From the Amazon to the Australian outback, the world’s forests are on fire. But just as all these trees disappear, politicians are sprouting promises to plant more of them like the dawning of a global spring.

In the run-up to the UK election on December 12, Labour says it will plant two billion new trees on British soil by 2040 – that’s 100m a year. The Conservatives are pledged to 30m a year, while the Liberal Democrats say 60m.

Perhaps the strangest efflorescence is Nigel Farage’s promise to persuade Donald Trump to lead a global afforestation campaign.

These tree-planting pledges are certainly a step in the right direction, but there’s a problem. Everything being said is big on rhetoric but light on practicalities. As I know from many years of being involved with mangrove afforestation in the tropics, it’s a lot easier to plant seeds than it is to grow trees. So what lessons does the UK’s next government need to learn before it sends planters all over the countryside?

First, some context. This clamour to plant more trees can be traced back to the Intergovernmental Panel on Climate Change (IPCC)‘s influential – and quietly terrifying – Special Report on Global Warming of 1.5°C of 2018. The report envisages four scenarios to take us to the degraded, unstable, but perhaps not catastrophic, promised land of only 1.5°C warming.

Along with very steep cuts in emissions, all four scenarios require us to remove much more carbon dioxide from the atmosphere than at present. The more that we can do this by protecting and expanding natural carbon sinks, including forests, mangroves, seagrass meadows and peatlands, the less we’ll need to rely on difficult technologies such as carbon capture and storage. This will also make it easier to handle the additional burdens after 2050, by when the report stresses we’ll not only have to be reducing net emissions but overall greenhouse gas concentrations as well.

Problematic planting

So the political parties are certainly right to emphasise trees – and there’s a big prize in our midst. Recent research estimated a spectacular 5 million km² of land that could be afforested, with the potential to increase global forest cover by about 25% to some 50 million km². This would potentially sequester more than 200 billion more tonnes of carbon in the process. Another team of academics has since countered that the 9 million km² estimate may be up to five times too large for various reasons, but everyone at least agrees there’s plenty space for more trees.

Having said that, a lot can go wrong with planting. Take mangrove forests. More than 45% of them have been cleared around the world in recent decades for everything from agriculture to fish farming to tourism to charcoal production. This is an ecological disaster because they are truly extraordinary carbon sinks. At the field site where I have been stationed in Kenya, their waterlogged soils hold more than 1,500 tonnes of carbon per hectare, most of which is vulnerable to oxidation and release if the forests are removed.

For these reasons, there have been numerous large-scale efforts in different countries to restore these trees, but they have often failed. In Sri Lanka, for example, a survey of 23 sites where planting had been attempted showed that in more than half, none of the mangroves survived – and over 50% of seedlings survived in only three sites. In another survey of mangrove replanting across 74 sites in Thailand and the Philippines, only 20% survived.

Such planting projects are often victim to inappropriate targets in which planters are incentivised by numbers of trees or the total area planted, rather than, say, survival rates after one year. Perhaps unsurprisingly, this has led to mass plantings in unsuitable places with no follow-up care.

Yet even before you talk about incentivising planters, you need to address the reasons why trees are not already growing in an area. Assuming the site is ecologically appropriate for the trees in the first place, you need to ensure you have the right social and economic context for them to survive.

To understand what I mean here, Kenya is a good example. This country has a long-term problem with people removing and damaging mangroves, for instance to provide building poles and firewood. People are poor and have few economic alternatives, while the laws protecting the mangroves are not properly enforced by the authorities. This means that if you plant more trees, they’ll just get cut down.

To turn this situation around, international charities and scientists, including me, have been working on a project with local people in the south of the country. It allows donors from around the world to pay locals to maintain and reforest the area as a means of carbon offsetting while helping them develop other income streams that rely on the forest such as beekeeping and ecotourism.

This has helped several villages to flourish, among other things by providing more money for education, clean water and healthcare. Since 2014, the project has seen 10ha of mangroves planted and another 117ha restored and conserved, while paying more than US$60,000 (£45,800) to the community.

The UK situation

This is a small illustration of how reforestation and forest conservation can be effective in sequestering carbon if it has grassroots support. While Kenya might seem a long way from the UK, the same principles apply in both countries. Only 13% of UK land is forest, much lower than many European nations, and a range of land-owning, industrial and agricultural interests work to keep it that way.

Successful afforestation will require negotiating with and sometimes confronting these interests – and we must not permit naïve or cynical proposals to undermine public understanding and trust.

So while we should welcome the UK political parties’ tree-planting commitments, they are only credible if they also address the long-term causes of forest loss as well as setting targets that ensure that planted seedlings actually grow into trees.

We have heard a lot about the magic money tree in recent years, but now there is a danger that the political parties convince themselves of a magic carbon tree. Big eye-catching targets are one thing, but there needs to be a serious discussion about how they will be delivered. Otherwise, this risks being a dangerous waste of time.

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