Setting the long-term strategy of improving and maintaining the land productivity, adjusting the forest composition and structure so as to improve the forest quality in Beijing.

同时还应把维护和提高地力、调整森林的组成和结构作为提高森林质量的一项长期策略；

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Shifts in forest species composition ramify through the ecosystem in many ways because tree species have different, often unique properties.

由于树种具有不同的、往往是独特的特性，森林物种组成的变化以多种方式影响着生态系统。

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Long-term effects are primarily mediated by changes in tree species composition and the consequent alterations of forest structure, productivity, and nutrient uptake.

长期影响主要是由树种组成的变化以及随之而来的森林结构、生产力和养分吸收的变化所导致的。

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