Plantwatch: when do trees lose their leaves?

Paul Simons
The annual service of remembrance at the Cenotaph, Whitehall, London on 11 November 2017. Photograph: Rick Findler/PA

The annual Remembrance Sunday service was held at the Cenotaph in London more than a week ago, and what caught the headlines was the Queen looking on from a balcony for the first time. Less attention was paid to the London plane trees lining Whitehall, which were still full of green leaves despite recent storms and frosts.

Maybe this seems unremarkable these days, but the trees are an impressive sign of how autumn seems to be coming later in the year, probably thanks in large part to autumns growing warmer.

There are, however, surprisingly few long-running records of autumn in the natural world, although there are many records for spring. Tim Sparks, an ecologist at Coventry University, came up with an ingenious way of looking back at autumn trees over almost 100 years, by searching through old photos and films of Remembrance Sunday at the Cenotaph.

The commemoration service began on 11 November 1919, when it was called Armistice Day, and the difference in the London plane trees compared with modern times is stark. “Those trees in the early days were the same London plane trees as today but were bare of leaves. Now, in the last 20 years, the change has been dramatic, and no Remembrance Sundays in recent years have had skeleton trees in the background,” said Prof Sparks.

A similar phenomenon can be seen in remembrance commemorations in the Champs-Élysées, Paris, which is also lined with London plane trees.

Historical records of trees in autumn are invaluable for helping to reveal how trees and plants are responding to the changing climate, and the wider effects on the natural world.