Exploring the Anatomy of Trees
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Trees are found in nearly every corner of the world and without them, the Earth would be a vastly different place. They generate oxygen for us to breathe, collect rainwater, and have even been shown to lower the risk of domestic violence when planted in residential areas.
But what are trees, and how are they made up? Let’s go on a journey of discovery to find out more about these magnificent parts of nature.
Main Parts of a Tree
Trees are made up from several parts, each with its own purpose. From the supporting trunk to the leaves that aid in photosynthesis, every part of a tree is important.
Crown
It sounds rather regal and the crown of a tree is pretty majestic; this is the mass of branches and leaves that make up the bulk of the structure. Beginning at the point where the first branches sprout from the trunk and ending at the very top, the crown is also where you may find fruit and flowers.
Tree crowns can differ wildly in appearance. Some are tall and narrow and don’t give much shade on the ground, while others are widely spread and create a large canopy.
Trunk
The trunk is the wooden, bark covered part of a tree that offers support to all of the other parts like the crown and the branches. The wooden part of the trunk is strong but may be prone to diseases and rot, which is why it is covered in bark. A microscopic layer keeps producing new wood and bark over the course of the tree’s life.
These vertical structures also connect the tree to its roots and provide a route to transport water and nutrients to the crown. It is the xylem or sapwood that is responsible for this transportation, while the heartwood is what holds the tree in its upright position.
There are some trees whose trunks are even able to store organic materials like sugar to store for later use.
Interestingly, while the trunk has several functions, its primary function is to raise the leaves high above other plants to get the most light.
Roots
Roots are what anchor the tree to the ground and stop it from simply toppling over. However, they are also important since they are what the tree uses to absorb nutrients, minerals, and moisture from the ground.
Some roots can be seen emerging above the surface, and these shallow roots are woody and usually grow within the first 12 inches (30 cm) of the soil. They do not grow any deeper than 7 feet (2 meters) but can have a very wide spread that’s sometimes taller than the tree itself.
There are also taproots that grow straight down and are what all the other roots grow from. These roots also deliver nutrients to the tree and promote new growth. A large tree may have as many as 30 miles (48 km) of roots hidden under the ground.
Tree Crown Shape Types
You only have to look at a group of trees to see how different each of them appears and this is largely due to the shape and size of the crown.
Full Crown
Trees with a full crown are among the most balanced and have an even number of branches. For this reason, they are often used as shade trees and to make an area look good. An example of this would be the maple tree.
Pyramidal/Conical Crown
Conical crowned trees are those whose crown has a wider base than it does tip; they taper towards the top. Sometimes, these trees, which can include things like the spruce, have branches that start a lot further down the trunk than other species meaning that sometimes, the trunk cannot even be seen.
Spreading Crown
The oak is one of the most well-known trees with a spreading crown and makes an excellent shade tree. These crowns are a lot wider than they are tall, and as such, this affects the length of the trunk, which is typically a lot shorter.
Weeping Crown
Trees with a weeping crown like the willow and elm, have much thinner branches that droop downwards. These are very aesthetically pleasing trees that are frequently used in landscaping but are also great shade trees.
Columnar Crown
A columnar crown, as its name suggests, has a more column-like shape with short branches whose length is very similar throughout the tree. These trees are usually much taller and narrower and are ideal for lining walkways which are how they’re commonly used in landscaping.
Tree Bark Anatomy
When we look at a tree from the outside, it would be easy to think that there was just one aspect to the bark. However, this is a part of the tree that has multiple layers, each one having its own purpose.
Outer Bark
The main function of the outer bark is for protection for the tree. It can act as a barrier to protect against insects that might invade the tree and also provides insulation.
Much more than this, the outer bark helps to control moisture. It’ll keep it in when there is not much moisture in the air but will prevent water from seeping in and causing damage to the tree.
Inner Bark
The inner bark, also known as the phloem, contains channels that help to move sap around the tree. Sap is a food source made by the tree.
Interestingly, the inner bark doesn’t survive for very long and has to be continually regenerated. However, once it dies, it turns into cork and adds another layer of protection to the outer bark.
Cambium
The cambium is a cell layer whose main job is to ensure that the trunk, roots, and branches of the tree continue growing healthily.
As hormones move through the inner bark with the sap, this stimulates new growth on an annual basis.
Sapwood
Sapwood, also known as xylem, is the part of the bark that sits along the outermost edge of the phloem. It is a cellular layer that is responsible for moving minerals and water from the roots up to the leaves.
Heartwood
The heartwood is the central part of the tree whose main job it is to support the entire structure. Surprisingly, this part of the tree is actually dead wood, but it remains strong because of the layers that surround it.
In fact, this part of the tree is so strong that just a small piece of heartwood could support as much as 20 tons thanks to a natural glue called lignin that holds everything together.
Lifecycle of a Tree
Just like animals and other plants, trees go through various stages of life which combine together to create its entire lifecycle.
Seed & Seedling
Trees begin life as a tiny seed, and when it is planted in the right conditions, the seed will germinate or sprout. These are the very beginnings of what is set to become a mighty tree, but for now, everything is happening below the surface of the ground.
Once the sprout breaks the surface, it becomes known as a seedling. Many trees don’t make it past this stage as the tiny green shoots are often gobbled up by wildlife.
Sapling
If the seedling survives and grows to be a little bigger, it becomes a sapling (generally any tree over three feet (91 cm)). Saplings look a little different from mature trees, with much smoother bark and a more flexible trunk.
How long the tree remains a sapling that doesn’t bear fruit largely depends on the species. Shorter-lived trees like cherry will mature much more quickly than a long-lived tree like the willow.
Adult Tree
Once trees reach adulthood, they are classed as a mature tree. This is when they start flowering and producing fruit but for some species, like the oak, this could take as long as forty years! But keep in mind that they can live for hundreds of years in the right conditions.
When the tree reaches a certain age (which is determined by its species), it can be classed as ancient. Typically, these trees no longer bear fruit, and their trunks may become hollow while the canopy might shrink.
Death of a Tree
Some trees will stand for thousands of years, like the yew tree, whereas others only live for a hundred or so years. Regardless of how long they have lived, all trees reach a point called snag whereby the wood begins dying.
However, just because the tree is now made from deadwood, that doesn’t mean that it has finished playing its role for the local wildlife. It is at this point that those hollow trunks act as shelter for animals, so many local authorities don’t automatically remove dead trees.
Types of Trees
Trees can be one of two types; coniferous or deciduous. There are some key differences between them, including how they carry their seeds and the shape of their leaves as well as the conditions in which they will thrive. Let’s take a closer look at each type.
Coniferous
The word coniferous comes from the fact that these trees have cones which are where the tree stores its seeds in order to keep them safe from predators and the elements.
Most types of coniferous trees are evergreen, meaning that they do not shed their leaves, so they’re a common choice in gardens where greenery is required all year round. They’re also ideal for providing shade and shelter for birds regardless of the season.
The leaves of coniferous trees are needle-shaped and they tend to grow in clusters or rows. The wood is soft. Some examples of these types of trees include pine, fir, and spruce.
While they may not produce flowers or fruit, these trees can get very tall and are able to grow in a much wider range of soil conditions than deciduous species, even where the soil is not particularly rich.
Deciduous
Deciduous trees lose their leaves every fall. They do this for several reasons, including preserving energy through the winter and making it easier to store moisture in the trunk. However, these dropped leaves enrich the soil, which is a good job since these trees need good soil conditions in order to thrive.
Unlike the needle shaped leaves of the coniferous tree, deciduous trees have much broader leaves, and their wood is much harder. Some examples of these types of trees are oak, birch, maple, and mahogany. You’ll notice that most of these species are used for woodworking, furniture making, and other crafts, thanks to the hardness and strength of the wood.
Deciduous trees produce flowers and fruit, which is one of the many reasons people like to include them in their gardens. When they’re fully grown and have all of their leaves in summer, they also provide ample amounts of shade.
Why Do Trees Die?
Most trees will live much longer than any human or animal, but that doesn’t mean they are immortal. Just like any other living thing, a tree will eventually come to the end of its life, even if that’s thousands of years after the seed germinated.
Naturally, the ability of the tree to photosynthesize will eventually come to an end. This essentially means that the tree is no longer able to breathe, and this causes its demise.
However, if you’re growing trees in your yard then there may be certain factors that can affect their lifespan and even cause them to die prematurely.
The quality of the soil is one of the factors that could affect a tree. For example, it might not contain the right amount of nutrients or it could be too dry or too moist. Certain species require specific conditions, and it’s important for growers to ensure these are met to ensure the health of the tree.
In other circumstances, trees may become victims of disease, and there have been cases of entire forests being devastated by things like Dutch elm disease.
Diseases can enter the trees through wounds or simply through the leaves and once they take hold, it may not even be obvious for some time, at which point, the disease may be too far gone to treat. But it isn’t only pathogens that can cause problems, it’s possible for insects and parasites to get into trees and cause irreparable damage.
If you live in an area where forest fires are common then this could be a serious threat to local trees. Extreme heat, flames and even high winds can damage the tree so much that it is no longer able to thrive. In some cases, it may not die entirely but could be damaged to the point that it’ll stop being able to resist disease.
Other traumatic events like floods can cause a tree to die due to excess moisture. Where the weather is very cold and significant amounts of ice are deposited onto the tree, this can cause stress and structural damage, which may ultimately lead to death.
Of course, it isn’t only natural factors that can affect the lifespan of a tree, deforestation is a major problem in some of the world’s forests. While there are managed areas for harvesting wood that are overseen by the FSC, there is still a lot of illegal activity which is causing a significant decline in tree populations.
