1. Shelter belt is defined as a belt of trees or shrubs maintained for the purpose of shelter from wind sum and snow faller.
2. Shelter belt is a wide range o trees, shrubs and grasses planted in rows which go right across the land at right angles to the direction or the prevailing to defect in movement to reduce wind 3.Velocity and to give general protection to cultivated area wind erosion and decreasing effect of hot winds.
Shape and Composition:
A typical shelter belt has a triangular cross section. This can be done by planting tall trees in the center, flanked on both sides, successfully on other trees, tall shrubs and then low spreading shrubs and grasses. Then there should be a systematic mixture of trees, shrubs and grasses keeping their height, shape, crown form, longitivity, and resistance to insect and usefulness in view.
Density of Width:
A certain amount of penetrability is desirable in shelter belts. It has been found from experience that though solid walls provide considerable protection immediately behind them on the lee word side the effect disappears after a short distance and there is a great fluctuation in velocity on the leeward side. But is partially penetrable shelter belt the zone of influence is very much greater and velocity curve shows a smooth slowly declining trend. Thus partially penetrable shelter belt is more effective. This penetrable is done by planting trees and shrubs adequate in their rows. The planting of shrubs should be done by 1 to 1.5 m apart and trees 2-5 m apart in rows.
The width of shelter belt depends upon climatic condition wind velocity and the soil type.
The central arid zone research institute, Jodhpur has advised data in arid zone, wind velocity not exceeds 20 km/ hr. A typical belt may consist of 3-5 rows and in the same cases 7 rows may be planted as a distance of 4 m.
The orientation of shelter belt depends upon the wind direction and velocity, particularly during the vulnerable season and shelter belt should be should oriented as early as possible at right angles to the preveling wind or to the wind or to the winds that are more damaging to the preveling time of the year. In case where winds blow from different direction shelter belt should be raised in quarlerges.
Height and Spacing:
Height of shelter belt is more important because it affects the distance to which protection will be given on the leeward side. Higher the trees forming shelter belt, the greater is the beneficial effect on leeward side.
Shelter belt protect the area up to 15 to 20 times the height or belt. In Rajasthan, taking the height of shelter belt to about 7.5m spacing recommended is two times the height i.e. 75 cm.
Choice of Species:
The choice of species to be raised in shelter belt is by the climate, soil and topography of the area. It is better to grow local species which may serve the object in view, as they can be easily established.
The selected species should be fast growing, drought resistant and unpalatable to animal. It should not be leaflets at a time where protection is required.
The following species are recommended.
Calotropica, procers, crotolonia, brubia, calligoman, polygonides, clearadendron phyomodes, cassia craicaulum, dedonae visosa, jutropha curcas, sysabenia aculeate.
Acacia jacyumental, Acacia lecucophillea, Saydora oleodes.
Acacia Arabica, a senggal, Albrizza labback, A ordirchata, Dalbergia sisso. Lannnea coronmendoice, Prospopis julifora. Progemia pinnata. Cucalyptus spp.
Advantages of Shelter Belts:
1. Moderating effect on temperature. It can increase or decrease the temperature.
2. It can increase the humidity from 1 to 50% because faster evaporation from soil and crops retained due to reduced air movement.
3. It retards the evaporation.
4. It increases the soil moisture.
5. It reduces the wind velocity and wind erosion of soil from the orchard.
6. It increases the fruit production by minimizing wind damage.