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.
NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.
