Tree Bark

What is bark?

Bark is the outermost layer of a tree, similar to skin. Offering protection from external elements like weather, disease, and insects; bark is a tree's first line of defense. 

The woody outermost layer, or the outer bark, is the exterior that shelters the sugar, cells, and nutrients within a tree. The next layer is the inner bark, or the phloem, where most vascular functions occur. The microstructures differ from tree to tree, but for most hardwoods, the phloem cells are vertically stacked and tubelike. The tissues formed by phloem ensure sugars are able to translocate freely from the leaves to the rest of the tree body. Next to the phloem, a thin layer of cells referred to as the cambium exists. Known as the growth layer, the cambium is where new cell development occurs. During the growing season of a tree, the cambium makes new cells that will later conjoin with the phloem, or add to the current cambium. The main function of the cambium is to increase branch, trunk, and root thickness. Following the cambium, the xylem is the youngest layer of wood, created by the cambium. The xylem acts as a pipeline, conducting water and minerals throughout the tree. Storing nutrients, the xylem has the ability to transport them from roots to leaves. Old xylem that is no longer active is known as the heartwood. Often darker than the rest of the bark, the heartwood acts as a source of support for a tree. 

Tree identification

From a distance, bark looks fairly indistinguishable, but a closer look will reveal the details that determine the species. Bark varies in texture, pattern and color, all characteristics that help with identification. Common to the Midwest, the Black Walnut has a deeply ridged, diamond-shaped bark that ranges in color from dark grey to dark brown. Oppositely, the American Beech can be easily recognized by its smooth, light grey bark. Many hardwood bark develops ridges, or a rougher texture, but the Beech remains smooth throughout its lifespan. The ridges in a bark that create gaps in the outer layer are called rhytidome. 

Some trees have peeling bark, a process which occurs when the rate of growth of a tree is at a rate faster than the bark which encloses it, or when the bark is naturally thin. This growth pressure causes the outer layer to separate and peel in curls. The Paper Birch exemplifies this process well.

Adaption

The way trees adapt to their environment influences the features they possess to be protected from it. For instance, many trees have chemicals within their bark that prevent insect invasion. Oaks contain tannins, which can be toxic when consumed by insects, and animals. Oaks are most toxic in the spring when leaves and flower buds are developing and tannins are most concentrated. Birch trees have high levels of volatile oils in their bark that are commonly extracted for their aromatic properties. The oil creates a waterproof bark coating that prevents decay. These same unique characteristics, alternatively, determine the animals that inhabit them. For example, deep ridges create crevices ideal for spiders and insects to make homes. And in many cases, birds feed on these insects, finding themselves attracted to the tree, as well. This often determines where birds build nests.

The Moral

The bottom line is that some of the features we use to identify trees are some of the same features surrounding wildlife relies on. From insects and birds, to plant life that uses tree bark to reach new heights, the barks of different tree species play an integral role in not only the development of the tree, but also the tree’s habitat.

To learn more or to start the discussion about selling your timber, contact us today.