BrainStuff Classics: Why Don't Evergreen Trees Lose Their Needles?

Evergreens' needles are their leaves, so why don't they change color and drop in the fall? Learn how evergreen leaves work in this classic episode of BrainStuff, based on this article: https://home.howstuffworks.com/evergreen-trees-dont-shed.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,
I'm Lauren vogele Bomb. And this is another classic from
our archives. This one details why evergreen trees like pines
and many other conifers get to keep their green leaves
year round, seemingly thumbing their nose at seasonal changes. Hey

(00:25):
brain stuff, lourenvogel Bomb. Here, evergreen trees seem to thrive
during the colder months, steadfastly holding on to their brightly colored,
needlelike leaves as temperatures plummet, bringing welcome color and contrast
to snowy landscapes. On the other hand, the wide and
flat leaves of their deciduous counterparts transform into brilliant shades
of red, orange and gold during the chilly and dry

(00:46):
days of fall and early winter, only to eventually shed
Their branches will remain barren until spring. So why are evergreens,
which include many, but not all coniferous trees such as pines, firs, junipers,
and spruces, is immune to seasonal leaf changes in shedding,
while species of deciduous trees like aspens, birch, cherry, oak,
and maple aren't. It mostly comes down to a little

(01:10):
thing you might have learned about in biology class called photosynthesis.
Both deciduous and evergreen trees use energy from the sun
and water from the ground to turn carbon dioxide in
the air into food. The difference is that shorter days
brings less sun during the fall and winter, and that
translates into less energy. So deciduous trees bearing broad, flat

(01:32):
leaves go dormant or into a sort of hibernation mode
and shed their leaves to help them conserve water and
stay alive until spring arrives and new leaves grow from
new buds. Evergreens, meanwhile, boast needles that are actually tightly
rolled leaves, and the low surface area of this shape
helps the needles conserve water throughout the fall and winter.

(01:53):
A waxy coating on the needles also helps keep water
from evaporating. Compared with broad delicate leaves, These dense waxy
needles resist cold and stay moist, which keeps them green
throughout the winter. But evergreens actually do shed their needles,
just not all at once. As needles age, they turn
yellow brown or a reddish tan and will fall from

(02:13):
the tree, but usually only a handful at a time.
The trees are constantly growing new needles so they can
stay green year round. Evergreens greater leaf longevity means they
can survive in environments that don't work for their deciduous cousins.
In fact, evergreens can be found on every continent except Antarctica.
The bottom line is that although those colorful deciduous trees

(02:33):
attract their share of seasonal leaf peepers, trees that stay
green year round add character to people's yards during the
fall and winter, offer shelter to birds and small animals
when the winter is cold, and many species are dense
enough to serve as windbreaks and privacy screens. Today's episode

(02:54):
is based on the article why evergreen trees don't shed
their needle like leaves on HowStuffWorks dot com, written by
Windy Bellman. Brain Stuff is production of iHeartRadio in partnership
with how stuffworks dot Com and is produced by Tyler Klang.
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