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Meet a Tree

Meet a Tree Booklet

The Tree

The best known member of the forest community is the tree. What is a tree and how does it grow? It is one of nature’s marvels.

Trees are the world’s largest plants. They have a single woody stem, a root system and a crown of branches and leaves. Each of these parts performs a special function or job. The cellulose fibres in the woody stem give the tree strength; the roots collect water and nutrients from the soil and transfer them through the stem to the leaves.

The needles or leaves of a tree may be small but the work they do is important. They allow the tree to breathe, to release moisture and oxygen and to use sunlight to manufacture food through a process called photosynthesis. This “food”, mostly sugar and other carbohydrates, provides the energy needed for the tree to grow.

The stem, or trunk of the tree, is made up of several specialized parts. The heartwood, the non-living core of the tree’s stem, gives it strength. The living sapwood surrounds the heartwood. It is through the sapwood that water and nutrients travel, from the roots up to the leaves, where they are changed into food by photosynthesis. The downward passage of food from the leaves, to other parts of the tree, occurs in the inner bark. The cambium, the thin yellowish-white layer found between the sapwood and the inner bark, performs the important job of making new cells every year, allowing the tree to grow. Covering the outside of the tree is the outer bark, which acts as a protective shell for the tree.

Each tree has its own growth chart. Within the tree’s structure, the story of how it has interacted with its surroundings is told. A tree grows in layers, one layer for each year. If you cut through the trunk you will see the inside of the tree and the layers will look like rings. The age of the tree can be told by counting the rings. Any changes in climate, weather, soil or light will affect how the tree grows. Good conditions means the tree will grow well and the rings will be farther apart. A cold, dry year means less growth and the rings will be closer together. Trees that are overcrowded will grow less as they fight for sunlight, moisture and nutrients. Thinning (removing trees) can prevent overcrowding.

There are 5 major layers of cells within a tree. Look at page 25, titled “The Layers of a Tree”, and find the 5 layers. Now read about these layers.

HEARTWOOD
This is the oldest part of the tree. Most of the wood in the trunk of an old tree is heartwood. The cells are dead and serve to support the tree. Sometimes the heartwood can rot or be eaten out by animals. When this happens, a large hollow forms inside the tree and it becomes an excellent habitat for a variety of creatures to live in.

SAPWOOD
Surrounding the heartwood is a layer called the sapwood (or xylem) that is made up of straw-like tubes used to transport water and minerals from the roots to the rest of the tree. As the sapwood ages, it usually gets filled with resin-like material and dies, forming part of the heartwood. New sapwood cells are produced by the cambium layer.

CAMBIUM
Next to the sapwood is a very thin layer of cells called the cambium. It is this layer that produces all the new cells in the trunk, making it grow thicker each year (palm trees do not do this). On the inner side of the cambium, new sapwood cells are produced. On the outer side of the cambium, new inner bark cells are produced.

INNER BARK (phloem-pronounced floam)
The inner bark cells consist of a series of straw-like tubes used to transport sap (containing glucose produced in the leaves during photosynthesis) from the leaves to feed the rest of the tree. It also carries sugars, stored in the roots, to the rest of the tree in spring when the tree is starting to grow again. It is this flow that is tapped in sugar maple trees to make syrup.

OUTER BARK
The outside layer on a tree is its bark. Different trees have different colors, textures, and thicknesses of bark but it all serves to protect the tree from disease and damage. The bark is made of dead inner-bark cells that are pushed farther away from the cambium layers as new inner bark cells are produced. As the tree pushes outward, the bark often splits and peels under the pressure.

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