Extension Forestry: It is the practice of forestry in areas devoid of tree growth and other vegetation situated in places away from the conventional forest areas with the object of increasing the area under tree growth. It includes the following.
- Mixed forestry: It is the practice of forestry for raising fodder grass with scattered fodder trees, fruit trees and fuelwood trees on suitable wastelands, panchayat lands and village commons.
- Shelterbelts: Shelterbelt is defined as a belt of trees and or shrubs maintained for the purpose of shelter from wind, sun, snowdrift, etc.
- Linear Strip plantations: These are the plantations of fast-growing species on linear strips of land.
- Rehabilitation of Degraded forests: The degraded area under forests needs immediate attention for ecological restoration and for meeting the socio-economic needs of the communities living in and around such areas.
- Recreation Forestry: It is the practice of forestry with the object of raising flowering trees and shrubs mainly to serve as recreation forests for the urban and rural population. This type of forestry is also known as Aesthetic forestry which is defined as the practice of forestry with the object of developing or maintaining a forest of high scenic value.
Classification of Agroforestry System
According to. Nair (1987) agroforestry systems can be classified according to the following sets of criteria:
- Structural basis: Considering the composition of the components, including spatial admixture of the woody component, vertical stratification of the component mix arid temporal arrangement of the different components.
- Functional basis: This is based on the major function or role of the different components of the system, mainly of the woody components (these can be product, e.g., production of food, fodder, fuelwood and so on or protective, e.g., windbreak, shelter-belts, soil conservation and so on).
- Socioeconomic basis: Considers the level of inputs of management (low input, high input) or intensity or scale of management and commercial goals (subsistence, commercial, intermediate).
- Ecological basis: Takes into account the environmental conditions on the assumption that certain types of systems can be more appropriate for certain ecological conditions. There may be a set of AF systems for arid and semi-arid lands etc.
Classification of Agroforestry System on Structural Basis
The structure of a system can be defined in terms of its components and the expected role or function of each. In this system the type of component and their arrangement are important. Hence, on the basis of structure, AF systems can be grouped into two categories:
- Nature of components and
- Arrangement of components.
Nature of Components : Based on the nature of components, AF systems can be classified into the following categories;
- Agrisilvicultural systems
- Silvopastoral systems
- Agrosilv opastoral systems and
- Other systems.
1. Agrisilvicultural System (crops and trees including shrubs/vines and trees)
This system involves the conscious and deliberate use of land for the concurrent production of agricultural crops including tree crops and forest crops.
Based on the nature of the components this system can be grouped into various forms.
- Improved fallow species in shifting cultivation
- The Taungya system
- Multispecies tree gardens
- Alley cropping (Hedgerow intercropping)
- Multipurpose trees and shrubs on farmlands
- Crop combinations with plantation crops ‘
- Agroforestry fuelwood production
- Soil conservation hedges etc.
- Riparian Buffer
2. Silvopastoral System (trees + pasture and/or animals)
Silvopastoral systems are definitely the most prominent agroforestry practice. Silvopastoral systems are characterized by integrating trees with forage and livestock production. Traditionally, silvopastoral systems involved grazing livestock in wooded rangeland and incorporating trees in pastures for shade and timber. The majority of rangeland grazing in hills is typically comprised the grazing of natural herbaceous and shrubby vegetation for under trees such as pines, bhimal, Oak etc. This system is again classified into three categories:
- Protein bank
- Living fence of fodder trees and hedges,
- Trees and shrubs on pasture.
3. Agrosilvopastoral System (trees + crops+pasture/animals)
This system has been grouped into two subgroups:
- Home Gardens: This is one of the oldest agroforestry practices, found extensively in high rainfall areas in tropical south and south-east Asia. Many species of trees, bushes, vegetables and other herbaceous plants are grown in dense and apparently random arrangements, although some rational control over choice plants and their spatial and temporal arrangement may be exercised. Most home gardens also support a variety of animals (cow, buffalo, bullock, goat, sheep) and birds (chicken, duck). In some places, pigs are also raised. Fodder and legumes are widely grown to meet the daily fodder requirements of cattle. The waste materials from crops and homes are used as fodder/feed for animals/birds and barn wastes are used as manure for crops.
- Woody Hedgerows: In this system, various woody hedges especially fast-growing and coppicing fodder shrubs and trees, are planted for the purpose of browse, mulch, green manure, soil conservation etc. The main aim of this system is the production of food/fodder/fuelwood and soil conservation.
4. Other Systems
The following systems can be included:
- Apiculture with Trees: In this system various honey (nectar) producing tree species frequently visited by honeybees are planted on the boundary, mixed with an agricultural crop. The main purpose of this system is the production of honey.
- Aquaforestry: In this system, various trees and shrubs preferred by fish are planted on the boundary and around fish-ponds. Tree leaves are used as forage for fish. The main or primary role of this system is fish production and bund stabilization around fish-ponds.
- Multipurpose Wood Lots: In this system special location-specific MPTS are grown mixed or separately planted for various purposes such as wood, fodder, soil protection, soil reclamation etc.
Arrangement of Components
The arrangement of components gives first priority to the plants even in AF systems involving animals. Their management according to a definite plan, say a rotational grazing scheme, gives precedence to the plants over the animals. Such plant arrangements in multispecies combinations involve the dimensions of space and time.
- Spatial Arrangement – Spatial arrangements of plants in an AF mixture may result in dense mixed stands (as in homegardens) or in sparse mix stands (as in most systems of trees in pastures). The species (or species mixtures) may be laid out in zones or strips of varying widths. There may be several forms of such zones, varying from microzonal arrangements (such as alternate rows) to macrozonal ones.
- Temporal Arrangement – Temporal arrangements of plants in AF may also take various forms. An extreme example is the conventional shifting cultivation cycles involving 2-4 years of cropping and more than 15 years of the fallow cycle, when a selected woody species or mixtures of species may be planted. Similarly, some silvopastoral systems may involve grass leys in rotation with some species of grass remaining on the land for several years. These temporal arrangements of components in AF are termed coincident, concomitant, overlapping (relay cropping), separate and interpolated.
Functional Classification of Agroforestry Systems
Two fundamental attributes of all AF systems are productivity and sustainability. This clearly indicates that AF systems have two functions.
- Productive functions (producing one or more products): The various productive functions of AF systems are:
- Other woods,
- Other products.
- Protective functions (protecting and maintaining production systems): The protective functions of AF systems are:
- Soil conservation,
- Moisture conservation,
- Soil improvement,
- Shade (for the crop, animal and man)
Socioeconomic Classification of Agroforestry Systems
Based on such socioeconomic criteria as the scale of production and level of technical input and management, agroforestry systems have been grouped into three categories:
- Intermediate and
- Subsistence systems
Ecological Grouping of Agroforestry Systems
Based on the major agroecological zones, agroforestry systems are grouped into the following categories:
- Humid/sub-humid lowlands: This region is characterized by hot humid climate for all or most of the year and evergreen or semi-evergreen vegetation. The lowland humid and subhumid tropics (commonly referred to as the humid tropics) are by far the most important ecological region in terms of the total human population. It supports extent of area and diversity of agroforestry and other land-use systems. Because of climatic conditions that favour rapid growth of a large number of plant species, various types of agroforestry plant associations can be found in areas with a high human population, e.g., various forms of home gardens, Plantation of crops with combinations and multilayer tree gardens, in areas of low population density, trees on rangelands and pastures.
- Semi-arid/arid lands: This region is characterized by rainfalls confined to 9-21 days in July -Sept., 2-4 wet months, vapour pressure deficit ranging from 9 mb in January to 30 mb in April May, solar radiation incidence (400-500 cal/cm2/day), high wind velocity (20 km/hour), high potential evapotranspiration (6 mm/day) and high mean aridity Index (70-74.8%).
- Highlands: Variable rainfall, degraded and shallow lands at high altitude to deep rich soils in valleys and great climatic variations are the features of highlands. This area is a storehouse of great biological diversity. The Himalayan region is an excellent example of this type of area. Agroforestry has long encompassed many well-known land-use systems practices.
Limitations of Agroforestry
An integrated food-tree farming system, while advantageous, does have certain negative aspects.
- Environment Aspects
- possible competition of trees with food crops for space, sunlight, moisture and nutrients which may reduce food crop yield;
- damage to food crop during tree harvest operation;
- potential of trees to serve as hosts to insect pests that are harmful to food crops; and
- rapid regeneration by prolific trees, which may displace food crops and take over entire fields.
- Socioeconomic Aspects:
- Requirement for more labour inputs, which may causes scarcity at times in other farm activities;
- Competition between food and tree crops, which could cause aggregate yields to be lower than those of a single crop;
- Longer period required for trees to grow to maturity and acquire an economic value;
- Resistance by farmers to displace food crops with trees, especially where land is scarce;
- The fact that agroforestry is more complex, less well understood and more difficult to apply, compared to single-crop farm.
Through skillful management practices, any or all of these aspects can be controlled. For example, once it is easy to adopt some or all of the following strategies:
- Select legume trees that have small or light crowns so that sufficient sunlight will reach the food crop for photosynthesis;
- Select tree species that are deep-rooted so that they will absorb moisture and nutrias from the surface layer of the soil; and
- Space the trees farther apart to reduce their competitive effects on the food crops.