This may seem like an easy question at first. We see trees everywhere and we know what they are when we see them, but what is it that really makes a tree, a tree?
The first part of the description is fairly easy. A tree has a woody stem and is a perennial, meaning that it lives for many years. However, there are bushes and other plants that fit this description and aren't really trees. There actually isn't a scientific description of a tree, so most people and books use a rule of thumb. If a plant has a woody stem, is a perennial, and grows to more than 13 feet tall, then it's a tree. Of course, there will always be tree-like bushes and bush-like trees, but, for the most part, we know a tree when we see one.
Types of Trees
Conifers and Evergreens
Coniferous trees have narrow hard leaves called scales or needles. Most of them are evergreen, meaning that they stay green during the winter and don't have leaves that change colors and drop during autumn season. Conifers get their name from having cones that house their seeds. Some examples of coniferous trees include cypresses, pines, cedars, firs, and redwoods.
Conifer trees are famous for having the tallest and largest forms of life. These trees are the giant sequoias or redwood trees. They can be found at Redwood National Park in California. The giant redwood trees grow to 115m (379 feet) tall. That's a tree taller than a football field is long!
Deciduous and Broadleaf Trees
Another type of tree is the broadleaf. Most broadleaf trees are deciduous, meaning that they shed their leaves each fall. The name broadleaf comes from their wide leaves, unlike the thin needles of the conifers. These trees also produce flowers. Sometimes the flowers are in the form of fruit or nuts, which we can often eat. Some examples of broadleaf trees are oaks, beeches, maples, elms, and birches.
How do trees grow?
As trees get older they grow taller, wider, and deeper. Trees grow taller by growth from new cells at the tips of their branches. They also grow deeper in the form of roots in the ground which collect water and nutrients from the soil. The roots grow at the tips like the branches. Trees also grow wider in their trunks and branches. This growth takes place at the outer later called the cambium. Since growth of the cambium stops during the winter or cold months, tree trunks develop rings. Each ring represents a year of growth. We can see how old trees are by counting their rings.
Diagram of rings in a young conifer from Fritts, 1976
Other Tree Features
Leaves - The leaves on a tree are important for gathering sunlight for photosynthesis. Some trees have small or narrow leaves, and some trees have huge leaves.
Bark - Bark is the protective covering, sort of like skin, for tree branches. Bark protects the tree from animals and even diseases.
Trees and Humans
Trees have provided humans with building materials for homes, furniture, and more throughout all of human history. Trees have also been a great source of fuel as fires for keeping warm and cooking food. We also gather a lot of our food from trees such as fruit and nuts. However, trees are also important to our environment. Trees are a primary source of oxygen. They breathe in and reduce carbon dioxide and in turn provide oxygen. We couldn't live without trees! On top of that trees provide us with shade and beauty, so be sure to hug a tree today!