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The Anatomy of a Tree

Can you identify a tree by its bark? That’s right! You can tell the type of tree just by looking at the type of bark. There are many different types of trees, and they all have unique characteristics. For instance, some trees might be smooth while others might be bumpy or rough. So take a look at your favourite tree and see if you can identify what kind it is! 

Did you know that there are over 100,000 different species of trees in the world? The word “tree” comes from an old Indo-European root meaning to grow strong and straight – which is exactly what these living beings do for us every day.

Trees are one of the most iconic natural structures on earth. They can be found in any climate and come in various shapes, sizes, and colours. This blog post will teach you about the anatomy of a tree as well as how they grow. 

Some common types of trees include deciduous (those that loose their leaves), evergreen (those that keep their needles or leaves year-round), coniferous (trees with needle-like foliage) and palms (tall trees with sturdy trunks). 

Some people plant them for shade, decoration, food production and provide an ecosystem habitat for animals such as birds and squirrels. But what is the inside story? What do we need to know about trees? 

Parts Of A Tree

The major parts of a tree are leaves, flowers and fruit, trunk and branches, and roots.

Leaves

Leaves are basically sheets (or sticks) of spongy living cells connected by tubular conducting cells to the “plumbing system” of the tree. They are connected to the air around them by openings called stomates and protected from dehydration by external wax layers. In addition, they frequently have hairs, bristles, scales, and other modifications that help adapt them to their environment.

Trunk And Branches

While branches and trunks may seem to be “just made of wood,” this material (and the bark around it) consists of many types of cells adapted for strength, resistance to injury and decay, transport of liquids, and storage of starch and other materials.

The bark consists mostly of two zones: The inner bark or phloem actively contributes to the tree’s life processes: its tubular cells form the “plumbing system” through which sugar and growth regulators, dissolved in water, are distributed to other parts of the tree from the leaves and buds where they are made.

The outer bark consists of layers of inner bark cells that have died and cracked as they have been pushed outward by the tree’s growth; outer bark forms the tree’s first line of defence against damage by insects, people, heat and cold, and other enemies.

A tree normally has three meristematic zones — that is, cells that can divide and reproduce themselves. Two of these, the root tips and the buds at the tips of twigs allow the tree to grow lengthwise. The third, located between the bark and the wood, is the vascular cambium zone, often referred to merely as “the cambium.” 

Its cells divide inward and outward, laying down new wood cells on those already in place and new inner bark cells inside those already existing. The cambium is one important key to trees’ success. Its growth from the outside outward allows the tree to cover over minor wounds and (as we will see later) to wall off and abandon entire columns of rot infected wood. This is the strongest of all a tree’s defences against decay. 

Inside the cambium, the region is the xylem or wood. Xylem includes three principal types of cells. First, numerous tubular conductive cells are running parallel to the trunk or branch that they form and adapted to carry water and minerals upward from the roots. Second, there are also sheets of ray cells — tubes running from the inner bark inward toward the centre of the tree. 

The third type is parenchyma (pa-REN-ki-ma); while they are still alive, they warehouse starch crystals made by the action of enzymes on sugar. This starch, reconverted to sugar by enzymes, is the principal raw material for the natural fungicides made by trees in response to injury and the principal energy source for growth after injury. Parenchyma can also become meristematic under some conditions, taking on a role similar to the vascular cambium when a tree has been injured.

Various species of trees also have other types of cells, such as resin ducts, fibres, and tracheids. However, conductive cells, ray cells, and parenchyma make up the bulk of the wood and perform most of its functions. In heartwood-forming species such as redcedar, walnut, and oak, there may be a distinction between the newest, living layers of sapwood and heartwood. 

True strong>heartwood is the result of aging in the normal compartments of a tree. As sapwood becomes less involved in transporting and storing energy for the use of the tree, its cells become “toxic waste dumps.” This gives the wood a distinctive colour and sometimes gives it a natural resistance to decay. Unlike sapwood, heartwood can not respond to injury by forming antimicrobial substances; however, it can discolour.

False Heartwood” is a central column of discolouration that occurs as a young tree matures when many branches die and are shed even though there may be no decay. Discolouration that takes place in the early stages of decay after a tree is injured is not true heartwood, but it can keep heartwood from forming.

Inside the earliest wood in a trunk or branch is a column of spongy, styrofoam-like material called pith. Eventually covered over by layers of wood, pith is the remains of a primary tissue formed as a twig elongates. In some species, it disintegrates or is crushed; however, it remains in other species, such as black walnut, whose twigs can be easily recognised by their chambered pith.

Branch Attachment

tree-field

Until you understand the differences, all branches look pretty much alike. But the differences between forks, tree branches, and epicormic sprouts (sometimes called “suckers”) are profound and important.

Knowing them could save your tree, your house, or your life. When a tree is young, its goal is to get its head above the competition and catch as much sunlight as

possible. In the forest, where trees compete for light and space, the most efficient way to do this is with an “excurrent” growth habit — that is, a single, undivided stem and lateral branches. 

As it reaches its mature height, the branching habit becomes “codominant” — that is, its stem and branches often subdivide with forks instead of true lateral branches.

But when we domesticate trees, we encourage them to make this transition much earlier in life… and closer to the ground. 

In fact, a standard nursery practice has been to force trees into a codominant branching habit. A fork near the tip of a branch has little effect on the tree’s strength; but the lower the

a fork occurs, the worse the problem if it fails. 

True Branches

A true branch results from a process that starts with the growth of a bud into a twig. Normally this begins from the axillary buds found where each leaf joins the twig. Next, the meristem (reproducing cells) at the tip of the bud divide, and the newly formed cells become a twig. Finally, the meristem just under the bark — the vascular cambium — continues to divide so that the twig grows in diameter, forming a branch.

At the base of this twig is a swollen area called the branch collar. In this area, the wood fibers of the trunk (or parent branch) veer around the twig on each side and continue toward the trunk or the base of the tree; the “plumbing system” in the branch also turns groundward — none turns upward or goes around the trunk or parent branch. Since growth occurs at different times in various parts of the tree, the twig and branch fibres tend to form interwoven layers, a little like the laminations in plywood. 

Together, they create the extra wood thickness of the branch collar, which continues to grow as the twig matures. If the fibers in the crotch at the base of the twig knit well with those of the trunk or parent branch, a bark ridge emerges to some extent across the crotch.

Also, natural fungicidal materials saturate the fibers in the base of the growing twig, forming a protection zone; this does not happen in the trunk or parent branch fibres. This has important implications for pruning: if you cut only the protected branch fibres

outside the collar, you protect the tree from decay.

Forks

A fork is a place where a stem grew in two or more directions instead of one. Although one side may be larger than the other, neither side has any natural chemical protection. As a result, most U-shaped forks, with all bark visible, are dependable. The problem is with V-shaped forks, particularly when bark disappears down into the fork from each side, and much of the branch junction consists of two bark faces pressed against each other. 

Such forks, though graceful, have many potential problems:

  • First, there is no bond or strength between the two bark faces.
  • Second, as the two sides of the fork grow, the pressure between them tends to spread the fork, increasing the splitting force on its the base.
  • Third, this pressure also crushes the living tissues under the bark, starving this area and destroying its defences.
  • Finally, rainwater, fungus spores and other materials seep down into the fork, rotting bark and wood so that the weaker side is likely to split from its own weight or under wind stress. 

There is no way to know how much bark is included in a fork or how soon it may fail. Therefore, when rods and cables are used to reinforce weak forks, they must be installed properly and inspected periodically. 

Too often, such hardware merely postpones the failure of the tree until it is bigger, heavier, and more dangerous. The only good way to deal with such forks is to prune out the weaker side while the tree is still young. Such preventive pruning pays for itself many times over.

Epicormic Shoots (“Sprouts” or “Suckers”)

As a branch or trunk leader grows, its tip bud manufactures a growth regulator that suppresses buds nearer the tree’s base. But when the tip bud dies or is removed, many axillary buds (in the the angle between each leaf and its parent twig) and dormant buds (in the living wood under the bark) are activated, and the cambium may be stimulated to produce new adventitious buds (usually in response to wounding).

Sometimes, if they are carefully managed, suckers can sometimes be trained to become healthy and useful parts of a tree. As a rule, however, sucker growth that occurs as a distress response when a tree is in trouble is likely to cause further trouble. This is because suckers are superficially attached to the surface layers of wood and because most rapidly formed wood (such as that typically found in suckers) is weak.

Under ice load or strong wind, the tall spear-like suckers formed around topping cuts are especially likely to bend over and break; or they may tear out where they are attached to the surface layer of the stub, which has been opened up to serious rot.

People want their trees to “look like trees” — that is, to have a large, shady crown; and we think of multiple stems as “graceful,” not understanding that this beauty often comes at the expense of strength and safety. At first blush, this would seem to force us into a choice between beauty and strength. 

But the more we understand about trees, the more we appreciate healthy structures. It is difficult to remain enchanted by something that is likely to split open and crush anything in its path. 

Difference Between A Branch And A Limb

Structural pruning is a vital part of any tree’s life. It promotes healthy and stable landscape trees growing in urban environments. And when correctly done, it can increase your tree’s lifespan and safety.

Structural pruning is about improving the branch architecture within a tree’s crown area to create a central and stronger leading stem with a network of adequately spaced branches of lesser diameter growing alongside.

The overall purpose of structural pruning is to prolong the lifespan of your landscape or yard tree.

What Is A Branch?

A branch refers to the woody structure of the tree that grows from its trunk or stem. It’s, however, not part of the central trunk and can be a small division from another branch or outgrowth.

Its main function is to facilitate the transport of water and nutrients from the tree’s trunk to the leaves. Branches also act as key support and balance structures for the fruits, flowers and leaves.

  • First-order branches – Branch that connects from the trunk
  • Second-order branches – Smaller branch growing off first order branches
  • Thrid-order branches – Smaller still growing off second-order branches

What is a limb?

A limb refers to a large or the primary division arising from the trunk of the tree. Most experts estimate it to be at least 4 inches bigger than a standard branch.

Its main functions are very similar to that of the branches, although it may sometimes take the role of the trunk in some trees.

Tree Branch Anatomy

trees-forest

There are numerous parts of a tree that all work together to ensure it remains healthy and fruitful. Among the most important parts include;

  • Leaves – Leaves are the flattened green blade-like structures found on every tree. They are responsible for photosynthesis (food production) and transpiration (respiration) for the tree. Depending on their location, the leaves may develop adaptive features such as hairs, bristles, scales etc.
  • CrownThe tree crown refers to the upper visible part of the tree. It includes the tree branches, limbs, leaves and flowers, and starts at the level of the first branch. The shape of the crowns is different for most trees.
  • Branches – Branches arise from the trunks or limbs of the tree forming part of the crown. They extend to have twigs that hold leaves, flowers and fruits for some trees. In addition, the branches are important for the support and transport of water and nutrition from the trunk to the leaves.
  • Trunk – The trunk is the centre structure of the tree where branches and limbs grow from. It connects the tree from the roots allowing transport of food, nutrients and water to all parts of the crown. Trunks also raise leaves above the ground to receive adequate sunlight. It’s made up of the outer bark, inner bark, cambium cell layer, sapwood and heartwood.
  • RootsThe roots are arguably the most important parts of the tree. The underground roots network is responsible for the tree’s anchorage, absorption and uptake of water, minerals and oxygen, transport to the trunk, growth and storage. The root structures for trees also differ depending on the species.

Difference Between Branches And Twigs

The biggest difference between branches and twigs is their size. Twigs are usually much smaller and grow from branches or even small bushes. Therefore, they can be easily defined as the ‘smallest’ branches.

However, some trees may have larger twigs than the branches of another tree, i.e. twigs of an Oak tree may be bigger than that of a cherry tree.

Another key difference is that twigs have leaves growing directly from them. On the other hand, branches grow from the trunk and can be significantly large, such as boughs or lateral branches.

What Are The Boughs Of A Tree?

Boughs refer to the large or primary branches of a tree. They grow directly from the trunk and hence can be interchangeably called limbs. However, most people, including tree experts, avoid these terms and opt to use the word ‘‘branch’ in conversation.

Bough vs Branch

The main difference between a bough branch is its size. Therefore, boughs are usually associated with branches bigger than the average-sized branch on a tree.

Another key difference is that boughs can only grow from the trunk. On the other hand, a branch can grow from a bough or limb, trunk or another branch.

In terms of functions, boughs and branches perform the same activities. Therefore, they are crucial in supporting foliage development and may have some small branches and twigs growing from them.

Their shape and structure, like branches, also vary depending on the different types of trees.

What is the main branch of a tree called?

The main branch is known as the bough. It’s unique because of its large size and girth. Other subdivisions from the trunk are plainly known as branches, while the smaller divisions from the branch are called twigs.

Trunk vs branch

The trunk of the tree is the vertical wooden part that connects the crown to the roots. It’s also the part from which all branches grow and gain their water and nutrients.

Once the roots absorb water, oxygen or nutrients, they are transported to the trunk, which then distributes them to the branches and boughs. Branches finally deliver the nutrients to the twigs and leaves.

Stem vs Trunk

For trees, the stem refers to its trunk. However, this isn’t the case for all plants. This is because the term trunk is often associated with ‘woody’ plants.

In botany, the experts use the word stem when referring to plants that aren’t naturally woody. So, in essence, all trunks are stems, but not all stems are trunks.

Another difference between these two tree parts is that most stems can photosynthesise while most trunks can’t.

Trunk And Branches

Trees have the more permanent structure of a trunk and branches. This is the main difference that separates trees from plants. Trees having wood at their core make them more resilient, helps give them their incredible lifespans and making their branches more suitable for artistic pruning.

The main purpose of the trunk is to raise the leaves above the ground, enabling the tree to reach the light and survive. It also performs the task of transporting water and nutrients from the roots to the above-ground parts of the tree and distributing the food produced by the leaves to all other parts, including the roots.

 A cut across a tree trunk provides an inside view of the different layers.

  • Pith: The centre of the trunk and the initial provider of nutrients of the sapling. Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant.
  • Heartwood: The densest, heaviest part of the trunk and its wood is commonly the darkest colour.  The inactive xylem cells of the heartwood’s function chiefly to give strength to and support the tree and also is important in the tree physiology because it is a storehouse for sugars, dyes and oils. 
  • Sapwood: Xylem, or sapwood, is the third layer of vascular tissue. It is made up of thick-walled cells that transport sap from the roots to the crown-like the phloem.  Xylem represents the young wood of the tree and is light in colour. As xylem cells age, they become inactive and become the tree’s heartwood.
  • Cambium: An outer growth layer that creates both sapwood and phloem, increasing the tree’s thickness. In climates with distinct seasons, the tree adds a new cambium layer each growing season. This expands the girth or the trunk (and branches) and produces annual rings, which can be interpreted from a coring or by felling to determine the tree’s age. 
  • Phloem (inner bark): The next layer after the cambium tissue and before the bark. Its purpose is to move sap transformed from leaf photosynthesis, which contains sugar, around the tree and back down to the roots.
  • Bark: The outer layer that protects the tree and varies from species to species. A tree’s trunk and branches have a covering of bark.  The bark derives from dead phloem cells, which are shed outward.  It has multiple functions, insulating the tree from excessive heat, including fire resistance or cold and protecting insects and diseases. Bark may be very thin or up to 6 inches thick as in the cork oak; it can be of variable colour; it may contain tannins, and the surface may range from smooth to deeply furrowed.  Depending upon the species, dead bark can flake or peel off in patches or strips. Bark characteristics provide the key to tree identification and exhibit a distinctive appearance in the garden.  
  • Growth Rings: Each year of growth creates a new ring of sapwood that is visible.
  • Medullary ray (wood ray): Living cells that run across the growth rings that allow sap transportation radially.

Therefore, boughs

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