As the temperatures warm and days get longer, trees slowly wake back up and become active again. But as Sir Malcolm and Jane found out, even within one forest, the trees are all leafing out and growing at different rates! How do they decide when is the best time to wake up? 

 

Did you know that the colder the winter, the sooner the trees usually wake up? If the winter was mild and warm, trees tend to sleep in a bit longer in spring. How funny! It sure seems that if was warmer, they would want to start growing sooner. But it may be that trees need cold hard freezes to rest deeply and have the energy to get going. The warm spells may disrupt this rest sort of like if someone turned on your lights in the middle of the night while you were trying to sleep. Wouldn't that make it harder for you to wake up in the morning?

 

Trees all wake up for spring at different times. Young trees and shrubs closer to the forest floor usually start leafing out first, since the sunlight hits the ground and warms the air around it. So the young whippersnappers party in the sunlight before the big tall parent trees wake up and block the light. 

 

But how do trees even know it’s Spring? They don't have eyeballs or calendars or thermometers or clocks, but somehow they know! 

 

Trees can tell the temperature and amount of sunlight, and can keep track of them over time to notice changes. Beech trees have been found to need at least 13 hours of daylight before they will start growing. No one really knows exactly how trees are aware of these things, though, and it has boggled scientists for decades. We do know that leaves have light sensors, similar to receptors we have in our eyes. It may be the leaves curled in the winter buds that help the tree know when it's time to get going.

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This decision is a BIG DEAL! If trees leaf out too early, their tender new growth can be damaged by frost. If they wait too long, they miss valuable time to be soaking up the sun! Some trees are more careful and some are more bold. If you were a tree, would you risk leafing out early to have the extra fun in the sun?