Site Selection, Survey and Treatment Plan - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 68

Fig. 3.8 Mulch-lines on
active sand dunes

percolate down and improve sub-soil water regime. Stopdams and embankments are
structures of choice for this purpose. Numerous structures with small height should
be preferred to few structures with large storage. Such structures should be located
where the slope of the stream bed is small—usually less than 2 %.

3.8.4 Treatment of Difficult Soils

Sand dunes, saline and alkaline soils, rocky and skeletal soils, and gullied areas
are very common in arid and semiarid tropics. These areas pose special problems
in afforestation programmes. The standard soil and water conservation techniques
described in earlier chapters may have to be modified while treating such areas.
Aeolian movement of soil, waterlogging in saline lands, adverse effect of salts on
plant growth, lack of adequate soil depth, and severe erosion are some of the problems
that must be addressed while raising plantations in such areas.

3.8.4.1 Afforesting Sand Dunes

Sand dunes are distinguished by the fact that the soil keeps on moving around places
and reconfiguring the ground surface. For plants to establish their roots, movement of
soil must be checked. This is achieved by adding mulch to the soil in form of brush-
wood, partly buried in the sand and partly above the ground surface (Fig. 3.8 ). The
mulch creates an obstruction which resists movement of wind and, with it, of sand.
Mulching can be done in a variety of patterns (the geometry of the lines), with a vari-
ety of materials, and at varying densities. An appropriate design of mulching should
take all these variables into consideration, apart from that of the cost of operation.
Mulching is done using locally available brushwood material. Often desert soils
show a profuse effervescence of vegetation after the rainy season. Species of shrubs
commonly available in dunes are many, but the ones suitable for mulching—those
with strong, bushy, and woody stems and branches—are fewer. Suitable brushwood
may at times have to be transported from outside. However, it is not advisable to
bring mulching material from a very long distance as that would raise the cost of
work beyond economical limit.