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WHY ARE TREES SO IMPORTANT?

Trees release oxygen into the atmosphere for other

organisms to breathe in. The roots of trees bind soil

together, preventing it from being washed away. Trees

also provide food and habitats for many animals, and

wood for fuel, timber, and many other products.

HOW DO TREES GROW?

Trees grow in two ways. Special cells at the tips of

twigs divide, making the twigs grow. Also, a layer

of cells under the bark, the cambium, divides,

widening the trunk and branches. The new cells that

the cambium makes form a visible ring inside the trunk.

WHAT ARE BROAD-LEAVED TREES?

Unlike conifers, with their needle-shaped

leaves, these trees have wide, flat leaves.

Many are. DECIDUOUS TREES that

lose their leaves in autumn, but the

broad-leaved trees of a tropical rain-

forest are evergreen. The mass of leaves

of adjacent trees form a. CANOPY.

1 TYPES OF LEAF

Broad-leaved trees have one of

two types of leaves. A simple leaf

is undivided and has its own leaf

stalk. A compound leaf is divided

up into several smaller leaflets

that are attached to the main

leaf stalk.

1 EVERGREEN RAINFOREST
The Amazon rainforest is the
largest in the world. It contains
about one-fifth of all flowering
plant species.

4 TREE TRUNK CROSS-SECTION

The inside of a tree trunk has rings of outer

sapwood and inner heartwood. Both consist of

strength-giving cells called xylem. Sapwood xylem

also carries water and minerals up the tree.

Outside the sapwood are phloem cells,

which carry food, surrounded by bark.

HERCULES CLUB

(COMPOUND

LEAF)

Fibrous bark consists of dead

cells and protects the trunk

Cambium

Phloem carries food up or down

the trunk

Heartwood contains

mostly dead cells

Sapwood is made up

of living cells and

carries water

and minerals

Growth ring indicates

one year’s growth

Trees

These tall, seed-producing plants have a single woody

stem, called a trunk, that supports their great weight.

They live for many years and do not die in winter.

The largest group of trees is broad-leaved trees.

INDIAN BEAN TREE

(SIMPLE LEAF)

leaves branch out like a net.

• Palm trees, with about 2,800
  species, are monocot flowering
  plants. The veins in their leaves
  are always parallel.


• Conifers, with 550 species,
  have cones instead of flowers.

Trees are divided into three

groups: broad-leaved trees,

palms, and conifers.

• Broad-leaved trees are the
  largest group, with over 10,000
  species. They are dicot flowering
  plants, and the veins in their

TREE CLASSIFICATION

trees