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Name: ethel
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Question:
Why do leaves fall off of some trees in the winter?



Replies:
An interesting question, Ethel. Biologists generally try to explain behavior in terms of a response or adaptation to an environmental challenge. The challenge in this example is thought to be snowfall. The idea is that a massive accumulation of snow in a large tree canopy would lead to mechanical damage or breakage of tree limbs or the trunk. Most deciduous trees (those that lose leaves in fall) have broad flat leaves that catch snow quite well. The advantage of this type of leaf is that they also catch the sunlight well in the summer growing season, allowing efficient photosynthesis to support rapid summer growth. The leaves are not needed in the winter because cold temperatures inhibit the enzymes of photosynthesis and prevent significant growth. Another interesting question is how evergreen trees have adapted to similar environmental challenges using a different strategy. Ask me a about it if you are interested.

Brian.



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