The 5 Layers of a Tree Trunk

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The anatomy of a tree would truly interest even the most apathetic person. That is because trees are complex parts of nature that provide an infinite list of benefits and an even larger amount of value! There are thousands of tree species in the world, all in different shapes, sizes, colors, yields, and more. But one thing they all have in common: a trunk. All trees, both deciduous and coniferous, have a tree trunk in some form or another. And one of the most interesting facts about tree trunks is that they have 5 different layers! Continue reading to learn more about each layer of tree trunk and the purpose they serve.

Tree Trunks

As mentioned, tree trunks have 5 separate layers to them. They are the outer bark, inner bark (phloem), the cambium cell layer, sapwood, and heartwood. Each layer has their very own purpose, but overall, the trunk’s primary job is to protect and support the tree. Look below to review each layer and what they do.

Outer Bark:

Like a shield, a trunk’s outer bark is there to protect the tree from its outside surroundings, including inclement weather, wildlife, pests, and more. It also controls moisture, by both preventing excess moisture in the rain and snow, and retaining sufficient moisture levels during dry seasons. It also provides insulation in cold weather and protects against sunburn in the summer.

Phloem (Inner Bark):

The phloem, or inner layer of bark, is where food and nutrients are passed through the tree. This layer has a very important job, but a very short lifespan. It eventually dies, turns to cork, and becomes part of the outer layer of bark!

Cambium Cell Layer:

The cambium cell layer is interesting because it is the part of the trunk that grows. Each year, this layer produces more bark and wood as a reaction to the hormones being passed down from the leaves along the food pipeline. These hormones are called auxins, and they are very important because they stimulate new cell growth!

Sapwood:

Sapwood is new wood, and serves an important role as the tree’s water pipeline, delivering water to the entire tree. And as new sapwood is created, the inner cells lose their vigor and turn to heartwood.

Heartwood:

Heartwood is the most inner part of the trunk. It plays an important role in balance, stability, and security for a tree. Technically, heartwood is dead, but it does not atrophy or decay (unless the outer layers are jeopardized). It is made up of a hollow, needle-like cellulose fibers that are joined together by a glue-like chemical called lignin.

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Source by Sarahbeth Kluzinski