Why Do Some Trees Keep Their Leaves All Winter?

为什么有些树整个冬天都长着叶子？

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Evergreen trees like pines and hollies retain leaves year-round thanks to special adaptations, not because they ignore seasons.

松树、冬青等常绿树全年保持叶片，靠的是特殊适应机制，而非无视季节变化。
Their needle-like or waxy-coated leaves lose water much more slowly than broad deciduous leaves do.

它们针状或蜡质涂层的叶片比宽大的落叶树叶片失水慢得多。
A thick cuticle layer and sunken stomata reduce moisture loss during cold, dry winter winds.

厚厚的角质层和下陷的气孔可减少寒冷干燥冬季大风造成的水分流失。
These leaves also contain antifreeze compounds that prevent ice crystals from rupturing their cells.

这些叶片还含有抗冻物质，防止冰晶刺破细胞。
While deciduous trees drop leaves to conserve water and energy, evergreens keep photosynthesis going—even slowly—in mild spells.

落叶树通过落叶来节约水分和能量，而常绿树即使在温和天气里也能持续（哪怕缓慢地）进行光合作用。
Older evergreen leaves gradually yellow and fall, but new ones grow steadily, maintaining green coverage.

老的常绿树叶会逐渐变黄脱落，但新叶持续生长，始终维持绿色覆盖。
This strategy works best where winters are short or soil stays unfrozen long enough for root uptake.

这种策略在冬季较短或土壤长期不冻结、根系能持续吸水的地区效果最佳。
In contrast, tropical evergreens face no frost risk, so leaf retention serves different ecological goals.

相比之下，热带常绿树无霜冻风险，其叶片保留服务于不同的生态目标。