Why Do Evergreens Stay Green All Year Long?
Evergreen trees are able to keep their green color year-round because of a unique set of evolved adaptations designed around their primary growing area---the cold northern regions of the world. These characteristics distinguish trees like evergreens from deciduous trees like oak or maple. Does this Spark an idea?
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Needles vs. Leaves
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Evergreens and other conifers have distinctive needles rather than leaves, though forestry expert Brian Jorgenson with the Boise, Idaho, Parks and Recreation Department says that those needles are actually deciduous leaves rolled up very tightly. According to Elizabeth Sedway, writing for examiner.com, this adaptation to needles is the tree's way of protecting its foliage all year, whereas deciduous trees are forced to shed their leaves to prevent them from freezing. Georgia Institute of Technology biology student Kevin Tuttle says that deciduous trees also shed their leaves to store the energy it would take keeping the leaves alive.
Water Conservation
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Evergreen needles are also designed to conserve water as well as energy. According to Jorgenson and Sedway, both the shape of the needles and their waxy coating---called cutin---help the tree gather and conserve water by cutting down on evaporation.
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Cold Defenses
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According to Tuttle, evergreens have developed multiple ways of feeding themselves that keep them warm. Like all plants, evergreens feed themselves through the process of photosynthesis, but only part of the time. During the coldest seasons, Tuttle says, evergreens switch to feeding off stored glucose and amino acids, which work as a sort of "antifreeze."
Constant Photosynthesis
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Photosynthesis is the process by which plants make their green lifeblood, chlorophyll. But according to Jorgenson, because the northern regions where evergreens originated have short growing seasons, trees have to gather light for photosynthesis all year long.
Needle Retention
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The constant need of evergreens to photosynthesize and gather water makes it essential that the trees hold onto their green needles as long as possible. University of California Berkeley botany student Justin Remais wrote at madsci.org that while evergreens do shed their needles, they don't lose all of them and some needles can stay on the tree in excess of four years.
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References
- Photo Credit Evergreen image by Lidka from Fotolia.com
