Page 130 - Soil Degradation, Conservation and Remediation

118 4 Wind Erosion

4.7 Stabilization of Dunes

A dune is usually a low hill of sand built by the flow of wind or water. Dunes occur
in different forms and sizes throughout the world, from coastal and lakeshore plains
to arid desert regions. In addition to the remarkable structure and patterns, they are
habitats of a variety of life adapted to this unique environment. Most kinds of dunes
are longer on the windward side where the sand is pushed up the dune and have a
shorter slip face in the lee of the wind. Dunes are sensitive and unstable ecosystems.
Dunes need to be stabilized, and for it, every effort should be made to protect the
integrity of the natural dune ecology.
Dune stabilization involves structural and vegetative measures. Vegetative measures
are more effective to stabilize and rehabilitate the dunes. Vegetation establishment
can be done by planting native grasses, trees, shrubs, or ground covers. The most
commonly used dune grass in the USA is the American beach grass which has been
effective in the initial stabilization of moving sand. Dune grass should be planted
before the ground becomes frozen (in cold areas). Trees for dune stabilization
include red pine, white pine, and jack pine. Trees and shrubs that can be used on wet
spots of shifting sands are cottonwood, shrub willow, and dogwoods. Tree species
adapted to sand dune plantings adjacent to large lakes are cottonwood, birch, white
pine, white oak, and bigtooth aspen. In Mauritania several tree and grass species are
used with success. Prosopis juliflora has been successful and sustainable, and
Aristida pungens is planted on very mobile strip dunes. Leptadenia pyrotechnica,
Aristida pungens, and Panicum turgidum are planted in deflation zones. Other
woody species, mainly various acacias (especially Acacia raddiana and A. senegal),
Balanites aegyptiaca, Euphorbia balsamifera, and Persica salvadora, are planted in
more stable zones. Only halophytic woody and grassy species (those resistant to soil
salinity and salt spray) are able to grow on coastal dunes. These include Nitraria
retusa, Tamarix aphylla, T. senegalensis, Casuarina equisetifolia, Atriplex halimus,
A. nummularia, and Zygophyllum spp.
Dune grasses can be effectively used for dune stabilization. Grass should be
planted in a staggered or diamond pattern for maximum erosion control. Holes
should be spaced 50 cm apart in areas where wind velocities and sand movement
are high. Culm-to-culm distance should be 60 cm in areas not directly exposed to
strong wind. The holes for plants should be between 15 and 25 cm deep to prevent
the base of the stem from drying out and to prevent the entire plant from blowing
out. Sand should be firm and moist around roots, with no air pockets near the base
of the plants. Mulch should be applied between plants to protect plantings against
rain and wind. Trees can be planted in beach grass after it has controlled sand
movement, but before the grass becomes too dense. This may be done about 2 years
after planting beach grass. Spacing of trees should be 2 × 2 m.
The mulch technique which consists of covering the dune uniformly with a natural
or artificial protective cover to prevent saltation can be adopted on flat or reasonably
even surfaces. The mulch can be made of various materials, such as straw, branches,
stalks, plastic film or acrylic fiber, and mesh. Numerous studies have demonstrated
that the straw checkerboards are efficient measures of dune stabilization. Figure 4.9