What is a tree?

Bursting buds ❯ Leaves and new stems sprout from buds that protect the soft, delicate tissue from winter frosts. The new growth makes the bud burst open.

Leaf is tightly folded inside the bud but soon bursts out.

Bud scales are tough and weatherproof.

Spring As the weather gets warmer in spring, leaves begin to sprout from buds on the branches. The green leaves use sunlight to make food for the tree to grow and produce flowers. Summer Long days of sunlight allow the tree to make lots of food, and the tree is thick with leaves and yellow flowers, which are cross-pollinated primarily by bees. When fertilized, the flowers will become fruits and seeds will form.

Through the seasons

A deciduous tree, such as this Norway maple, has a cycle of growth that follows the seasons.

Of all the plants, trees are the biggest and live the longest. Instead of green stems, they have woody trunks, which usually divide into many branches. The woody tissue is very strong, allowing some trees to grow to incredible heights of 330 ft (100 m) or more. A network of roots anchors the tree to the ground and draws up water and nutrients from the soil.

Fall As the days get colder and shorter, the tree stops making food. The chlorophyll that makes the leaves green begins to break down, and they change from green to red and gold and fall from the tree.

Deciduous or evergreen?

Winter In the cold winter months, the branches are bare and the tree lies dormant, preserving its energy and water until the following spring.

Leaves change from green to red.

Deciduous tree in fall Evergreen tree

There are two main types of trees. Deciduous trees lose their leaves in winter as they stop growing. In spring, they produce thin leaves that make food efficiently, so the tree grows fast in summer. Evergreen trees have tougher leaves that make food more slowly but stay on the tree all year long. The tough outer bark protects the layer of growing plant tissue beneath it.

Wide, pale rings form in spring, while narrow, dark rings form later in the year.

The heartwood at the center is the oldest part of the tree.

Cross section of a tree trunk

Every year, a tree’s trunk grows broader as a layer of woody tissue is added beneath the bark. The tissue grows fastest in spring, making softer wood, and more slowly late in the year, making harder wood. This forms annual growth rings, which are revealed if the tree is cut down.

Types of forests

Where there is enough rainfall for trees to grow in large numbers, they can form dense forests. The type of forest depends on the nature of the trees, which is determined by the climate.

Rain forest In wet climates with no winter frosts, trees grow all year round to create rain forests. These are mostly found around the tropics.

Coniferous The forests that grow in cold northern climates are mostly made up of tough evergreen conifer trees, such as pines and spruces.

Deciduous Regions with long summers and short winters have forests of deciduous trees. They lose their leaves in fall but grow new ones in spring.