Many of nature's treasures have been buried by recent snow. Yet trees offer opportunities for exploration regardless of snow depth or season.
Tree bark has many functions, and upon close examination it varies considerably from one species to another. The variations represent different strategies for adapting to environmental conditions. Bark protects the inner tissue from insects, fire and disease, but it also provides a way to survive contrasting winter temperatures.
When the sun shines on a dark-colored tree, the bark temperature can reach about 70 degrees, even on a cold winter day. At nightfall, the contrast between that warmth and the air temperature can be dramatic, causing the bark to crack. One way to avoid frost cracks
Another adaptation is to have light-colored bark, which reflects sunlight rather than absorbing it. The paper birch and quaking aspen have white or cream-colored bark for this reason. These two species have the most northern range of any deciduous tree in our area.
Bark is more than just the skin of the tree, and there are many layers that serve distinct functions. Beneath the bark we see (technically called the outer bark) is the inner bark or phloem. The phloem transports food from the leaves to other parts of the tree.
Underneath that layer
Beneath the cambium is the xylem or sapwood, which carries nutrients from the soil through the roots and into the leaves.
Each tree has its own way of protecting these layers and the vital functions they perform. The distinct adaptations create bark variations that can help to identify the trees.
The white or paper birch has a white, papery bark that easily peels off -- but don't be tempted. The gray birch also has a white bark, but it is chalky and does not peel. All of the birches, as well as cherries and other fruit trees, have thin horizontal lines called lenticels. These are composed of small pores that allow for gas exchange between the trunk and the air.
The quaking or trembling aspen has a smooth, creamy-colored bark that may have a greenish tinge to it. The green color comes from chlorophyll, the same substance that makes leaves green. Therefore the aspen can photosynthesize through its bark, even in the winter, when there are no leaves on the tree.
The American beech also has a lighter bark. Its smooth, blue-gray bark with occasional irregular dark blotches is very distinctive. Unfortunately, it is often seen as a clean slate on which to carve initials. This obviously is not good for the tree.
Some trees, including red and sugar maple, may have smooth bark on the young trees, but as they mature the bark texture changes. Red maples develop dark gray, scaly plates as the trees age. Sugar maples have long ash-gray, flakey scales.
Though gray and brown are common colors of bark, the red oak actually has reddish furrows between the flat topped ridges that protect its trunk.
Botanists may tell you that winter tree
Looking is only one way to explore the bark. Making rubbings, especially with children, is a lot of fun and a great way to notice the differences. Put a piece of white paper against the bark and use the side of a dark-colored crayon to rub back and forth across the paper. Make note of where the tree is, and be sure to visit it again in the spring. Then you'll be able to examine the leaves, continue your exploration and deepen your acquaintance with your local trees.