Trees in the winter
Name: John H Hersey
Why do some trees in the winter lose their leaves and some
are able to keep their leaves?
You can view the leaves on a tree as its food manufacturing factory.
For some trees, especially those which live in areas which become
cold in the winter, the 'factories' do their work during the normal
growing season and are forced to 'shut-down' over the winter months.
There are many evergreens which hold their foliage all year, simply
dropping some of them periodically as they age and become less
efficient to be replaced by new needles. Larches in the area where
I live are conifers which lose their needles, which is quite rare.
You can see that foliage on a tree presents a problem: water loss
from a tree is greatest in its foliage. A tree has to 'decide'
(and this has occurred over millennia by evolution) whether to hold its
foliage or shed it. If it decides to hold the foliage, then it must
provide a means of insuring conservation of water, especially in the
winter months when dry cold winds remove water which is not easily
replace due to liquid water in the environment being frozen. Many
plant's adaptation has been the production of a waxy cuticle to
'seal-off' the leaf from the environment and reduce water loss. You
can understand that in the northern latitude's winters, sunlight
duration and intensity drops, and for some plants the best solution
has involved shedding the leaves for the winter, and growing a new
set of 'factories' in the spring.
p.s. Thanks for using NEWTON!
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Update: June 2012