They can cause some of the most spectacular damage attributable to earth movement or ground movement. Landslides include mudflows "mudslides"earth slumps, rockfalls, and other types of slope failures.
Farmers in many parts of the world use windbreaks - or more elaborate multi-species shelterbelts - to protect crops, water sources, soils and settlements. In addition, windbreaks are essential first steps for sand dune stabilization.
There are numerous examples that can be quoted. Tall rows of Casuarina line thousands of canals and irrigated fields in Egypt.
In Chad and Niger multi-species shelterbelts protect wide expanses of crop land from desertification. In China, there has been a massive programme in recent years to establish 'forest nets' throughout the exposed central plains region.
These consist of a grid of windbreaks, each 'net' enclosing between 4 and 26 hectares of farmland, depending on the severity of the wind problem. This includes both damage due to the loss of nutrient-rich topsoil, and damage, as a result of physical injury to crops and livestock, or the partial burial of fields.
Soils are most susceptible to wind erosion when they are dry and tare. Thus, overgrazing or any cropping activity that removes plant cover makes soils more vulnerable to wind erosion. The hazard increases with the length of time the soil surface is bare and with the degree of soil dryness.
A well-developed windbreak or shelterbelt can have a considerable influence in reducing wind velocity at the soil surface.
Where the barrier is at right angles to the wind direction, this effect has been found to extend up to times the height of the barrier to the windward side, and 30 to 35 times the height to the leeward, or down-wind side.
Small reductions in wind speed can have a significant impact on soil erosion, in part because the drying rate of the soils is reduced after rain storms. A windbreak using a mix of species provides an efficient semi-permeable barrier to wind over its full height. This produces a diverse shape to the windbreak as well as ensuring a long life of the windbreak by mixing species with varied growth rates.
In addition, a mixture of species provides risk protection against unexpected attack from diseases or insects that could destroy single species stands. Trees scattered throughout the fields such as the Acacia albida parkland savanna of West Africa can have the effect of breaking up wind patterns resulting in impacts similar to more formal windbreaks and shelterbelts.
Winds in excess of 8 metres per second, for example, can break off twigs and small limbs in orchard crops. Such losses of photosynthetic surface reduce production, and can adversely affect flowering and fruiting the following year.
Flowers on crops are particularly susceptible to high winds, and fruits may also be damaged or dislodged. The trees selected for such "salt-breaks" must have some degree of salt tolerance, for they will concentrate salt under their crowns. This is particularly important in fruit orchards Caborn Studies of the Colorado beetle, for instance, showed large reductions in populations of eggs and larvae near to windbreaks, and higher predator densities closer to the trees Karg, The effects are not uniform, however, since windbreaks can harbour harmful pest species as well as pest predators Janzen, Trees have been traditionally thought to encourage tse-tse flies, though this view is not universally accepted.
This effect may be offset, however, by the more rapid development of disease spores near to windbreaks resulting from higher relative humidity Guyot, Colorado beetle As well as reducing windspeeds, windbreaks and shelterbelts provide a range of direct benefits from the fodder, fruit, wood and other products they supply.
Even in the harsh desert environment of Yemen, a two row windbreak of Conocarpus lancifolius yielded m3 of wood per kilometre every 20 years, which was more than enough to offset the establishment costs, without considering the additional agricultural benefits Costen, Several books and manuals on the subject of windbreak design are available see Guyot, ; Bhimaya, ; Weber, Close to the windbreak, yields are reduced because of shading, root competition, and the physical space taken up by the trees.
Moving further away the benefits become more apparent, until at a certain distance they start to drop off again as the influence of the trees diminishes. Some of the most dramatic yield increases have been reported in China, where the hot, dry summer winds represent a major limitation on agricultural production.
In Hetian Prefecture, wherehectares of land were planted with Paulownia sp.
Significant increases have also been reported in a number countries with Mediterranean type climates. According to one survey covering Argentina, Bulgaria, California, Egypt, Israel, Italy, Saudi Arabia and Tunisia, well-designed windbreaks have given a net increase in crop yields of between 80 and percent Jensen, Similar increases have been reported in studies in the Antilles on vegetable yields Guyot, 1.
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Fundamental change is needed to reduce wildfire risks to people, communities and our environment and maintain Washing. Earthquakes and Safe Construction Practices The most successful way to minimize loss to life and property during earthquakes is to build disaster resistant buildings. During an earthquake the ground shakes back and forth due to the plate movement under ground.
The surface of the earth ruptures causing huge cracks; landslides occur; and sometimes tsunamis are generated during earthquakes. Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by groundwater circulating through them.
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