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Now we’ve entered the beautiful season of autumn, it's time to welcome the rustic colour changes of the countryside that this special time of year brings. Saying goodbye to summer is tough, but the glorious colours of an autumnal landscape can surely soften the blow.

One of the most fascinating things about autumn is the way the leaves turn from their summer green into hues of yellow, red, orange, gold and brown. While it's a stunning sight to behold, especially when you're out for a rural walk to witness the rich landscape first-hand, do you know the scientific reason behind the colours?

Why are leaves green in summer?

In summer, leaves are various shades of green because of chlorophyll, a group of green pigments. Chlorophyll is essential for producing sugars, such as glucose - a source of energy for plants and a building block for their continued growth.

It is green because it absorbs light from the blue and red portions of the electromagnetic spectrum. The energy the sugar produces draws water from rainfall and carbon dioxide from the air through the plant's roots.

Energy is distributed to the leaves and oxygen is released into the air, using a process known as photosynthesis, which helps to keep the environment healthy for people and animals alike. This is why plants are so vital to the continued survival of the earth.

Why do leaves change colour so quickly in autumn?

As summer ends and darkness falls earlier, with the sun crossing the sky at a lower angle and the air becoming cooler, there isn't sufficient light and warmth for photosynthesis. Even water may be in short supply if the conditions are icy.

Colder temperatures trigger a change in trees and other plants to cease producing chlorophyll and get ready for winter, when they will be deprived of sunlight and food. Deciduous trees shed their leaves to conserve moisture and as they begin to shut down, the veins that convey fluids to the leaves are gradually closed off.

This leads to a process known as abscission - the natural detachment of parts of the plant, such as dead leaves. Other pigments begin to reveal themselves.

Do different tree species go different colours?

Compounds known as anthocyanins are found in large quantities in maples and make the leaves go red, while carotene makes leaves turn yellow. In trees such as oaks, dogwoods and cherries, glucose becomes trapped in the leaves when photosynthesis stops. When the glucose is chemically broken down, it leads to shades of red and purple. The brighter the sunlight, the more anthocyanins are produced, creating a brilliant colour display.

Trees such as the horse chestnut start to turn earlier in the autumn season, when the most vivid autumnal colours are produced. In the early days of autumn, the brightest colours occur on sunny days, followed by cool, dry nights. The amount of anthocyanins increases in dry weather, which produces a greater concentration of sugars in the leaves.

How do trees survive in winter?

If autumn comes as early as mid-September, this is when you can see the most brilliant leaf colours, but continued dry conditions and an absence of frost can prolong the colours in all their vibrancy until late October. If it's a particularly mild autumn, the golden russet hues could continue well into November.

However, a severe frost or storm can bring the colourful landscape to an abrupt end. In most tree species, the leaves finally turn brown just before they are shed. This is the colour of the decaying cells and the waste products in the leaves. This forms leaf litter, which breaks down into the soil, providing nutrients for years to come and feeding soil organisms, worms and fungi.

The tree reabsorbs many of the chlorophyll nutrients, forming a protective layer where the leaf stems meet the branches. Trees can survive through the winter thanks to the sugars they have stored during the summer, using the stored energy to grow the new leaf buds that appear the following spring.

What other autumnal changes take place?

If you were to go for a walk in the countryside, you might notice plenty of other autumnal changes. For example, you can see wildlife you may not spot at any other time of year.

Birds will be flying in from the Arctic and Eastern Europe for a mellower winter. Look out for waders, wildfowl, pink-footed geese, starlings, wheatear, redstart, willow warblers and plenty more.

The red deer mating season takes place in autumn, so they will be about in abundance, after spending the rest of the year in single sex herds. Dominant males round up their herds of females during the annual mating season. The stags often get into fights, antlers clashing, which is one of the most spectacular sights in nature.

If you're lucky, you might see the UK's rare native red squirrel, as they are out foraging nuts to store away for the long winter months.

What are the typical smells and sounds of autumn?

The moment the leaves start changing colour, falling from the trees and lying in ever-growing piles on the ground, you will experience the fresh woodland smell that they bring. The sound of the leaves crunching underfoot is also something forever associated with autumn.

You may also smell a slightly alcoholic aroma if there's any fruit on the ground. It's not an unpleasant smell, it's more rich and sweet, particularly when it emanates from plums, blackberries, apples and pears.

Think of walking through the woods on a crisp autumn afternoon, with a slight breeze rustling through the trees, accompanied by the gentle sound of raindrops as they start to pitter-patter. You will also hear the rather wistful autumnal bird song at dusk.

The famous English Romantic poet John Keats found autumn so moving that he wrote a poem, To Autumn, after taking an autumnal walk near Winchester in September 1819. It has become one of his most famous poems, with its beautiful imagery recognising autumn as being the transitional period after the last days of summer.