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View of the Lake and Autumn forest park in Heywood Gardens, Co Laois, Ireland. Alamy Stock Photo
Falling slowly
Why are the leaves staying on the trees so long this autumn?
It may look pretty but milder autumns are “causing havoc” in the natural world.
HAVE YOU NOTICED that there are still a lot of leaves on the trees?
Colourful displays of autumn foliage are still sticking around in woodlands around the country.
If follows a warmer-than-average autumn and comes in the context of ongoing disruption caused by climate change which is leading to a lengthening summer and autumn.
According to Met Éireann’s climate statement for October, the month was warmer than average. The national mean air temperature for the month was over eleven degrees and highest temperatures of 19.7 degrees were reached three times.
Those milder conditions have continued over recent weeks – although forecasters are predicting a change to more wintry weather in the coming days.
Speaking to The Journal, Dr Colin Kelleher of the National Botanic Gardens said that as a result of the longer autumns, the colour of foliage may also be changing – with more red and dark colours visible.
The colour change is because warmer summers produce more sugars in leaves, which triggers the production of red pigments.
The taxonomist, whose work focuses on the development and application of molecular markers in plants, said the changes to the climate had been “causing havoc” in the natural world.
Kelleher explained that trees use changes in light or temperature as cues to drop their leaves in autumn or develop new buds in spring.
“Plants don’t know what to do,” he said – and as a result the leaves are staying on the trees later.
The lack of cold nights in particular has prevented leaves degrading on deciduous trees.
“We haven’t had very much cold really that’s why autumn dragged on. If we have a warm October plants wont go into hibernation.”
Dr Kelleher said that it’s now cold enough now for the remaining leaves to drop off, but it’s quite late for them to be doing so.
Cold weather is very important for plant cycles in Ireland as trees need a certain amount of colder days to precipitate bud burst and new growth in the spring.
Essentially “it’s a problem if the leaves don’t leave”.
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