Tree

A tree is a woody plant with a strong stem (woody trunk) that lives for many years, typically grows tall, and produces branches and leaves. The term 'tree' does not refer to a single category; it is a structural description. Many plants of different families have this form.

The distinction between a tree and a shrub is not sharply defined. Generally, a tree is characterized by a single large stem reaching considerable height, while shrubs begin with many stems from the ground. The height threshold used to make this distinction varies from region to region.

Parts of a tree

Roots extend into the soil to absorb water and nutrients, and they anchor the tree. The trunk transports water and food to the upper parts and contains conductive tissues: xylem, which carries water upward, and phloem, which carries food downward. The bark on the outside protects against injury and pests. The branches and leaves carry out the function of light capture.

How it works

Photosynthesis occurs in the leaves—a process in which light, water, and carbon dioxide are converted into sugar. The tree releases oxygen. Water exits through tiny pores on the leaf surface (stomata) in a process called transpiration, which aids water movement through the trunk.

Growth and age

Many trees in temperate climates produce new wood annually, which creates growth rings that can be used to determine age. Trees in regions with uniform seasons sometimes do not form clear rings, as the seasons are similar. Some species live for hundreds of thousands of years.

Role in the environment and for people

Trees provide shelter for birds, insects, and other animals, and they reduce air pollution. They store carbon in wood and vegetation, which affects climate. People obtain wood, fruit, medicines, fuel, and shelter from trees. In Somalia, trees such as the acacia and incense tree are the source of economically important gum products.