Why Do Pine Trees Stay Green?
Pine trees, like all evergreens, have evolved to cope with cold, dry climates without losing their leaves. There may only be about 115 species of pines, but they make up for it with their ubiquity and resistance to the changing seasons. This requires adaptations that other plants and trees do not have.
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Evergreens
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Pine trees are a specific genus within the division Pinophyta, or conifers, which include other cone-bearing trees such as cedars, junipers, firs, redwoods, and many others that constitute large sections of boreal forests. Because the Pinophyta is green all year round, it may be called an evergreen. Evergreen is a characteristic of plants and not a classification.
Adaptations
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The ability to gradually maintain leaves throughout the year or dispose of them entirely during the winter is an adaptation. Most plants and trees pack it in for the winter, but even the ones that keep their leaves must employ certain techniques to weather the cold climate. Tropical plants, on the other hand, always tend to keep their leaves year round.
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Deciduous Trees
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When temperatures start to drop, deciduous trees sever the tissue that connects leaves. Some pigments such as chlorophyll that collect the light for photosynthesis also begin to slowly wither. Chlorophyll predominantly reflects green light, and other pigments tend to reflect colors such as yellow and red. When chlorophyll disappears, these other pigments become much more visible, giving autumn its familiar colors.
Winter Pines
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Evergreens keep their leaves, but they still must conserve energy and water in the cold, dry climate. Pine needles have a special layer of wax that prevents water loss and dehydration. Just as some animals have antifreeze properties, evergreens also produce chemicals that prevent them from easily freezing. The long, thin needles of conifers allow snow to fall easily off the tree.
Energy and Nutrients
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The most important adaptation of an evergreen to cold climates is the response to low nutrient soil and cloudy days. Evergreens still photosynthesize throughout the winter as long as they get enough water, but the process is slowed down in order to conserve energy. Evergreens also have low nutrient loss rates because they have tissue with long life spans and low nutrient concentration.
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References
- Photo Credit snow covered pine trees image by Mike & Valerie Miller from Fotolia.com
