Ever green to snatch sunlight
 Q: What is the proper term/word used to describe why a tree or bush stays green throughout the
year? --William D., Maryland
A: I've asked several experts this question.
Right: [Dave Hansen, U of Minnesota Extension Service] Evergreens growing in a Minnesota forest
"I am not aware of any such term," says Art Cameron, horticulturist at Michigan State University.
That's the consensus.
Evergreen leaves are simply leaves adapted to survive winter by hoarding water. They are usually
needles or scale-like leaves with a small surface area; the leaves have a thicker skin, an anti-freeze fluid
inside the leaf cells, and often a wax coating.
"Also their leaves don't respond to the environmental clues (shortening days and cooler temperatures) that tell them to go dormant," says
Dan Lineberger, horticulturist at Texas A & M University.
That's a tipoff. The trees keep on producing chlorophyll. They use the green pigment to capture the Sun's energy and convert it to
chemical energy via photosynthesis. That's why evergreens stay green. Keep in mind, evergreens live where the living isn't easy: up
mountains and far north where it's mostly winter. They don't get much sunshine and must capitalize on what they get.
"...an evergreen tree is able to be opportunistic... It can slip in a little photosynthesis anytime the weather warms up," says Cameron.
By the way, the stems of some trees, like willows, turn green in the spring even before they leaf out so photosynthesis can proceed in
the stems, says Cameron. The tree converts the Sun's energy when the weather warms up a bit, "but without 'risking' its tender young
leaves."
Why do evergreens stay green? Robert Miller forestry professor at the University of Wisconsin at Stevens Point sums it up:
"Evolution."
(Answered by April Holladay, science correspondent, November 28, 2001)
Further Surfing:
USATODAY.com, WonderQuest: Needles-winter leaves
U of Michigan: Light and plant growth
Mystery tree
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