English oaks can withstand warming – but other trees will struggle

The English oak tree looks set to become a cornerstone of future reforestation projects and timber plantations in Europe, as one of the only native species flexible enough to survive the rapid climate change expected over the next century.

European forests are a mix of tree species, which have all been able to withstand the climatic variability of their location for hundreds of years.

But climate change means trees planted today, for example for reforestation or timber plantations, must be able to withstand both current conditions and those of a warmer world in 2100.

Johannes Wessely at the University of Vienna, Austria, and his colleagues examined 69 of the most common European tree species to assess how well they will cope with this challenge.

The English oak (Quercus robur) was one of the only species assessed as being fit to thrive under current and future conditions across many regions, says Wessely. Importantly, the English oak “has a high importance for timber production, carbon storage and biodiversity”, he says, making it suitable for all kinds of reforestation projects across Europe.

But many other well-known species, such as the European beech (Fagus sylvatica), will struggle. Many sites where European beeches can be planted and will thrive today will become unsuitable later in the century, but regions that could support the beech later this century are climatically unsuitable today, the study found.

Overall, the average number of tree species per square kilometre able to survive continuously to 2100 could drop by between one-third and a half, the researchers found, depending on how quickly climate change advances.

It means some European forests could be made up of only a small pool of tree species, lacking the diversity and resilience of mixed forests.

Wessely says the findings mean “we should be very cautious about what we plant today, as it will shape our future forests and their future”.

He suggests conservationists may even need to replant forested sites with fresh species later in the century to help woodlands thrive to 2100 and beyond.

“We’re heading into a period of unprecedented changes to the climate,” says Andy Allen at the Woodland Trust, a UK charity. “As the paper acknowledges, we don’t know enough about how existing native species will adapt.”

However, he points out that the study doesn’t take into account trees’ potential to genetically adapt to changing climate conditions. “We do know that UK native trees have very high genetic variability (largely thanks to the majority being wind pollinated, and to the varied geography of the UK) and, therefore, their genetic potential to adapt to change is high.”