‘False autumn’: stressed trees drop leaves early after scorching English summer

A birch tree in Wisley garden, Surrey. The white branches would normally be covered in yellow leaves in mid-October. Photograph: Martin Godwin/The Guardian View image in fullscreen A birch tree in Wisley garden, Surrey. The white branches would normally be covered in yellow leaves in mid-October. After the hottest summer on record, the tree has dropped its canopy early, stressed from months of high temperatures and choosing to not lose any more water through its leaves. This is also known as a “false autumn”, where the stress of extreme summer conditions prompts trees and plants to behave as if the season has changed. View image in fullscreen Guy Barter, the chief horticulturalist at the RHS, at Wisley garden. Photograph: Martin Godwin/The GuardianThe birch illustrates how extreme weather driven ’s seasons. Thousands of plant varieties at Wisley are still displaying vibrant hues, but the drought-sensitive, yellow-leafed trees such as birches, beeches and sycamores had shed their foliage by mid-October. Normally, autumn’s effect on trees is triggered , dropping night-time temperatures and adequate ground moisture brought on by rain. But severe summer heat and drought has disrupted this usual cycle , resulting in a display that kicked in earlier than expected. The majority of England and Wales remains in drought, and six areas of England were declared in severe drought this month with river and reservoir levels running low. View image in fullscreen Barter beside an oak tree – a species that has fared better than some during the extreme heat owing to its deep roots. Photograph: Martin Godwin/The GuardianUnlike deep-rooted species such as oaks, trees with shallow root systems are unable to tap into deeper groundwater, making them vulnerable to leaf drop when surface soil dries out during a drought. “Birch, beech and sycamore have been among the trees worst affected,” says Barter. “It’s at least as colourful as it is most years, but some of the trees are not giving their best, so it’s not the perfect autumn colour.” The RHS expects an earlier autumn colour peak in drought-hit areas, with intense but potentially fleeting displays. Reds, ambers and purples could stand out as some trees normally prized for yellow foliage lose their leaves. Tim Upson, the director of gardens and horticulture at the RHS, says the colour peak historically comes toward the end of October, but this year’s drought has brought some trees into colour earlier. “Quite often now it’s going into November when you get that crescendo,” he says. “So for me, this is quite unusual.” As Storm Austen blows in, the Met Office has warned of strong winds that could damage buildings and bring down trees.