At the top of an ancient oak at Knepp estate in East Sussex, a white stork has made a scruffy nest. The birds made headlines in 2020 when, after an absence of centuries in the UK, the first chick hatched. Alongside bison, beavers and white-tailed eagles, the storks are one of many species reintroduced to Britain in recent decades in an effort to restore animals to ecosystems where they had been wiped out. The oak tree, by contrast, has been here continuously for 12,000 years.

But ecologist Charlie Gardner is worried one of them may not have a future here – and it’s the oak. By 2050, London’s weather could resemble that of Barcelona, with long stretches of summer drought. These ancient trees were not designed to thrive in such conditions. “More and more individual trees will die and reproductive success will fall,” says Gardner. Around the world, millions of creatures facing unprecedented temperatures and habitat loss are on the move. The climate crisis is causing a vast array of species – from algae to butterflies, woodlice to birds – to shift northwards. Species are travelling north at a median rate of 17km a decade, according to 2011 research. That average equates to 20cm an hour – two to three times faster than previous estimates.

Some creatures move faster – the comma butterfly, for example, has been travelling north by about 11km a year. But trees are at the other end of the scale. We do not tend to think of them as migratory: unlike insects, birds and mammals, they are slow-growing and rooted to the ground. But forests, too, make slow moves over the course of generations and centuries, as saplings seeded in temperate climates succeed and those in harsher conditions fail. Their problem now is a matter of speed: many trees planted today will not reach maturity for 100 years and the changes caused by the climate emergency are too quick for trees to adjust. Faced with this problem, Gardner is one of a growing number of ecologists and scientists proposing a radical, controversial solution: we help the trees on their march.