The Iraqi geographical area composed of about 60% desert to the west and southeast parts. Also, the desertification is going to be a serious big problem with no solution in the future amid the decrease of the water resources of Euphrates river. Dust storms are among the results of desertification and the emission out of the dried banks of rivers. I have a question that may trigger a useful discussion is: which type of natural plants may lessen the dust emission from the arid and semi arid areas if we grow on the boundaries of the desert?
The effectiveness of revegetation as a screen is considered relatively low, as it only achieves about 25% reduction (WRAP, 2006). When designing a plant barrier, species selection is crucial, as they all have a distinct size, structure, flexibility and foliage density, which influences their ability to slow down the wind or capture dust (Bouvet and al., 2007; Grant, 1985; Steffens et al., 2012). Conifers such as spruce or cedar appear to be widely used (Grant and Nickling, 1998; Rosenfeld et al., 2010). These evergreen species may be preferred for their very dense foliage and the constant protection they offer throughout the year. Other types of species can be used. For example, Ferreira (2011) suggests poplars because of their growth fast, large in size and abundant foliage.
An essential aspect of the design of a plant screen is porosity. According to various studies, a porosity of 30 to 50% would provide the best wind blocking and particle retention capacities (Grant and Nickling, 1998; Zhan and Cong, 2008). The porosity of a barrier can be determined by the choice of species and the distance between each tree. The work of Loeffler et al. (1992) allow us to determine that a single conifer has a porosity very close to zero. This affirmation is especially true for spruce and cedar, while pine has a porosity closer to 10% (Ibid). Loeffler et al. (1992) also measured the effect of distance between trees on the porosity of a coniferous screen. Their results leave
believe that to achieve 30 to 50% porosity, trees should be spaced at least two meters in the case of pines and more than two meters for spruce and thuja. As for deciduous species such as poplars, with their high porosity of 60% (Ferreira, 2011), they should be separated by less than two meters to maximize their ability to slow down the wind.
Regards
Upon your answer, there is another question which concern the calculation of the total effect of the planted area of the natural plants? In other words, how do we use the friction and roighness length parameters in studying the effects of plants on the threshold wind?
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