WHY DO TREES HAVE BARK?

tall pine tree

You might not think too much while looking at a tree’s bark. But if you start getting into it, it is extremely interesting to learn about the topic. There are different kinds of bark and different components to each kind of bark. Each of these components serves a particular purpose for the tree. If you have recently started getting into nature, this topic can be very interesting to learn about. Let’s take a look at the basics of tree bark and why do trees have bark.

Barks serve multiple purposes, but the major use of the bark is to protect a tree from diseases and environmental conditions. Besides protecting the tree, the inner layer of bark is used for the transportation of water and nutrients from roots and leaves to other parts of the tree.

DIFFERENT TYPES OF TREE BARK

WHAT IS A TREE BARK?

Before we talk about different types of bark we should first look into what a bark actually is and what are the different components which make up a bark. To begin with, the bark is basically the outer layer of a tree or a plant. The bark is an all-inclusive term, which comprises any layer outside the vascular cambium.

The bark is formed when new layers of cells are added to the internal layers. As more and more layers are added, the already present layers are compressed towards the outside of the tree. These compressed layers usually make up of dead cells on the outside and this is known as the bark.

The basic usage of bark is protection. Each tree has a different type of bark which has evolved through millions of years to serve a particular purpose. Inner bark on the other hand is the transport system of the entire tree.

DIFFERENT COMPONENTS OF BARK

Tree bark has a lot of different components with extremely difficult scientific names and uses. We are not concerned with all of that here as it’s a topic for another article. I will try to go through the major components of tree bark as briefly as possible.

What most people know as the bark of a tree is known as the rhytidome. It is the most outer layer of a tree and if you were to peel off the first layer from any tree, it is the rhytidome that would come off. This is known as the outer bark.

The inner bark on the other hand consists of the secondary phloem and secondary cortex. The inner bark components comprise cells that are still alive. Though both the inner and the outer bark are outside the vascular cambium. The vascular cambium being the growth layer. The phloem is responsible for transporting the food to the entire plant. But it has a short life before it gets converted into rhytidome.

Another component of the bark is the periderm, this is further divided into sub-layers. The function of this component is protection against bacteria and insects. It also prevents water loss from the tree.

DIFFERENT TYPES OF BARK

  • SMOOTH BARK

You must have noticed that most of the barks are rugged and have cracks. When a tree is younger, they sometimes have very smooth barks. These usually crack up as the tree gets older. On the other hand, there are some species that have smooth barks throughout their life span. Some of these species include the Red Maple, American Birch, and Redwood, and Aspen.

  • PEELING BARKS

You might come across a tree with peeling barks. They look like loose hanging skin. This usually happens when the growth rate of the tree and the bark are not the same. When the tree is growing at a faster rate compared to its bark, the outer layer can start coming off. Pine or even a Paper Birch is an example where the outer layer starts peeling off in curly strips.

  • LENTICELS

Every tree has lenticels, they are the pores that are responsible for transporting oxygen and CO2 throughout the outer bark. Usually, you don’t see them as they are either hidden or very small. In some trees, they are visible in different shapes and sizes. Yellow Birch, for example, has horizontal lines which are actually its lenticels. Bigtooth Aspen on the other hand has lenticels shaped like diamonds.

  • RUGGED OR DEEP RIDGES

A rough bark entails that the rhytidome has gaps or cracks within it. There are two major types of ridges, intersecting or parallel. White Ash has intersecting ridges while Northern Red Oak has parallel ridges.

  • SCALES

The only difference between scales and ridges is the way that the outer layer left gaps within it. A lot of Pines and Spruce have bark scales. On the other hand, Black Birch consists of irregular and thick plates.

WHY DO TREES HAVE DIFFERENT TYPES OF BARKS?

Remember that every evolutionary step is taken because of a reason. Why some trees have smoother barks while others have rugged barks? The answer boils down to the tree’s needs and priority.

Smoother barks make it difficult for insects to burrow into it. For a tree to have a smoother surface, it needs to grow relatively slowly. So having a smoother bark tends to result in a slower growth rate. These kinds of barks also tend to take longer to seal injuries. Basically, a smoother bark is a defense mechanism to ward off attacks from insects, animals, and parasites. A Beech tree would be an example here.

huge beech trees with smooth bark
Beech Trees

On the other hand, trees that have a faster growth rate tend to have barks that get cracked or wrinkled while growing. These trees also have the advantage of a faster recovery in case of injuries. On the other hand, they tend to be prone to insects and parasites living within the bark.

One of the steps that trees make is to produce tannins. This makes the bark unattractive to insects. Rugged barks also tend to save water for the tree by reducing the surface for water to evaporate from.

Some trees like Birch will have a very thin outer layer. This layer tends to shed a lot. This is due to the moist and damp environment they are prone to. Moist environments tend to result in lichens and moss infecting the tree. With regular shedding, trees are able to avoid these diseases and parasites.

birch
Birch

WILL A TREE DIE IF BARK IS REMOVED?

Remember that bark is not just made up of dead tissues and cells. The inner bark consists of pipelines that transport water and nutrients to different parts of the tree. Think about this, a tree bark is like human skin. Once you remove it, our bodies are prone to infections and diseases or we might just bleed out.

If you remove a small part of the bark then the tree might survive. Usually, this amount is less than 25% of the circumference of the tree. Although still, you will have to take care of the tree to ensure its survival. If you remove anywhere between 25% to 50% of the circumference of a tree then it will become much harder for the tree to survive but with proper care, it still might have a chance.

With bark removal, the tree will lose some leaves and some branches but it can survive. If you remove a strip of bark from the entire circumference of a tree, it pretty much guarantees its death. (This is also known as girdling) The death will take up to a year as there is still stored food and water left in some parts of a tree.

IS THE BARK OF A TREE ALIVE?

The bark is divided into two major layers. The outer bark and the inner bark. The outer bark is made up of largely dead cells and tissues. But on the other hand, the inner bark consists of phloem which is responsible for transporting water and food from leaves to different areas of a tree.

We can say that some parts of the bark are dead while some parts are alive. It is a mixture of both: one dead layer that protects the tree from its surroundings and a second layer that acts as a pipeline transporting nutrients for the tree.

CAN TREE BARK GROW BACK ONCE REMOVED OR DAMAGED?

If there are small scratches on the bark, then the tree can heal itself. If there are large wounds or large parts of the bark have been removed then the tree becomes vulnerable. It takes a lot of time for the bark to form in the first place and a tree cannot regrow it in a matter of days or even months. It’s a great time for insects and diseases to attack the tree.

When there are large wounds present, the edges of the wound seal themselves up to prevent further damage.

The bark does not grow back, but the wounded area will eventually be covered by bark if the tree survives long enough. The main area of the wound will be open to the environment for years until the tree outgrows the damaged area. It can take years, in some cases decades for this to happen naturally.

evergreen tree bark wound

WHAT TO DO IF THE BARK HAS BEEN REMOVED OR DAMAGED?

Even if a small part of the bark has been damaged or removed you will have to take care of it to make sure the tree survives and thrives. There are two ways you can go about it.

The first method is simply cleaning off the area. This is very similar to what you would do with a normal human wound. You can clean a tree wound with simple water and soap. This will stop any insects or bacteria from infecting the tree. It is not recommended to use a sealant. It is better to let the wound heal itself in the open air.

If the damage to the bark is very rough or jagged, it will help the tree if you clean the area surrounding the wound. You can do this by removing some of the rough leftover bark around the wound.

The second method is bridge grafting. You should use this method if there is more damage to the tree. What you are aiming to do here is to provide an artificial bridge between the damaged areas so that the nutrients and water can be transported across the tree.

Take some of the twigs from the same tree and place them vertically connecting different parts of the tree. You are basically bridging the gap between the bottom and top of the tree which has formed because of the damage to the bark. You should fit these twigs, also known as scions underneath the barks of the different points. Cut off some of the damaged areas so that the twigs can be fitted underneath them. You should also use grafting wax to protect the area from drying out.

FREQUENTLY ASKED QUESTIONS

This topic can be very interesting if you start getting into the specifics. I will try to answer some of the most common questions that people have related to the topic. Just in case if you have any doubts.

WHAT IS GIRDLING?

Girdling is the act of removing a horizontal strip of bark around the circumference of a tree or a branch. This will slowly kill the entire tree or the branch.

HOW SHOULD YOU HARVEST THE BARK FROM A TREE WITHOUT KILLING IT?

If you want to use the bark for medicinal, food, or any other purposes the best way to go about it would be scavenging. Use barks from a dying or an already dead tree. Taking too much bark from a live tree can end up killing the entire tree.

DOES THE BARK OF A TREE DETERMINE THE AREA IN WHICH IT CAN GROW IN?

As I mentioned above, barks have evolved differently for different trees keeping in mind the conditions they evolved in. if you take a tree with a specific bark from tropical regions chances are that it won’t survive or thrive in polar or even temperate climates.

CONCLUSION

To sum it all up, barks consist of two major layers. The outer and the inner bark. The outer layer consists of dead tissue and cells while the inner layer is the transport mechanism for the tree. There are a lot of different types of barks with each type evolving for a specific reason. Some of these types are smooth, rugged, green, peeling, and lenticels. The bark is the protective system of a tree, if it gets removed or damaged to a certain extent the entire tree will end up dying.