Brought to you by Newscorp Australia

Why do leaves change colour and fall in autumn?

Donna Coutts, March 9, 2020 7:45AM Kids News

Print Article

Sarah and Charlotte enjoying the first falling autumn leaves in Macedon, Victoria. Picture: Jay Town media_cameraSarah and Charlotte enjoying the first falling autumn leaves in Macedon, Victoria. Picture: Jay Town

explainers

Reading level: green

Each autumn, thousands of tourists flock to a few special towns across Australia to look at millions of colourful leaves.

There are so many thousands of leaf-looking tourists, councils organise extra parking, parking attendants, coffee vans and portable toilets. It can be chaotic*!

Why do leaves change colour and fall in autumn?

We wondered too, so we did some research and raked up a pile of fascinating facts.

WHY DO TREES LOSE THEIR LEAVES IN AUTUMN?
Trees that lose their leaves in just a few weeks over autumn are called deciduous trees. These are more common in colder parts of the world – mostly in the northern hemisphere* — where the winters are freezing and there’s a lot of snow.

Losing leaves is a way of preparing to survive the winter. If the leaves stayed on a tree, temperatures a long way below zero could freeze the leaves (which would wreck them and then they’d fall off anyway) and a build up on the leaves of snow or ice, which weighs a lot, could break the tree’s branches.

Colorful Autumn Season and Mountain Fuji with morning fog and red leaves at lake Kawaguchiko is one of the best places in Japan media_cameraMt Fuji, Japan, in autumn. Many trees in very cold places lose their leaves before winter to save up nutrients and minimise damage from ice and snow. Picture: iStock

WHY DO LEAVES CHANGE COLOUR?
This is the tree’s way of saving up nutrients* for next spring and summer. It’s much more efficient than letting a whole lot of goodness fall to the ground.

Plants grow by taking in sunlight through their leaves, plus water and nutrients from the soil.

The leaves capture the sunlight with a natural chemical called chlorophyll, which makes the leaves green. Chlorophyll turns sunlight into tree food through a process called photosynthesis.

In summer, when it is very sunny and warm, plants photosynthesise a lot.

When autumn comes, with shorter, cooler days, deciduous trees know it’s time to prepare for winter. A deciduous tree breaks down the chlorophyll in the leaves and sends the nutrients down to the roots to be stored underground until things hot up again.

When chlorophyll is broken down in the leaf, the green colour disappears. The colours we can see in autumn are from what is left behind in the leaf and this ranges from yellow to orange to red, maroon and brown. One type of natural chemicals left are carotenoids, which is what makes carrots orange.

Autumn is coming media_cameraThe first of the autumn leaves are starting to change colour in Honour Avenue, Macedon, Victoria. The trees in the background will change colour over a few weeks. Picture: Jay Town

DO ALL TREES LOSE THEIR LEAVES IN AUTUMN?
No. If trees aren’t deciduous, they’re evergreen, which means they always have leaves and only lose old leaves gradually across the year. Evergreens are either from places where the winter isn’t harsh or their leaves are adapted to suit a lot of cold weather and snow. Pine trees — the fine, tough needles are the leaves — are an example of this adaptation.

Almost all Australia’s native trees are evergreen. Eucalypts, for instance, are evergreen trees.

Most of the beautiful autumn leaves you see around parks and gardens in Australia are on trees that are not natives.

media_cameraA young koala eating eucalypt leaves.

DO ANY NATIVE AUSTRALIAN TREES LOSE THEIR LEAVES IN AUTUMN?
Australia’s only native deciduous trees are called southern beeches. There are three species, called Nothofagus cunninghamii, gunnii and moorei. They grow in cool rainforests in Tasmania and southern Victoria.

media_cameraNothofagus at Tarn Shelf in Mt Field National Park, Tasmania.

AUTUMN HOT SPOTS
If you live in or visit cooler areas of Australia with high rainfall, you should be able to spot some deciduous trees with beautiful autumn leaves.

Popular tourist hot spots include the Adelaide Hills in South Australia, Macedon Ranges, Dandenong Ranges and the High Country in Victoria, Southern Highlands and the town of Orange in New South Wales, Mt Tamborine in Queensland and across much of Tasmania.

HOW MANY LEAVES DOES A TREE HAVE?
It is impossible to give an accurate answer to this question unless you counted every single leaf on a tree as it fell.

People who love maths love trying to figure out ways to calculate a fairly accurate answer without counting all the leaves.

One calculation we found worked out that a maple tree about as tall as an adult had about 400 leaves on it.

Big trees could have several hundred thousand leaves on them.

media_cameraA big, mature deciduous tree could have hundreds of thousands of leaves, almost all of which fall in autumn. Some people like to rake up the leaves and others leave them to compost where they fall.

GLOSSARY

  • chaotic: in a state of complete confusion
  • hemisphere: half of the world either north or south of the equator
  • nutrients: substances that nourish living things

EXTRA READING

Why is the sky blue?

Secret ‘dinosaur tree’ experiment a success

Amazon fires: who will help save the rainforest?

Women trapped in mountain of ‘cornflake’ algae

QUICK QUIZ

  1. What are two reasons why trees lose their leaves in autumn?
  2. What makes leaves look green?
  3. Are eucalypts deciduous or evergreen?
  4. Where do Nothofagus cunninghamii, gunnii and moorei live and what are they?
  5. How many leaves does a tree have?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Write a conversation
Write a conversation between an adult southern beech tree and a baby southern beech tree. The younger tree is experiencing autumn for the first time and is scared of what is happening to it. The adult tree tries to comfort the younger tree and explains the process so that it is not so scared. What questions might the younger tree ask? How could the adult explain the process in a way that the younger tree understands and makes it sound exciting?

If you have time, you might like to turn this ‘conversation’ into a picture storybook that helps explain the process of leaves changing colour to younger audiences.

Time: allow 30 minutes to complete this activity
Curriculum Links: English, Science, Critical and Creative thinking

2. Extension
The article states that thousands of tourists visit autumn leaf hot spots to see the amazing colours of the leaves. You have just been given the job of managing one of these ‘hot spots’ and advertising the experience to encourage people to visit the area and enjoy the autumn leaf spectacle.

Create a one-page newspaper advertisement for a day out to your autumn leaf hotspot. Some are mentioned in the article but you might know of another place more local to you. Include what people can expect to see. What activities they can do there? Come up with a few activities that could be fun with the leaves. For example: leaf castle competitions, creating leaf mazes for others to follow, autumn leaf artwork. The possibilities are endless. Make suggestions of what people should wear, what they should bring, what facilities are available etc. Present your brochure in a visually appealing way.

Time: allow 45 minutes to complete this activity
Curriculum Links: English, The Arts – Visual Arts, Media, Critical and Creative thinking

VCOP ACTIVITY
With a partner see if you can identify all the doing words/verbs in this text. Highlight them in yellow and then make a list of them all down your page. Now see if you and your partner can come up with a synonym for the chosen verb. Make sure it still makes sense in the context it was taken from.

Try to replace some of the original verbs with your synonyms and discuss if any are better and why.

HAVE YOUR SAY: What colour are the leaves on the trees around you? What other questions like this would you like answered by Kids News?
No one-word answers. Use full sentences to explain your thinking. No comments will be published until approved by editors.

Extra Reading in explainers