永定河沙地是北京市面积最大的风沙化土地和风沙危害最严重的地区之一，对北京市的生态环境有重要影响。

Yongding River sand land is the largest area of wind-sand land sand and is one of the most severe wind sand damage region in Beijing, Which has important influence to eco-entironment in Beijng.

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通过稳定土壤，减少水蚀和风蚀并维持土壤养分循环，林木覆盖能够防止土地退化和荒漠化。

Forests and tree cover combat land degradation and desertification by stabilizing soils, reducing water and wind erosion and maintaining nutrient cycling in soils.

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因此，每逢秋天，就在寒冷潮湿的天气来临前，他总是等待湿度达到适合的水平，风向和风速适宜才燃起他那50英亩土地的某些部份。

So each autumn, before wet, cold weather leaks over the mountains, he waits for the humidity to be just right, for the wind to blow just so, and then he burns portions of his 50-acre spread.

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