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Not easy being green

The green color in plants is caused by chlorophyll (KLOR-uh-fil). This substance makes it possible for the plant to absorb, or take in, sunlight. The energy from sunlight allows the plant to create sugars, or food. This process is called photosynthesis (foe-toe-SIN-the-sis).

One advantage to staying green all year long is that the plant can keep making sugars all year. Even in the middle of winter, there are usually sunny days.

There is also a risk to keeping fragile plant parts such as leaves alive and exposed in the winter. If the winter is especially harsh, the plant could be damaged. But evergreens trade the risks for the benefits of being able to make more food.

Conifer strategies

Christmas trees are conifers (KAHN-uh-firs), or trees where the seeds are held in cones. Most conifers are evergreens. These include pines, spruces and firs.

Conifers have developed many different strategies for survival. For example, one of the oldest trees in the world is a bristlecone pine that is about 5,000 years old. This pine can shut itself down in times of stress, such as severe drought. Then, when the rains come again, it wakes up. Redwood trees are so tall that fires don’t usually reach their leaves.

Conifers grow in a kind of triangle shape. Their branches are full and wide at the bottom and thin and narrow at the top. This allows sunlight to reach needles throughout the whole tree. Top branches don’t block the sun from the bottom leaves.

Needle leaves

Conifers have leaves shaped like needles. The thin needles offer more surfaces for absorbing sunlight. Their shape allows them to hold onto water better than flat leaves. The leaves are also covered with a waxy substance that helps seal in water.

Conifers do not lose their leaves every year, so the leaves have to be tough to survive for years.

Resin

Have you ever grabbed the trunk of a Christmas tree and gotten sticky stuff all over your hands? Special cells in conifer wood produce resin (REH-zun), a sticky substance that helps protect the trees.

If the tree is hurt, resin oozes into the wound, helping it to heal. Evergreens use resin to push out insects.

This evergreen forest in North Cascades National Park in Washington is a scenic setting for a horseback ride.

Redwood trees can grow as high as 367 feet, about as high as a 35-story skyscraper. They have been growing in the California area for 20 million years.