Dear Readers, long before the time when Trick or Treating became such a big deal in the UK, the big autumn festival was Guy Fawkes Night on 5th November. When I was a child, you could buy tiny fireworks for a couple of pennies each. They had names like ‘Traffic Lights’ and ‘Vesuvius’ and each one would last for about thirty seconds before puttering to a smokey end Our back garden was minuscule, and so my Dad was master of ceremonies for the evening. To start with, he’d light one firework at a time, and we’d stand and watch from the kitchen window. Catherine Wheels were always exciting Dad would nail them to the post that held the washing line, and my brother and I would scream with delight if it fell off and careered across the yard, sometimes trapping Dad in our outside toilet until it stopped sparking and sputtered to a halt. The evening usually ended with Dad standing in the rain, lighting four or five fireworks at once and then ducking back into the toilet to escape the miniature inferno. I can still see him, raindrops dripping from the rim of his trilby, sometimes with a cigarette in his mouth, as he tried to get to the end of the seemingly interminable array of incendiaries we’d managed to buy with our meagre half-crown a week pocket money. That’s love for you.

For some reason, this year as I’ve watched the approach of autumn, I’ve been reminded of the fireworks of my childhood. Gradually the trees light up, one at a time. An otherwise green tree might have the smallest hint of orange one day, and yet by the end of the week it’s aglow. It starts so gently that you might almost think you were still in late August and then, suddenly, there is colour everywhere.

Different colours appear in the leaves for different reasons. As the temperatures fall and the daylight hours lessen, a tree is no longer able to collect enough sunlight for growth. Furthermore,  a tree with its leaves still attached is more likely to be pulled over by the wind, and leaves also cause water loss during a season when much of the water needed by the plant is frozen. Therefore, deciduous trees fall into dormancy during the winter. The leaves, which harvested the sunlight and turned it into food, no longer have enough hours of daylight to sustain themselves.The main chemical which helped the plant to photosynthesise, chlorophyll, is what makes the leaves look green. When this ceases to be produced, the other orange and yellow pigments, normally masked by the green colour, can be seen. These pigments are beta-carotenoids, the same chemicals that make egg yolks yellow and carrots orange, and in some plants these are the dominant pigments all year round – think of some alders and Japanese maples, for example. At the same time as the colour change occurs, a layer of corky cells grow in the stem of each leaf, which causes abscission – the process by which the leaf detaches from the tree.

Red pigments are a different story. These are not hidden by the green pigments of summer, but are produced by the tree when about half of its chlorophyll has been used up. The pigments are called anthocyanins, and they are related to the breakdown of the sugars that the plants need. We can also find these pigments in cranberries, cherries and other fruits. Bright, cold days and chilly, but not freezing nights are thought to encourage the production of these scarlet and purple pigments. In most forests only 10% of the trees contain these pigments to any extent, but in New England and in parts of Canada up to 70% of the trees are full of anthocyanins – maples, sweetgums, dogwoods and oaks are amongst the species which can put on a spectacular show. Where present, these pigments can combine with the newly exposed yellows and oranges of the beta-carotenoids to produce a show of such unworldly beauty that it feels as if you are walking through a hallucinated landscape.

Autumn 2012 at Lake of Bays, Ontario, Canada

And when all this is past, we are left with the dead leaves of autumn, a pleasure in themselves as we scuff and rustle through them. The brown and copper shades that are left when everything else has faded are the true colour of the cell walls once everything else has past.

And after that? On the pavements you might see the ghosts of leaves, the shadow-outline that gradually fades like the after-image of the chrysanthemum burst of a Roman Candle. Winter is nearly upon us, but the trees are not going quietly. Just like the night that my dad accidentally set fire to a whole box of fireworks, the trees are putting on an exuberant final show, an over-the-top display of colour as if to make up for the dark, cold, wet nights to come. Let’s take a deep breath of chilly late October air, and enjoy the last great tree-show of the year.