Category Science

Plant survival

 

 

 

Plants can live almost anywhere. They live in dry deserts. It may not rain there for years. Cactus plants can live in hot deserts. They have thin, sharp leaves, thick skins and long roots. They suck up water from far under the ground.

 

 

 

 

 

 

This is a very large cactus. It stores water in its thick stem.

Deserts can be cold and dry or hot and dry. Plants can live in both hot and cold deserts, but they have to be very tough. They need a way to store water for a long time. They do this by having a thick stem and skin, and thin spikes instead of broad leaves. Thin leaves lose less water than broad leaves.

 

 

 

 

 

 

 

Some plants survive in muddy swamps.

Mangrove trees grow along tropical coasts in salt water. Mangroves have branches which send roots down into the water. Eventually, the stilt – like roots support the leafy tree above the water and hold it safely in place.

 

 

 

 

Seeds survive for a long time in the dry desert.

When rain falls on a hot desert, plants spring to life. Seeds buried in the sand grow into flowering plants. In just a few weeks they can produce seeds and die back. The seeds lie dormant in the ground for many months until the next rains.

 

Trees

 

 

Trees are the biggest plants of all. There are three kinds of trees – palm, evergreen and deciduous trees. The trunk of a tree is covered with bark. You can tell the age of a tree by counting the rings on a tree stump. Some trees can live for 4,000 years!

 

 

 

 

 

 

 

Some trees keep their leaves all year. They are evergreen.

Most pine and fir trees are evergreen. They have cones and are called conifers. Cones are the flowers of the conifer tree. The leaves on conifers are called needles. A few needles drop off every day and new ones grow all year round.

 

 

 

 

Some trees lose all their leaves in autumn.

In autumn, the weather becomes colder and there are fewer hours of sunshine. This makes the leaves of some trees change colour and fall off. Trees that lose all their leaves after they turn brown in the autumn are called deciduous trees. Oak and beech trees are deciduous.

 

 

 

 

Roots grow down to find water.

A tree’s roots can spread wider under the ground than the branches spread above the ground.

 

Trees cutting and moving

 

 

After the trees are cut down they are taken away. Most logs are carried out of the forest on special Lorries or trains. They are taken to a sawmill. At the sawmill, huge saws can quickly cut up large tree trunks.

 

 

 

 

 

 

Animals can be used to pull logs out of the forest.

In some forests, big machines cannot be used. In these places animals, such as horses or elephants, are used to transport logs out of the forest. The animals can easily move between growing trees and do not harm the environment.

 

 

 

 

 

A saw cuts the tree into planks.

At the sawmill the bark is trimmed off and the logs are cut into planks. Logs can be cut in different ways to give different grain patterns. Hardwoods can be cut into thin slices called veneers. Veneers are used to decorate objects.

 

 

 

 

 

 

These planks are drying.

The cut planks cannot be used straight away because they still contain a lot of sap. Sap is the liquid or juice inside the wood. Freshly cut wood is called ‘green’ timber and needs to be dried out so that it will not twist, bend, crack, or shrink when it’s used. Drying the wood is called seasoning.

From seed to timber

 

 

Most of the wood we use is specially grown in large forests. These forests are carefully planned to help the trees grow well. The kinds of trees planted are the ones that will grow best in the forest’s soil and weather.

 

 

 

 

These baby trees are growing in a tree nursery.

Conifer tree seeds are collected from pine cones in the autumn. Before they are planted, the hard seed coats are rubbed with sandpaper to help them grow quickly. The seeds are planted in paper containers and kept in a nursery to protect them from mice, birds and frost. Young trees are called saplings. They stay in the nursery for three years.

 

 

 

 

 

Trees are often planted by hand.

Before saplings are planted out, the soil is prepared with a digger or plough. The trees are planted close together to help protect them from the wind. Sometimes a fence is put up to stop deer or rabbits from nibbling the saplings.

 

 

 

 

 

When trees have grown big enough, they are cut down.

Conifers are cut down when they are 50-70 years old. Broad-leaved trees are left until they are 100-150 years old. Some trees are cut down by a woodcutter, or lumberjack, using a chain saw. Others are cut down with a harvester machine.

 

Wood close up

 

 

 

Each year a tree grows a new layer of wood. The rings inside a tree trunk show each year’s new growth. If you count the rings you can find out how old the tree is. This tree is probably older than you.

 

 

 

 

 

 

Knots show where a branch grew out from the tree trunk.

The fibres make a pattern of lines called the grain. If the lines are close together, the wood is a hardwood. Broad-leaved trees have hardwood which is close-grained. If the lines of the grain are wider apart, the wood is open-grained or softwood. Conifers produce softwood.

 

 

 

 

 

 

 

 

Some wood is very strong.

Trees and other plants make a substance called cellulose. Cellulose forms into strands which mat together and make up the walls of tiny cells inside the tree. The cellulose is very important as it makes wood strong.

 

 

 

 

 

This board game is made from different colour woods.

Each type of tree has different coloured wood. Pine trees have a pale wood and walnut has a dark brown wood. A mixture of different colours of wood is sometimes used to decorate furniture.

Wood from trees

 

The wood we use comes from two types of trees. One type is called broad-leaved trees and the other type is called conifers. Broad-leaved trees grow slowly and have hard wood. Conifers grow much faster and their wood is usually softer.

 

 

 

 

 

 

This oak tree is over 100 years old.

Broad-leaved trees such as oak and maple have wide leaves. Most broad-leaved trees are deciduous, which means they lose their leaves in the autumn. Broad-leaved trees usually grow in mild climates, but some grow in tropical rainforests. Timber from broad-leaved trees is known as hardwood.

 

 

 

 

 

Most of our wood comes from conifers.

Conifer trees have needle-like leaves and grow well in cold conditions. They are grown in large forests called plantations. Plantations are like tree farms. The timber from conifer trees is called softwood.

 

 

 

 

 

Wood from conifers is used to build houses.

Fast growing softwood trees like Scots pine are used to make telegraph poles and the frames for some houses. Timber from slow growing hardwoods, such as oak, is used for making furniture.