在北美西部，大多数农业活动已被速生针叶树的单一栽培所取代。
In western North America, most have been replaced by monocultures of fast-growing conifers.
结果表明，稻曲螟的危害是单一栽培稻田的2-3倍。
The damage of Chilo suppressalis was about 2-3 times of that in monoculture paddy-field.
但随着小麦栽培品种单一化导致基因大量流失，使其遗传基础日益狭窄和抗源匮乏，对其产量和品质的进一步改良起着极大的限制作用。
However, the narrow genetic basis of wheat has limited the further improvement of yield and quality, which is essential to maintain the increasing population.
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