A matter of leaf and death

Different pigments contained in leaves are responsible for the autumn colours. Picture by Victoria Manley
Autumn colours on the Woodcock Way circular walk in Dalby Forest. Picture by Janet Sanderson

This week I have been captivated by a photograph taken by a member of my Facebook group (Picture That Walk). It shows a handful of fallen leaves, and the array of colours is simply incredible. Another photograph also caught my eye, taken on the Woodcock Way circular walk in Dalby Forest, and again, the autumn colours are just spectacular.

Now the clocks have gone back we feel like we are firmly heading towards winter, which this year officially starts on 21st December and ends 20th March 2023. That period is known as the Astronomical Winter, although the Meteorological Winter starts on 1st December and ends 28th February. The leaves have almost all fallen now, and this year autumn has once again came up trumps, with some fantastic displays that had me marvelling at Mother Nature’s accomplishment. For me, seeing the landscape transform in such a way somewhat softens the blow of summer coming to an end. Although the trees are what we call ‘dying off’, they are not so much dying as ‘going to sleep’, recharging their batteries so that they can burst forth with new life in the spring.

The intensity of the colour and the duration of the display is largely dependent on the behaviour of the weather, with reduced daylight hours and cooler nights triggering the start of the change telling us that autumn is arriving. An ‘indian summer’ with warm, dry days and colder nights usually leads to a long-lasting and more varied and intense colour display, while a drizzly, dank, mild September and October will mean a short-lived burst of colour, before leaves turn brown and fall off the trees.

The colour change is all down to the behaviour of the chemical chlorophyll, which is responsible for the green hues. Chlorophyll is the most dominant pigment and is active in spring and summer, using the sun to transform carbon dioxide and water into nutrient-rich starches and sugars in a process called photosynthesis. Chlorophyll constantly breaks down and replenishes, thanks to the large flat surface of a tree’s leaves which allow them to absorb as much sun as possible.

As we approach autumn, this process slows down, and chlorophyll becomes less dominant, allowing other pigments contained in the leaves to become more visible. There are three categories of chemical, each responsible for certain colours. Flavonoids are yellows, carotenoids are oranges, and anthocyanins are reds and purples and the proportion of these pigments varies from tree to tree, which explains why they differ in colour and shade.

Trees are really very clever, and recognise that they need to shed their leaves to preserve their meagre water and nutrient resources to ensure they can survive the winter. To do this, they grow a layer of cells between the branch and the stem of the leaf which severs the connection between them, causing the leaf to fall off.

That’s not the end of the story though. The leaves that fall surround the base of the tree, trapping in moisture and heat, and they gradually break down, becoming like a compost which in turn is absorbed into the ground, again delivering much needed sustenance into the soil.

We may hate having to rake up fallen leaves, but it isn’t always necessary. If they have fallen onto a flower border, then you may as well leave well alone, as they will act like a warm weed-deterring blanket against the frost, and will also deliver goodness back into the earth as they break down. The same applies if they land on your lawn, just as long as there is not too thick or heavy a covering of them, which can damage the grass.

Having said that, when they collect on pavements and drives leaves are a darn nuisance! No sooner have you swept them up, then the wind comes and scatters them all over again. Opposite my mum’s house there are four sycamore trees that have the really annoying habit of shedding their leaves one after another then sending them straight across the road into my mum’s drive and up to her front door. Why they can’t just all drop their leaves at the same time is a mystery, but probably has something to do with how much exposure the each individual tree has to the elements.

It’s a constant battle between man and leaf. And the leaf usually wins.

Read more at countrymansdaughter.com. Follow me on Twitter @countrymansdaug

This column appeared in the Darlington and Stockton Times on 18th and Ryedale Gazette and Herald on 16th  November 2022

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