it stable. Contrary to the commonly held misconception about trees having extremely deep root systems, 90% of a tree’s water and nutrient absorbing roots are found in the upper 18” of soil. Having a better understanding of where a tree’s roots are located, and how vulnerable they are, is critical information for any tree owner who may be remodeling and having construction activity on their property. Badly planned construction activity around a root system can eventually kill a tree.
Layers of a Tree
Starting from the outside of a trunk, the first (and usually only outwardly visible) layer of a tree is the bark. Think of bark as the outer skin of a tree. It is a protective covering and is composed of mostly dead cells. Bark keeps moisture and gases in the tree and helps a tree resist attacks by insects and disease. Exploring the center of the tree, the next three layers beneath the bark are phloem, cambium, and xylem. Cambium is a thin layer of cells that are critical to the growth of a tree. The cells of the cambium change to give outward rise to
phloem and inward to xylem. In general, the phloem transports sugars and growth-signaling hormones throughout the tree. Xylem transports water and nutrients from the roots up to the leaves. The active outer portion of xylem is also known as sapwood. The older, inactive parts near the center are heartwood. Heartwood is darker, stronger, and more resistant to decay.
Heartwood provides additional support for the tree. Trees are a wonderful marvel of self-sustainability. They absorb water, nutrients, carbon dioxide and sunlight to produce their own sugars via photosynthesis and can even store their sugars for later use in the form of starches -- all while reaching 100 plus feet into the air and remaining anchored during heavy winds.
The most visible parts of a tree are its first line of defense. Bark and tree roots are where trees often experience construction damage. High winds and other factors can shred and break even the largest limbs of a tree. As tough as trees are, preventing injury to their roots and bark is critical. Fortunately, most wounds to a tree do not lead to decay or hollows. Trees have an amazing ability to survive the most adverse conditions. Xylem is one of the tissues that transports water and nutrients through a tree. This shows where xylem is located in the trunk. Active xylem is sapwood, as shown in the tree trunk illustration.
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