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Then, after a few months, the days begin to shorten again
几个月后，白昼又开始缩短，
and the trees must shut down and shed their leaves in preparation for the cold dark time ahead.
树木开始减缓代谢，树叶开始凋零，以准备迎接寒冬的到来。
Great tracts of North America flush red as the season progresses.
随着季节的变换，北美的大片地域万山红遍，层林尽染。
The effect is so spectacular and so extensive that it can be seen from space.
这种壮观的景象发生的地域之广，甚至可以在太空中看到。
The threat of winter frost is not the only reason for trees to shed leaves.
寒冬的威胁不是树木落叶的唯一原因。
These forests stand in the tropics.
这片森林在热带地区。
Here day length never changes, but the dry season is so severe
在这里白昼没有变化，在炎热干燥的季节，
that the trees can't afford to loose the amount of water that would evaporate from their broad leaves, so the leaves must be shed.
树木无法承受水分从叶子上的大量流失，所以必须落叶。
