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| Many bright colours can be seen on the Reserve at this time of year |
The wet summer was not all bad; a bumper crop of leaves on the trees at Attenborough Nature Reserve was the first hint of a glorious autumn. If it was hot and dry, the stress would have caused the trees to shed their bounty long before it could turn golden. It was all down to September now, would the month that herald’s autumn also herald in a season of awe and colour?
The warm start to September was like an extra growing season for the trees and this last spurt of growth ensured there were lots of sugars in the leaves before a seasonal change occurred.
As hours of daylight gradually reduced during September, this triggered a layer of cells, called an abscission layer, to grow at the base of the leaf, effectively cutting it off from the rest of the tree. The countdown to leaf fall had begun, but what colour had not been decided yet?
One consequence of the abscission layer forming is that chlorophyll, the green pigment that gives leaves their characteristic colour, is not produced anymore and gradually disappears from the leaf, allowing other pigments such as xanthophylls (yellow) and carotenoids (orange) to be seen. Lots of sunshine and cool nights hasten the destruction of chlorophyll, thus revealing these other pigments which are less susceptible to low temperatures. During the first half of September high atmospheric pressure brought clear skies both day and night; the solar panels regularly reached generation levels akin to summer and 12 nights recorded temperatures below the average minimum for September of 10.9oC.
If your idea of a perfect autumn includes shades of red and purple, then another pigment, called anthocyanin, is needed. This pigment results from the breakdown of sugars that are left in the leaves after the abscission layer has formed, and put simply, the brighter the light the more anthocyanin is produced during autumn! September had slightly above average sunshine levels, but there are a few flies in the ointment that could dispel any arboreal treat this autumn.
Minima below freezing will stop the leaf from manufacturing anthocyanin, so an early frost is bad news for a colourful display. September was frost free as usual but another factor to consider is wind. Stormy weather can cause the leaves to fall from the trees before they take on their colourful hues. A deep depression did bring 76% of the month’s rain on the 24th but we escaped the worse of the winds and no mass leaf fall was recorded at the Nature Reserve.
If the rest of autumn is sunny and calm, with some cool but not frosty nights, we might witness one of nature’s spectacles, and one you can see on your doorstep.
If you want to enjoy the colours of autumn, Nottinghamshire Wildlife Trust manages some excellent woodland reserves. Please visit www.nottinghamshirewildlife.org/nature-reserves to find out more.
