The colder the winter, the earlier native plants begin to grow again. With warmer winters as the climate changes, typical forest trees might start later and later - giving an advantage to shrubs and invasive trees

Warm winters let trees sleep longer

For their experiments, TUM researchers used twigs around 30 centimeters long from 36 different trees and shrubs, which they exposed to different temperature and light conditions in climate chambers. Each climate chamber experiment lasted six weeks. The twigs came from the "Weltwald" or "World Forest" near Freising, Germany, in which Bavarian state foresters have planted stands of trees from different climate regions. Credit: Photo by Julia Laube Copyright TU Muenchen.

by Staff Writers Munich, Germany (SPX) Nov 04, 2013

In the temperate zones, vegetation follows the change of the seasons. After a winter pause, plants put out new growth in spring. Research has now brought a new correlation to light: The colder the winter, the earlier native plants begin to grow again.
Since warmer winters can be expected as the climate changes, the spring development phase for typical forest trees might start later and later - giving an advantage to shrubs and invasive trees that don't depend on the cold.
In a recently published study, researchers at the Technische Universitaet Muenchen (TUM) investigated 36 tree and shrub species.
Their work delivered a surprising result, as lead author Julia Laube explains: "Contrary to previous assumptions, the increasing length of the day in spring plays no big role in the timing of budding. An ample 'cold sleep' is what plants need in order to wake up on time in the spring."
This applies above all to native tree species such as beech and oak, because they rely on resting in the cold to protect themselves from freezing by late spring frosts.
A different behavior is observed among pioneer species - including shrubs such as hazel bushes and primary settlers such as birch trees - and among species like locust and walnut that have moved in from warmer climate zones.
"These trees take the risk of starting earlier in the spring, because they are less strongly dependent on the cold periods," Laube says, "and in addition they sprout more quickly as temperatures rise."

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