Adelaaa

 Desert formation  沙漠的形成(3)

  Four specific activities have been indentified as major contributors to the desertification processes overcultivation, overgazing firewood gathering, and overirrigation. The cultivation of crops has expanded into progressively drier regions as population densities have grown. These regions are especially likely to have periods of severe dryness, so that crop failures are common. Since the raising of most crops necessitates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid of a plant cover and susceptible to wind and wate erosion.

  The raising if livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulverization of the soil. This is usually followed by the drying of the soil and accelerated erosion.

(* Highlight 的單字是有解說的單字，非問題。)

單字解說：

1) indentified (V.)  識別； 確定；發現

2) contributor  (N.)  捐獻者；捐助者；捐款人； 撰稿人

3) overcultivation  (N.)  過度耕種

4) overgazing 過度放牧

5) overirrigation 濫灌

6) cultivation  (N.)  教養；栽培；耕作；（關係的）培植

7) crop  (N.)   作物；收成

8)  density   (N.)   密度

9) necessitate  (V.)   使成為必需；使成為必要

10) extensive   (Adj.)   大面積的；覆蓋範圍廣的

11)　tract  (N.)  大片土地 ； （人或動物體內的）管，道，束 ； （尤指有關宗教或政治主題的）短文

12)  be devoid of sth 缺少

13) susceptible   (Adj.)   易受影響的，易受傷害的； 易受感動的，感情豐富的，多情的； （尤指想法或陳述）能被理解（或證明、解釋）的

14) livestock  (N.)   牲畜；家畜；家禽

15) dominant    (Adj.)   主要的；主導的；佔優勢的

16) consequence  (N.)   （常指不好或不利的）結果