This article is part of a guide to London from FT Globetrotter
Usually, the first trees we see turning are the ash trees — especially the American ash, which has such wonderful deep purples and reds. The common ash’s leaves turn yellow at the same time, and they look amazing together. Currently we have good conditions: warm days, cooling off at night, which are ideal for autumn colour.
This year, however, because of the summer’s unusually high temperatures, we are seeing a staggered autumn. We aren’t getting the full blaze of colour all at once. Trees are dealing with the seasons individually, as they all have different drought strategies.
Many trees, including horse chestnuts, walnuts and tulip trees, lost their leaves sooner than usual in a “false autumn” and have already gone into early dormancy for winter. As a result of the summer drought, trees such as these lost too much moisture from their system, and their way of saving energy is to drop their leaves. English oaks, on the other hand, aren’t even starting to go into autumn. They’re still holding on, using these unseasonably warm autumn days to store up energy for hibernation in order to bud next spring.
We will see a high tree-mortality rate in spring, as lots of them don’t have the sugar and stored carbohydrates needed for next year’s growth. Spring is the most stressful time of year for trees, and if they haven’t stored enough energy they might not be able to push out leaves. Little buds will appear, but there will not be enough strength for them to grow further, and the tree dies.
This is the first time in living memory I have seen such grave effects of heat and drought stress. The trees have tried to draw water from the soil, but it just isn’t there. Common beech is my highest-risk tree in the arboretum — it doesn’t like drought. We are currently losing a large number of mature beeches.
At Kew, we are beginning to identify species that will be able to deal with climate stress in the future. Mediterranean trees show more resilience, as do species growing in California, and across the Caucasus too. The holm and chestnut-leafed oak, as well as the Persian ironwood and hornbeam, should all do well. But trees live for 500 years plus — it is hard to predict what conditions will be like so far in the future.
Kevin Martin is head of tree collections at Royal Botanic Gardens, Kew
Where would you recommend to see autumn foliage at its finest in London? Tell us in the comments
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