What Is the Purpose of Winter for the Trees?
Winter can be a beautiful time of the year, especially when the snow covers the branches and piles up deep on the ground. However, for the deciduous tree, the onslaught of cold weather and long, dark nights is a time of dormancy. Woody flowering plants drop their leaves for the duration of winter, only to begin growth again with a new spring.
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Biological Clock
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Biological clocks run on both a daily and annual basis. To understand trees in winter, it is necessary to look at the process of dormancy in deciduous trees. As the fall approaches and light diminishes and temperatures drop, the tree will go into a dormant period that lasts until the spring arrives. During the winter, metabolism decreases and the leaves fall to the ground, but a low rate of metabolism is still maintained until spring. The key to dormancy seems to be the production of abscisic acid (ABA), a plant hormone, according to the Plant-Hormones website. When ABA is first produced by the plant in fall, dormancy begins. And then this condition stays with the plant all winter, as does the hormone. With the coming of spring, the acid breaks up and the plant comes out of dormancy.
Suspended Functions
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Winter makes it necessary for a perennial woody plant to cease photosynthetic activity, but even a tree without leaves will perform some basic biological functions. All summer long the tree has been making plant sugars in the green leaves and storing the energy in other parts of the plant. During the winter the plant uses the stored energy to respire and transport fluids and nutrients through the vascular system (if the sap does not freeze). When spring returns, photosynthesis starts up and the plant begins growing, producing flowers and making seeds.
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Seed Dormancy
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Even though conditions for seed germination are present in the fall, the seeds of both deciduous and coniferous plants will not germinate until the spring. To begin growth just as winter sets in would be completely detrimental to the plant. To prevent such an event from occurring, the seeds of each plant have certain conditions that need to happen before the seed will break open so the young embryo can begin a new life cycle. These conditions often include a long period of freezing.
Disease-Induced Dormancy
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A plant can go into dormancy to survive drought or an insect infestation. Again the dormant stage is triggered by production of ABA, which is produced as a reaction to plant stress, according to Kimball's Biology Pages. Many times the tree will stay dormant until the following spring and will regain health, provided the drought or disease outbreak does not continue.
Winter for Evergreens
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An evergreen, especially a conifer with needles, can still undergo photosynthesis in winter, but only in restricted amounts. Needles of conifers are specially designed to allow the exchange of gases during cold weather. This exchange combines with increased daytime respiration activity to keep a conifer alive. Evergreen conifers are the last tree left growing as you travel toward the North Pole or up the side of a large mountain.
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References
- Photo Credit winter trees image by Vladimir Gurov from Fotolia.com
