Can trees save the planet?

By Cara Waudby Tolley | June 27, 2022

For years, we’ve been told that trees slow climate change, but there’s more to it than simply planting them, finds Laura Silverman.

As the Chinese proverb goes, ‘the best time to plant a tree is 20 years ago. The second-best time is now’. Trees provide homes and food for three-quarters of the world’s wildlife and plants. They ease flooding. They reduce stress. They give us timber. And they soak up carbon dioxide, a major cause of rising global temperatures. It’s obvious that we need more of them. Fast.

Seeds are being sown across the country. A snapshot of the current scene takes in Plant Britain, a Countryfile project to plant 750,000 trees by the end of 2022, the Big Climate Fightback, a Woodland Trust scheme aiming for 50 million trees by 2025, and plans by the National Trust for 20 million trees by 2030. These should help meet the government target to plant 30,000 hectares of trees a year by 2025. Average tree cover in Britain is just 13 per cent, far below the European average of 35 per cent. Worldwide, we’re losing an area twice the size of Wales every year.

Grand plans

But before you grab a spade, you might like to have the recent report from Kew and Botanic Gardens Conservation International (BGCI) to hand. The paper, published in the journal Global Change Biology, reviewed the effects of forests planted around the world and has highlighted projects that have resulted in carbon being released into the atmosphere, species being lost and the local way of life destroyed.

“When people plant the wrong trees in the wrong place,” says Dr Kate Hardwick, a lead author and Kew’s Conservation Partnership Coordinator, “it can cause more damage… failing to help people or nature.” It’s not just far-flung projects in Chile or South Africa that have caused concern. The UK is still recovering after bogs in the Flow Country in Scotland were drained in the 70s and 80s to make way for fast-growing conifers. “It was hugely damaging because the land was good for carbon capture and as a habitat in its own right,” says John Tucker, Director of Woodland Outreach at the Woodland Trust. “We do need more trees for carbon, but I’m nervous that if we rush into planting them, we’re going to repeat those mistakes.” To help, Kew and BGCI have devised ‘10 golden rules for restoring forests’. Many apply to a lone tree in your garden.

Golden rules

It might not sing with novelty, but the best thing we can do is preserve our current trees because they have already developed complex structures and provide homes for a huge range of species. They will have evolved, say the researchers, to be resilient to storms and floods (both of which are threats from climate change). The big debate in the UK is over ancient woodland, half of which has disappeared in the past century. More than 100 woodlands are at risk from high-speed railway HS2.

If you’re planting a new forest, planning is key. “You need to leave yourself 18 months to two years for the planning and site assessment,” says Tucker. “You can’t just stick a tree in the ground.” You don’t need quite as much patience for a garden project, although other considerations still apply.

You’re free to plant trees in your own garden, unless you’re thinking of a forest of more than two hectares (in England), when you’ll need an Environmental Impact Assessment from the Forestry Commission. If you’re looking at nearby wasteland or a park, you’ll need permission from the owner (possibly the local council). Finding the right area is vital, as shown by the Flow Country conifers. The researchers put ‘previously forested land’ at the top of the list, stressing the importance of avoiding grasslands, wetlands and, further afield, savannahs.

The Wildlife Trusts is campaigning to protect our peatlands, which capture three times as much carbon as woodlands, provide a home for sphagnum moss and large heath butterflies, as well as being essential feeding sites for wading birds.

Choosing suitable trees is also a big factor, applying as much to your garden as to a new forest. Clay soil? Go for birch or crab apple. Damp soil? Try poplar or willow. Oaks are versatile, but you’ll need space for their roots and height. An oak outside the back door could meddle with house foundations, electricity cables and your relationship with the neighbours. An apple or rowan tree, both more compact, might be better. See what flourishes in other gardens and your local area.

You should also consider the advantages of particular trees. “Don’t plant a woodland or a tree just for carbon,” says Tucker, who has a wild mulberry tree in his garden for fruit and a winter cherry for colour. “For me, carbon is an added benefit.” Carbon capture is important, but you’re more likely to care for the tree if you benefit from something immediate and tangible. The paper drew similar conclusions looking at how rainforests could benefit indigenous communities.

Grow local

For forests, the Kew and BGCI researchers encourage a mix of trees typical of ones in the area, including rare and endangered species. These will cope better with the climate and disease and help biodiversity. Native trees are almost always best. “You have to be careful with new introductions,” says Tucker. “Stick to seeds and saplings from the UK.” Exotic species could also become invasive.

“Robinia pseudoacacia, native to North America, is talked about a lot over here. It’s great for timber, but it can spread and become a nuisance.” The researchers cite a similar case in South Africa, where Australian acacias, introduced for wood, have taken over heathlands and lowered the water table.

Planting a combination of species could also prevent disease wiping out an entire patch. Ash dieback threatens up to 95 per cent of the UK’s ash trees, while Dutch elm disease has killed millions of our elm trees over the past 40 years. Brynau Wood in South Wales, a Woodland Trust project which will eventually comprise 150,000 native species, from oak and beech to rare small-leaved limes, is a great native mix. Barn owls, Daubenton’s bats and walkers should love it for centuries to come, while we will all benefit from its ability to absorb carbon.

“Our paper doesn’t set out to say that tree planting is wrong,” concludes Professor Alexandre Antonelli, senior author of the paper and Kew’s Director of Science. “[Tree planting] is a brilliant solution to tackle global warming and protect biodiversity… We just want to challenge the way we plant trees… and herald a new era for the world’s forests that benefits everyone.”

So yes, plant trees, just think before you do it.