东非的干旱周期缩短得非常显著。
The drought cycle in east Africa has been contracting sharply.
一棵橡树一旦长成，就有可能在干旱甚至火灾的小周期中存活下来。
Once an oak tree becomes established, it is likely to survive minor cycles of drought and even fire.
那片现在是沙漠的地区和所有干旱地区一样，对降雨量相对更大或更小的周期极为敏感，因此那里的动植物分布发生了巨大且迅速的变化。
The areas that are now desert were, like all arid regions, very susceptible to cycles of higher and lower levels of rainfall, resulting in major, sudden changes in distributions of plants and animals.
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