Battle of the Trees
Plants on the March

It is easy to think that plants, especially trees, don't ever migrate. Certainly, trees do not pick up their roots and crawl to another spot. However, trees and other types of plants are always changing their habitat boundaries by sprouting seeds in new places. And as climate changes, habitat does too.

For example, when the ice age created large glacial sheets that covered much of North America, the trees at the edges of the ice were spruce and other conifers. It was too cold for the broad-leaved trees, like elms and maples. When the ice melted, the climate that favored spruce trees followed the retreating ice northward. The seedlings of the spruce forests continued to grow along the retreating ice. In a sense the forest migrated and followed the ice north. Now large spruce forests are found in Canada. The milder climate south of the ice became suitable for the trees that had previously inhabited the southern part of North America--Georgia and Alabama. Seeds of these southern trees sprouted in new areas until the trees eventually became established in places like New York and Maine. We now see a much
different variety of tree species than there was 10,000 years ago.