Structural basis:
refers to the composition of the components, including spatial arrangement of the woody component, vertical stratification of all the components, and temporal arrangement of the different components. Hence on the basis of structure agroforestry system can be grouped into two categories.
A) Nature of components
B) Arrangement of components
A) Nature of components:
- Agrisilviculture systems/ silviagriculture/ agrosilviculture
- Silvopastoral systems/ silvipastoral
- Agrosilvopastoral systems/ agrisilvipastoral
- Other systems
I. Agrisilviculture/Silviagriculture/Agrosilviculture
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:
a) Improved fallow species in shifting cultivation
b) The Taungya system
c) Multispecies tree gardens
d) Alley cropping (Hedgrow intercropping)
e) Multipurpose trees and shrubs on farmlands
f) Crops combinations with plantation crops
g) Agroforestry for fuelwood production
h) Shelter belts
i) Wind breaks
j) Soil conservation hedges etc.
a) Improved fallow species in shifting cultivation:
Shifting cultivation:
In India it is prevalent in Assam, Meghalaya, Jharkhand, Manipur, Orissa, Nagaland, Chattisgarh, M.P., Arunanchal Pradesh, Andhra Pradesh, Mizoram, Tripura, Kerala, West Bengal, Sikkim.
It is known as ‘jhuming’ in North-east, ‘khallu / kurwa’ in Jharkhand and ‘dahiya’ or ‘podo’ in Orissa, Andhra Pradesh.
In this system, forest patch is selected and cleared felled. The herbs, shrubs and twigs and branches (slashed vegetation) are burnt .Cultivation of crops is done for a few years until soil fertility declines. The site is than abandoned (fallow period) and new patch is selected for cultivation of crops. The site is again cultivated after giving rest for few years.
Earlier the fallow cycle was of 20–30 year. However, due to increasing requirement for cultivation of land due to population pressure, fallow period has reduced from 25–30 years to 2–3 years which has broken down the resilience of ecosystem and the land is increasingly deteriorating. Thus now shifting cultivation has become source of ecological degradation, soil erosion and converting good forests into wastelands.
b) Taungya System of cultivation:
The taungya (taung = hill, ya = cultivation) is a Burmese word coined in Burma in 1850. The system was introduced to India by Brandis in 1890 and the first taungya plantations were raised in 1896 in North Bengal.
In India it started in 1896 in North Bengal. In 1890, it was introduced to Coorg in Karnataka. Regular plantation however started in North Bengal in 1911 for raising Sal plantations and in 1912, extended for raising Teak. In 1923 it was adopted in UP for
raising Sal plantations.
Types of Taungya:
1. Departmental Taungya
2. Leased Taungya
3. Village Taungya
c) Multi-species tree Gardens:
In this system of agroforestry, various kinds of tree species are grown mixed.
major function of this system is production of food, fodder and wood products for home consumption and sale.
d) Alley cropping (Hedge row intercropping):
- Alley cropping, also known as hedgerow intercropping,
- In this perennial, preferably leguminous trees or shrubs are grown simultaneously with an arable crop.
- The trees, managed as hedgerows, are grown in wide rows and the crop is planted in the interspace or ‘alley’ between the tree rows.
- During the cropping phase the trees are pruned and leaves and twigs are used as mulch on the cropped alleys in order to reduce evaporation from the soil surface, suppress weeds and/or add nutrients and organic matter to the top soil.
- The primary purpose of alley cropping is to maintain or increase crop yields by improvement of the soil and microclimate and weed control. Farmers may also obtaintree products from the hedgerows, including fuelwood, building poles, food, medicine and fodder, etc
e) Multipurpose trees and shrubs on farmlands:
- In this system various multipurpose tree species are scattered haphazardly or according to some systematic patterns on bunds.
- The major components of this system are multipurpose trees and other fruit trees and common agricultural crops.
- The primary role of this system is production of various trees products and the protective function is fencing and plot demarcation. Examples of multipurpose trees employed inagroforestry are: Leucaena leucocephala, Acacia albida, Ca ssia siamea, Casuarina equisetifolia, Azadirachta indica, Acacia senegal, Cocos nucifera, etc.
f) Crop combinations with plantation crops:
Perennial trees and shrubs such as coffee, tea, coconut and cocoa are combined into intercropping systems in numerous ways, including:
i. Integrated multistory mixture of plantation crops;
ii. Mixture of plantation crops in alternate or other crop arrangement;
iii. Shade trees for plantation crops
iv. Intercropping with agricultural crops.
Tea (Camilia sinensis) is grown under shade of A. chinensis, A. odoratissim, A. lebbek, A. procera, Acacia lenticularis, Derris robusta, Grevillea robusta, Acacia spp., Erythrina lithosperma, Indigofera tesmanii
Coffee (Coffea arabica) is grown under the shade of Erythrina lithosperma as temporary shade while, permanent shade trees include Ficus glomerata, F. nervosa, Albizia chinensis,
Black pepper (Piper nigrum) is grown with support from Erithrina indica, Garuga pinnata, Spondias, Mangifera, Gliricidia maculate and Grevillea robusta.
g) Agroforestry for fuelwood production:
- In this system, various multipurpose fuelwood/firewood species are inter-planted on or around agricultural lands.
- The protective role is to act as fencing, shelter belts and boundary demarcation.
- Tree species commonly used as fuelwood are: Acacia nilotica, Albizia lebbek, Cassia siamea, Casuarina equisetifolia, Dalbergia sissoo, Prosopis juliflora, Eucalyptus tereticornis, etc.
h) Shelterbelt:
A typical shelterbelt has a triangular cross-section which can be achieved by planting tall trees in the centre, flanked on both sides successively by shorter trees, tall shrubs and then low spreading shrubs and grasses.
Shelterbelt should be oriented as nearly as possible, at right angles to the prevailing wind In case, where winds blow from different directions, shelterbelt should be raised in quadrangles.