Hazy afternoon sunlight filters through the leafy canopy, leaving the air sluggish and warm. It’s a hot, still day and the wood is peaceful, the rumbling of nearby traffic muffled by vegetation. I watch the progress of a speckled wood butterfly as it totters slowly along the path towards me, following a thicket of brambles whose armoured stems are decorated with ripening blackberries.
I’m sitting on a log, holding a yellowing leaf that was cast to the ground by one of the nearby trees. It’s from a field maple; it has five softly rounded lobes that are splayed like chunky fingers around a palm. It’s golden and buttery and has a few brown speckles here and there — a ripening banana skin in leaf form.
But one thing is bothering me. It’s August, not October. The air smells of warm grass, it’s still light at 9pm and the blackbirds haven’t started doing their wintry “plinking” calls yet. Autumn feels like a long way away — but the trees are already changing.
Wimbledon Common, south London. The UK is experiencing its warmest summer on record
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Normally, trees drop their leaves in the winter to avoid damagingly cold temperatures, storing all their resources safely in their roots until the following year. But this time it’s different. Here in the UK, we’re experiencing our warmest summer on record, and the combination of prolonged heat with below-average rain has initiated an ancient, evolutionary survival mechanism built into the DNA of deciduous trees. They aren’t dropping their leaves because the season is changing, they’re doing so because they’re experiencing stress.
Leaves are full of holes to allow carbon dioxide to enter, but in doing so water vapour can escape. When a tree is experiencing drought for a prolonged period of time, it’s genetically programmed to shed its leaves prematurely, effectively blocking up the points at which water is escaping to conserve its supply. This results in a “false autumn”, a phenomenon whereby trees and plants start to behave as if the season has changed, even though it’s still summer.
Looking at trees around the country in your local parks and woodlands, it will be clear that some have been affected more than others. The oaks and ash — species with extensive root systems — still wear their deep, midsummer greens, while more shallow-rooted birches and beeches are yellowing. Some are already looking skeletal and bare. Young trees will be suffering more than older ones, too, unable to access water deeper in the soil without fully grown root systems.
Hardy native species include the sessile oak …
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… the downy birch …
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… and the small-leaved lime
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Trees can handle premature leaf drop from time to time, but when it happens more regularly — as we’re starting to experience with climate breakdown — we will probably see changes in the composition of trees in our streets, parks and woodlands as more drought-tolerant species such as common lime and holly persist in favour of those less able to cope, such as hornbeam and sycamore.
Overall tree health might deteriorate as organisms in the soil — dependent on a steady supply of sugars from the trees through the summer — wane as leaves drop prematurely. Horse chestnuts — our beloved conker trees — might suffer more than most, already under pressure from a small leaf-mining moth that causes early browning and leaf fall. There will be knock-on effects for migrating birds such as chiffchaffs, willow warblers and house martins, too, which depend on the abundance of aphids and other insects associated with tree leaves.
Sitting on my log, I look closely at the yellowing maple leaf. It’s such a beautiful thing, really. Up close I see intricate patterns and colours telling a story of seasonal change. But deep down I feel the twinge of unease. There is beauty, yes, but I worry about what it means for the future. False autumns are becoming more frequent as trees struggle to keep up with the rapid pace of climate change.
Oak in the autumn
MICHAEL ENGLAND/GETTY IMAGES
Moving forward, we need to think about planting a diverse mix of native trees, including hardy species like pedunculate and sessile oaks, rowan, downy birch and small-leaved lime. In their own way, the trees are telling us that something is fundamentally wrong, and it’s important now that we start listening.
Leif Bersweden is the author of Where The Wild Flowers Grow, published by Hodder & Stoughton