By Elinor Ruark
University of Georgia
"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.
NextThe 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.)