The 5 Layers of
a Tree Trunk
* By Sarabeth Kluzinnski
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!
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.
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.
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!
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.
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