Why do trees think it’s autumn already?

Why do trees think it’s autumn already?

Fallen Leaves, North London

The early fall of leaves in London

From the crushing leaves underfoot and the fiery foliage that adorns the trees, you might be thinking that autumn has come early.

But experts say this suggestion of changing seasons is not genuine. Rather, it is the telltale sign of a “false autumn”.

They warn that the heat wave and drought have pushed the trees into survival mode, with leaves falling or changing color as a result of stress.

And some may end up dying as a result.

Tree dying in a London park

Tree dying in a London park

Reddened leaves and early leaf fall are signs that trees are stressed and “closing in store,” says Leigh Hunt, senior horticultural consultant at the Royal Horticultural Society.

“It’s giving the impression that it’s autumn already, but the days are too long for these natural autumn processes to begin,” he says.

“Physiologically, plants are not responding to autumn conditions; that’s why we call it ‘false autumn’.”

Bodmin, Cornwall

Old tree skeletons exposed due to low water levels at Lake Colliford near Bodmin, Cornwall

He says that in all of his 45 years, this is one of the most severe years he has seen in terms of damage to trees in the countryside.

And while established trees can withstand drought through their extensive network of roots, younger specimens, such as those planted in poor soil by roadsides, can wither and die.

‘Second Spring’

Trees that have lost just a few leaves with just a little yellowing should recover with enough rain, he explains.

There is a “critical point”, however, when the tree cannot replace the water lost through the pores of the leaves and “literally dehydrates” or dries up.

In conditions such as those seen recently, trees may react by producing more seeds – for example, acorns – in an attempt to reproduce and survive in the future.

dry soil

Drought has left the soil hard and compacted, which can affect germination

And if there’s a lot of rain, we might even see “a second spring” with the trees giving an extra boost to growth, he says.

early berries

Other signs of unpredictable weather can be seen in berries that appear on plants and bushes.

The Woodland Trust, which tracks seasonal changes, has received its oldest report of ripe blackberries – as of June 28.

He says fruits and nuts are ripening faster than ever, which “could spell disaster for the wildlife” that feed on them.

“The record heat we’ve just experienced has helped bring about a number of early fall events,” says Fritha West of the Woodland Trust.

“We have received some of our first records of ripe blackberries from southern England. Hawthorn and rowan are also maturing early in some parts of the country, where early leaf coloration has also been observed.

“Elderberry and holly have also been recorded as fruiting earlier. Both extreme temperatures and lack of water can cause trees to drop their leaves sooner than we expected.”

shrinking rivers

The long-term consequences of the drought are difficult to predict, but ecology experts believe that weeks of dry grasslands and rock-hard soil in much of southern England will have a big impact on wildlife.

American crayfish shell

A crayfish shell on the dry bed of the River Thames in Ashton Keyne

In and around rivers, drought could be felt for years to come.

During summer droughts, fast-growing algae can smother wetland plants, killing them by blocking out light.

Reducing river levels reduces the habitat of fish, amphibians and invertebrates, affecting entire ecosystems.

“These plants provide vital habitat for insects and fish, and their loss from the ecosystem causes major changes in the food chain,” says Dr. Mike Bowes, UK Center for Ecology and Hydrology.

“It may take several years for plants to be able to recover or recolonize these stretches of rivers affected by drought, and so the impact of severe droughts can be prolonged.”

Follow Helen on Twitter @hbriggs.

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