By Elinor Ruark
University of
Georgia
You can jump-start your car when the battery dies, but trees are
on their own. And every year, some trees don’t have enough food
to start the next year’s cycle.
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“A lot of trees in Georgia won’t start this spring,” said Kim
Coder, a professor in the University of Georgia’s Warnell School
of Forest Resources.
“The tree might have died anytime since last fall,” Coder said.
“Many will have lived through the winter but don’t have enough
energy left to completely activate their life processes.
Increasing spring temperatures mean they’ll continue to dry out
and use stored food supplies until they can’t maintain their
membranes. Then it’s over.”
For other trees, the survivors, warm spring days mean it’s time
to turn on.
Warm ‘boot’
“When the soil temperature rises above 45 degrees, the roots
become more active and begin growing,” Coder said. “As days
become longer and air temperatures warmer, buds become
active.
“Signals from the buds and root tips stimulate new growth and
food transport,” he said. “Because of the ‘start’ signal from
the
buds, the aboveground portion of the tree turns on from the top
branches downward.”
Different trees do different things when they first turn on in
spring, Coder said.
Conifers and trees with distinct annual rings, called ring-
porous
trees, begin growth by establishing water channels to the buds.
Trees with annual rings that are hard to tell apart, called
diffuse porous trees, begin by establishing new food
pathways.
“Once they’re growing, all trees make both water and food
pathways,” he said.
Next
The next step of spring for trees is to expand their buds and
leaves.
“This growth is usually at night when water contents are great
enough to pump up each tree part,” Coder said. “Once the leaves
have expanded enough to catch sunlight and their light-capture
machinery is running, the leaves start to make food.”
Most of this food is used by the stem and roots, he said. But
some is stored in the wood made in the past few years. This
stored food will get the tree through the coming winter and help
it turn on next spring.
(Elinor Ruark is a publications specialist with the
University
of Georgia College of Agricultural and Environmental
Sciences.)
