Rob Wallace
Hi Reed!

Many species of trees also are capable of sensing the change in day length (even in leafless condition), and will respond once the day:night ratio surpasses a specific threshold level, which will trigger (temperature and water/nutrient availability permitting) bud break and leaf-out through the spring season. Although the temperature fluctuations might not be as extreme as with freezing and thawing, the various mechanisms for sensing of environmental cues are nonetheless present, and will establish the onset of active growth.

400 million years of terrestrial plant evolution can't be all wrong! They "know" what they're doing!

Rob