On day 138 of 365 Days Wild I spent some time looking at the leaves that are now falling from the trees in increasingly great numbers. Yellows, oranges, browns, and even a few reds are beginning to dominate the trees, cover the lanes and footpaths, and fill the gutters.
I thought I’d have a little look into just what exactly causes the different colours that we can see in deciduous trees in Autumn. Here’s what I’ve found out.
Throughout the summer months the trees are dominated by the green of leaves filled with chlorophyll. This biomolecule allows the plant to use the energy from sunlight to convert water and carbon dioxide into sugars for food. The chlorophylls are broken down in the conversion process, but during the growing season are continually replenished, maintaining both the supply of chlorophyll and the green colouring of the leaves. As the days grow shorter and colder, however, the chlorophyll is broken down into cloudless compounds and are not replaced, allowing other colours to show through. Yellow shades are caused by xanthophyll pigments, whilst orange ones are from carotenoids. These pigments are present in the leaves throughout the summer, they’re just hidden by the chlorophyll greens.
Many autumns in the UK yellows and oranges (and brown once all of the pigments have faded) are all we’ll see. This is because the red and purple shades of the most spectacular displays of autumnal colour are caused by anthocyanins, a group of pigments that are not present earlier in the year but are instead produced towards the end of the summer from the breakdown of the sugars produced by chlorophyll. Anthocyanins production relies on bright days and chilly, but not freezing, nights, as well as the presence of high-level of sugars from a dry summer. Only 10% of trees in most temperate regions produce anthocyanins, including maples and oaks, dogwoods, cherry trees and persimmoms. In New England, on the other hand, with its high number of maples, 70% of the trees produce anthrocyanins, which makes for its famous fall displays of colour.
If you’d like to know more about the changing coloura of leaves, you could check out some of these pages:
That’s all for today. What signs of the changing seasons are happening where you are?