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原文:Desertification,the creation of desert-like conditions where none had existed before, is theresult of the vagaries of weather and climate or the mismanagement of the landor, in most cases, some combination of both. Such ecological deterioration inthe Sahel hasbeen linked in several ways to the increased size of livestock herds. Duringthe fifteen years preceding 1968, a period of extremely favorable rainfall, thepastoralists moved into the marginal regions in the north with relatively largeherds. However, with the onset of a series of dry years beginning at the end ofthe rainy season in 1967, the pastoral populations found themselves overtaxingvery marginal rangelands, with the result that the nomads viewed themselves asvictims of a natural disaster. The mistaken idea that drought is an unexpectedevent has often been used to excuse the fact that long-range planning hasfailed to take rainfall variability into account. People blame the climate foragricultural failures in semiarid regions and make it a scapegoat for faultypopulation and agricultural policies.Deterioration andultimately desertification in the Sahel and in other ecosystems can be combatedonly if an ecologically realistic carrying capacity for the rangelands isdetermined. Although there appears to be widespread agreement that such adetermination would be significant, there has been little agreement on how tomake operational the concept of carrying capacity, defined as the amount ofgrazing stock that the pasture can support without deterioration of either thepasture or the stock. Should the carrying capacity (carrying capacity:承载能力) begeared to the best, the average, or the poorest years? Which combination ofstatistical measures would be most meaningful for the planning of long-termdevelopment of rangelands? On which variables should such an assessment bebased, vegetation, rainfall, soil, ground and surface water, or managerialcapabilities? Such inconclusiveness within the scientific community, whileunderstandable, creates confusion for the land managers, who often decide totake no action or who decide that all scientific suggestions are of equalweight and, therefore, indiscriminately choose any one of those suggested.Given the downward spiral of land deterioration, it becomes essential that anecologically acceptable carrying capacity be established and enforced. Itwill also be crucial that land managers know what statistical andquasi-statistical measures actually mean: no single number can adequatelydescribe the climate regime of an arid or semiarid region. Land managers mustsupplement such terms as the “mean” with more informative statistical measuresto characterize adequately the variability of the climate. The understanding ofthis high degree of variability will serve to remove one of the major obstaclesto resolving the perennial problems of the Sahel and of other arid or semiaridregions.
3. It can be inferred from the passage thatthe nomadic tribes who moved into the marginal regions of the Sahel did NOT (A) enlarge thesize of their livestock herds (B) conserve water after the drought began
(C) live in theSahel after 1968 (D) expect adrastic change in weather conditions(D) (E)seek governmental aid in overcoming drought conditions
这题选项B和E文章哪里有提到了?我一直木有找出来~~ |
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