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Why Do Leaves Fall Off Trees?

Why Do Leaves Fall Off Trees?

As the days grow shorter and cooler air temperatures roll in, the color of Indiana’s trees change from summer green to the brilliant fall shades of orange, yellow, red and brown. It’s fall. Soon, the leaves will fall to the ground … or will they? We answer this question with help from Highlights Kids and NPR.  
 
The simple answer is this: Leaves fall off trees so that the trees can survive the winter. 
 
But the word “fall” is a bit misleading. It implies that the trees are passive this time of year, when, in fact, they are actively “pushing” the leaves off their branches.
 
The changes in weather and daylight trigger a hormone that releases a chemical message to each leaf that it is time to prepare for winter. Over the next few weeks, abscission cells form a bumpy line at the place where the leaf stem meets the branch. And slowly, but surely, the leaf is “pushed” from the tree branch. 
 
This winterization process is a must for trees’ survival. In spring and summer, leaves convert sunlight into energy in a process we all know as photosynthesis. During that process, the trees lose a lot of water – so much water that when winter arrives, the trees are no longer able to get enough water to replace it. 
 
And so now we know. Leaves fall—or are pushed—off trees so that the tree can survive the winter and grow new leaves in the spring. 

Looking for more Never Stop Asking "Why?" questions? Catch up on all of the past "Whys" on Pinterest or on the blog!

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