Wyatt B. from Hibbard Elementary in Rexburg asks:
Why do evergreens stay green all year round?
The reason evergreens stay green all year is not simple. Evergreen trees (trees that keep their leaves year-round instead of losing them all at once) originated in cold, northern climates. In the north, the growing season (spring/summer) is very short compared to that of the south. Trees use light to make food through photosynthesis. In order to survive in the shorter growing seasons, trees needed to gather light all year long. The only way to do this was to gather light for photosynthesis in the winter. (However, trees can only photosynthesize when water is available in a useful form, so when the only available water is snow or ice, even evergreen trees are dormant. They rest until conditions are right for photosynthesis to start again.)
Evergreen needles are an adaptation (a change that allows something to survive). Botanists long ago discovered that needles are actually regular leaves that are rolled up very tightly. This shape is an adaptation that allows evergreens to conserve water (also necessary for photosynthesis). Evergreen needles also have a very waxy coating that also helps save water during summer and winter.
Try this experiment: put two cups of water on a table in the sun, leave one cup open to the air, but cover the other with plastic wrap. The sun's energy begins to evaporate the water. From which cup does the water evaporate faster? The answer to this experiment will help you to understand how the waxy covering on evergreen needles helps conserve water.
There is your answer...evergreen trees are regular trees whose leaves are rolled up and covered with wax! This way they can make food for themselves all year long (as long as water is available in a useful form), without drying out.
Thanks for asking!
Boise Community Forestry
Boise Dept. of Parks and Recreation