Autumn Colours
By Daniel Butler, author and forager
With the equinox just a fortnight ago, nights are palpably getting longer. Autumn is well under way and the leaves are beginning to turn, the greens slowly paling towards yellow. This process happens every year, of course, but the colour range varies widely, dictated by the weather over the summer.
Leaves and needles are beginning to turn in Mid-Wales
(Photo: author's own)
If the various shades of green, yellow, orange and brown and red are starting to be obvious, the chemistry that underpins this is a mystery to most. The process starts with the normal green of a healthy leaf. This comes from the chlorophyll, which is vital not only to the plant, but ultimately to all life on earth. As a photoreceptor, the chlorophyll unlocks the energy in sunlight to convert carbon dioxide and water to sugar and oxygen.
It is produced continually in every leaf throughout the summer, but production starts to decline in autumn as temperatures drop and day lengths reduce. This makes the naturally-occurring carotenes which have also been lurking in the plant tissue become more apparent. As their name suggests, these are a deep yellow, so the leaf turns first yellow, then orange and finally brown.
Autumn colours can be particularly striking when anthocyanins are involved
(Photo: author's own)
For most trees this is the limit of the chemistry, but some also create high levels of red pigments called anthocyanins. These occur when sunlight reacts with sugars inside the leaf. The process is most commonly encountered on apples where the skin facing the sun turns red, but remains green in the shade. Most famously, however, it creates the spectacular reds of New England’s fall, when the fine Autumn weather hits the sweet-sapped maples.
The last really spectacular display was 2020. This was the product of the abnormally hot and dry weather of the ‘Covid Summer’. This produced very high sugar levels and a warm dry autumn exacerbated the rich russets and scarlets.
Colours are muted this year
(Photo: author's own)
This year everything seems very muted in contrast. The long, cool, damp summer has clearly not been great for many trees. There are far fewer wild apples and acorns than normal and the woodland fungi are almost absent in comparison to the usual bounty. On the other hand, it has been a good year for brambles with blackberries fruiting in abundance and, as covered in my last blog, there is a spectacular abundance of rowan berries.