Finding out where plants live
If you look at a tree in a park, you may think that it is doing nothing. If the air is still, it will stand silently. If there is a wind, its leaves may rustle and its twigs may sway. However, a tree, like all plants, is doing something every moment of its life. It is taking part in changes with its surroundings. These changes are taking place not just between the tree and the air around it: they are taking place between the tree and the soil too.

It may seem surprising, but you can get some idea of a tree's roots by looking at its branches. See how far the branches stretch out from the trunk. Look down at the ground below the tips of the twigs and imagine the roots. They stretch out about as far from the trunk as the branches do. Near the tips of the roots are tiny white hairs. They probe through the gaps between the soil particles and take up water. The gaps also contain air and the roots take in oxygen from the air to stay alive. Soils contain minerals, which dissolve in the soil water. The tree root takes up these too, so it can make food.

Above ground more changes are taking place. If you look along the twigs you may see small holes in the woody surface. The tree takes in oxygen through these holes to keep it alive. On the underside of the leaves there are holes too but you need a microscope to see them. The holes in the leaves can open and close according to changes in the habitat. In the day the holes open and let out water vapour. As the leaves lose the water vapour, they draw up water from the roots. They use the water to make food. Plants also need a gas from the air to make food. This gas is called carbon dioxide and the leaves take it in through their holes. When food is made, the leaves also produce oxygen. There is too much of this gas for the leaves to use so it passes out of the holes into the air. At night, when it is dark and the plant cannot make food, the holes close.

By thinking about the changes that a tree makes with its surroundings, we can see that a plant needs certain things from its habitat. If these things are present the plant can survive. If these things are not present you will not find the plant there. For example, when you look at a mountain top you do not see trees growing. There is plenty of air blowing round the peaks and there may be plenty of rain to provide water, but the soil is too shallow for the roots and the weather is too cold in winter for the tree to survive.

Plant habitats then, provide much more than just the essentials for making food and supplying oxygen. They provide suitable weather conditions all year round. Although a plant may survive in its habitat it must be able to do one more thing there. It must be able to breed. When a plant has bred, its seeds are scattered. If the seeds land in a suitable habitat, they will sprout and grow into healthy plants. If you don't find a plant growing in a particular place, it may be because one or more of its needs are missing and the place is not its habitat. The true test of a plant's habitat is to find that the plant is breeding there. Next time you look at a tree, look for its flowers, fruits and seeds. If you find them you will know you are in the tree's habitat, the place where it is truly at home.

How many different kinds of plant habitat are there?
There are many different kinds. Imagine that you are on a beach close to the sea. This is not a habitat for flowering plants. The water is salty and the waves are too strong for any flowering plant to survive there. Now imagine you walk up the beach away from the sea. At the top of the shore you may find sand dunes in which tall spiky tufts of marram grass are growing. Beyond the sand dunes is sandy soil on which plants such as gorse and heathers are growing. This habitat is known as a heath. Once you have crossed the heath, you may enter a wood or see a pond or a lake. All these places - sand dunes, heaths, woods, ponds and lakes are habitats for plants. Some other habitats are marshes and grasslands.

Are the same kind of plants found in each habitat?
Some plants, such as grass, may be able to survive in a few habitats but many plants can only survive in one. For example, a water lily is only found in ponds. It cannot survive in fast-moving water in rivers and cannot grow in the drier habitats on land.

How can one kind of plant survive in a habitat and another kind die?
Each plant has special features, which help it survive in a habitat. These features are called adaptations. For example, the sand dune habitat is very dry yet the marram grass can grow long leaves. You may think that the leaves would lose a large amount of water through their holes but the plant has special adaptations. The holes are not spread out on the underside of the leaf as in most plants. They are in a narrow slit and most of the leaves' surface is covered in wax. The wax prevents the leaves losing water and the holes only lose water very slowly because the air in the slit is full of water vapour.

What are the plants you see growing on a rocky shore?
You find seaweeds growing on a rocky shore. They are not plants. They belong to a group of plant-like living things called algae. These are adapted to living on the shore by having tough bodies, which can stand up to the pounding of the waters. They have strong root-like strands, which hold them securely to the rocks, and have a slimy surface which stops them losing water when the tide is out.

Do algae grow on land?
Yes, some kinds of algae do. They need damp habitats. You may find algae forming green slime on rocks in ponds or rivers. It may be found on damp walls and on the damp parts of a tree trunk.