One of the most interesting facts about tree trunks is that they have 5 different layers! Continue reading to learn more about these 5 tree trunk layer, including what they do!
🌳 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.
❶ 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.
❷ 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!
❸ 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 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 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.
Additional Parts of a Tree Trunk:
The pith is made of soft, spongy parenchyma cells, which serve the purpose of storing and transporting nutrients throughout the tree. The medullary rays are cellular structures found in only some tree species., and appear perpendicular to the growth rings. The growth rings, also known as Dendrochronology, appear one at a time, once per year, darker in the fall and lighter in the spring and summer.
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