Dear Readers, as I was walking along East Finchley High Road today, I was gently walloped on the head by a chunk of bark from one of our magnificent London Plane trees. And not for the first time! Marcel Proust wrote a whole series of novels based on the flavour of a madeleine that took him back to his childhood, but for me, a piece of bark took me back to 2018, another hot dry summer. This was when I first noticed that the Plane trees were shedding a lot of bark, so much so that some of them looked white, and the same thing is happening this year.

High Road Plane tree this year

It turns out that this is a known phenomenon. What happens is that the trunk of the tree, which conducts water to the leaves, actually shrinks during drought conditions, such as those in 2018 and potentially this year. This loosens the outer layer of bark, which then falls. London Planes lose bark regularly anyway (and this is thought to be a reaction to pollution, and a protection against fungi/parasites), but this is independent of the drought-induced bark shedding.

A study in Mainz was conducted during the drought of 2018, to see if the location of 349 London Plane trees affected the amount of bark loss. The trees were measured for location, the impermeability of the soil round about, and various other measures. It was expected that the most urban trees would have the worst bark loss, but this turned out not to be so – trees were affected not so much by the lack of water, as by the temperature. This is an uncomfortable finding, because it suggests that no amount of watering/improving soil permability will improve the outcome for the trees – climate change and increasing temperature is the main cause of the bark loss, and it appears to be this that causes the shrinkage in the trunk, rather than the lack of water on its own.

Bark loss on its own won’t kill a London Plane, but it is an indicator of stress. This might make the tree more vulnerable to fungi, viruses or insects like the Plane Lace Bug.

Whenever I walk under the Plane trees en route to East Finchley Station, I am always so grateful to them for the shade that they provide. You can feel the drop in temperature as you enter their shadow. Let’s hope that their famous resilience to urban stressors will be great enough to encompass even the challenge of our increasingly long, hot summers.

London Plane tree in Temple Gardens, probably planted in 1770