The photographs on this post are no longer available.
As the woodland air turns crisp and the Autumn draws in, it is time to view one of Nature’s most beautiful spectacles.
Have you ever wondered why the leaves turn and change colour? Well, here’s a handy little explanation.
We live in a temperate region of the World, where temperatures change and we experience the full range of seasons. In the Winter, the delicate leaves of deciduous trees can’t survive and photosynthesise to produce food for the tree, so preparation for the cold begins. All useful products are taken back from the leaves before they fall to the ground. This preparation is what gives us the beautiful show of colours.
So why do leaves change colour whilst still on the tree?
During the Summer months, most leaves are varying shades of green. They contain a special pigment called chlorophyll, which is what allows the plant to make its own food. As the Autumn sets in and light levels and temperatures begin to drop, these chlorophyll molecules begin to break down into smaller pieces and useful nutrients, like nitrogen, can be reused by the tree. Also at this point, all useful carbohydrates are being returned to the branches and no new minerals or nutrients are brought into the leaf.
All about the Colours
Green chlorophyll is a very strong pigment which masks any other pigments in the leaf. As the green breaks down, other colours are allowed to come through. These colours include yellows and oranges from carotenoids (such as xanthophyll in yellow corn on the cob and carotenes in carrots) and darker colours such as reds and browns from anthocyanins (present in blueberries and cherries). When conditions are bright and cold, the leaf is about to be cut off from the branch and the trapped molecules of sugar promote formation of the anthocyanin, which is used for plant defence, turning the leaf red.
The Rainbow of Autumn Colour
Leaves don’t just come in green, yellow and red, they are a rich variety of browns, golds, bronzes, golden and acidic yellows, purple-reds, tans, crimson and orange reds. The tones and shades are all there because of the cocktail of chlorophyll and anthocyanins. Different proportions produce different colour combinations! For an orange leaf it takes anthocyanins mixed with carotenoids, for brown leaves, a combination of anthocyanin and chlorophyll. Each leaf is uniquely coloured which makes this natural process so stunningly beautiful to witness.
Is the colour change always the same? No, because early frosts can weaken the colours, destroying the anthocyanins that produce the brightest reds. Droughts can cause leaf fall before any colour change at all! Where a few tree species exist in a woodland or forest, colour displays are short but intense. Think of New England and Northeast Asia. More diverse vegetation gives a longer display. Cloudy and warm Autumns, like in mainland Europe, can produce dull colours.
Why is Autumn often called “The Fall”?
Where the stem of the leaf had previously attached to the branch, a closed scar is formed by a new layer of cells. The leaf is then free to fall, usually when the weather conditions become more windy or rainy. Eventually, all of the leaves will have fallen to the ground. Finally, once the leaves die and the final photosynthesising cells (chloroplasts) are broken down completely, leaves turn a very dull and boring brown. It isn’t all bad news though, as these brown and crispy leaves are what make a walk in the woods so satisfying in late Autumn and early Winter. Of course we are rewarded by that special fragrance, rustle and crunch!
Who knew there was so much science going on in the humble woodland here at Saltwells?
Comments