A Tree’s First Defense: Bark

Bark

What is bark? Merriam Webster defines it as;

“the tough exterior covering of a woody root or stem;specifically : the tissues outside the cambium that include an inner layer especially of secondary phloem and an outer layer of periderm”

Interesting, but why are trees covered in it? Well, there are a few reasons. Bark acts likes skin does for humans; it protects them from harm, like disease, insects, and other animals damaging the tree. A tree’s bark also protects it from the elements, like excess heat, cold, extreme amounts of sunshine, as well as evaporation. It is the tree’s form of armour, making sure that it can withstand any bumps and bruises that the world throws at it.

Not all bark is the same for all trees though. It comes in a variety of colours, from white, grey, brown to black, and many shades in between. Some trees have smooth bark, while others have rough exteriors. There are some with thorns, and still others that shed their outer bark to help keep the tree healthy. There are as many different kinds of bark, as there are trees. Here is a brief look at the different kinds you might find.

Smooth Bark:

English: American Beech

Some trees have smooth bark due to the tropical environment they are found in. When a tree has smooth bark, it makes it harder for invasive species to attack it, like climbing vines and ivies. It also offers no footholds for invading insects, deterring attack. Smooth bark grows slower though, so it takes longer to recover from broken limbs, plus limits the overall height of the tree. Examples of trees with smooth bark include American Beech, young Trembling Aspen, European Hornbeam, European Mountain Ash (Rowan), and Witch-hazel.

Rough Bark:

Bark (Photo credit: Arenamontanus)

Many trees start out with smooth bark, that later becomes ridged, scaly, and cracked as it gets older. That is because these trees tend to grow faster, thus splitting their skin as they grow. Trees with rougher bark are better able to recover from injury quickly, are better adapted to retain moisture, and can also survive elements like forest fires better. Some barks also produce strong tannins that deter insects from eating them. Examples of trees with rough bark are older Red Oak and Red Maple, Caucasian Wingnut, Ginkgo, Hackberry, Jack Pine, and Sassafras.

Peeling or Flaky Bark:

Birch, with bark peeling (Photo credit: Martin LaBar)

Some trees shed their outer bark. This may be to deter insect infestation, or to shed lichens, mosses and other bacteria. Essentially it is the tree’s way of exfoliating to keep itself healthier. Examples of trees with peeling or flaking bark are White Birch, Arbutus, Ironwood, Sycamore, Black Cherry, Shagbark Hickory, and older Silver Maple.

Trees with Thorns:

Bark and thorns of the Honey Locust (Photo credit: Wikipedia)

There are still other trees that produce thorns on them. The obvious answer as to why is for their defense. Thorns deter animals from eating the tree or its fruit. Examples of trees with thorns are Hawthorn, Honey Locust, Acacia, and several types of citrus trees like Lemon, Lime, Orange, Grapefruit and Kumquats.