leaf become trapped there, and,
without a water source, the green
color begins to fade.
So what about the vibrant
fall colors? During the growing
season, leaves are actively taking
in CO
2
and using sunlight to
combine it with water to make
sugar and oxygen through
photosynthesis. This makes
chlorophyll, and chlorophyll, of
course, gives leaves their green
pigment. As fall approaches, and
the days get shorter, the leaves
cease producing chlorophyll and
the green color fades. The bright
colors that are revealed were
actually there all season long
but we couldn't see them as the
chlorophyll was blocking them.
The yellow-orange colors result
from carotenoids, the same pigments that color carrots, bananas,
and daffodils. The reds and purples are caused by anthocyanins,
the same molecules that give apples, plums, and grapes their
iconic hues. The browns revealed in trees such as beech and oak
are tannins, the bitter-tasting waste product that is left in the
leaves (that also gives tea its color). All leaves have stored waste
products, but the coloration is often blocked by other compounds
so we don't see them until the leaf as completely died — hence
why all leaves will eventually turn brown.
Evergreens prepare for the
change in seasons in other ways.
Conifers have leaves already
modified to resist drought and
freezing temperatures in the form
of needles; but that doesn't mean
they don't shed their foliage in
the fall like a deciduous tree does.
Conifers will drop leaves every
fall, just not all of them. Typically,
conifers retain 3 to 5 years worth
of needles, meaning every fall
they will shed a layer of older
needles. I used to work at a garden
center where every fall we were
bombarded with "My pine tree is
dying!" phone calls. We would ask
if the tree was dropping needles
from the tips of the branch or
from the inside of the tree. 100
percent of the time it was from the
inside. After ensuring them this was perfectly normal, we would
take the time to inform them their pine was actually a spruce. Of
course, there are exceptions to the rule, such as the larch or the
dawn redwood, which will drop all their needles each fall. Needles
that are retained generally do not freeze in the winter, even in
extreme temps, as their resin acts as a natural antifreeze.
Beyond the foliage, trees are prepping for the cold in other
ways. Temps can drop pretty low in the winter (often to -20
degrees Fahrenheit where I live) and, remarkably, the trees survive
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SPECIAL SECTION
Snow acts as a insulator, keeping
the soil warmer than the air.
Even trees "in captivity" go through a dormant cycle.
PHOTOS
COURTESY
OF
WIKI
COMMONS
