Tree-planting has become a cornerstone of many environmental campaigns in recent years. The call to plant trees is everywhere, seen as a simple and effective way to help reduce the impact of carbon emissions and restore natural ecosystems. 

Perhaps the most ambitious example is the 1 trillion trees campaign launched by the World Economic Forum in Davos in January 2020 in support of the UN’s Decade of Ecosystem Restoration, which aims to restore, protect, or plant 1 trillion trees by 2030. That followed a similar campaign aiming to plant 1 trillion trees by 2050 which was kicked off in 2018 by nature nonprofits including WWF. 

This year Brits have been encouraged to join a nationwide tree planting effort in honour of the Queen’s Platinum Jubilee. 

Redditors have even got in on the act when in 2019, when they created a flood of memes encouraging prominent YouTuber Mr Beast to plant 20 million trees to celebrate hitting 20 million subscribers. Mr Beast, real name Jimmy Donaldson, accepted the challenge, started a fundraiser, and teamed up with the tree conservation charity the Arbour Day Foundation to help smash the target. 

But why is there such a big emphasis on tree-planting to curb the climate crisis? And can the humble tree really save the world? 

The 3 Biggest Things You Should Know About Tree Planting

• Trees are the ultimate carbon storage machines — 400 tons of carbon can be locked into just one hectare.
• Restoring a forest the size of the US would store 205 billion tons of carbon — two-thirds of the 300bn tons emmitted since the industrial revolution.
• Tree planting initiatives must be well-researched and planned —bad programmes will do more harm than good.

How trees work 

Trees are the ultimate carbon storage machines. Like all plants, they take carbon dioxide from the atmosphere for their own growth and energy, a process called photosynthesis. They produce oxygen which we breathe as a byproduct of this process. 

Woodlands and forests can lock up carbon for centuries – which is something humans and the planet desperately need them for, given the damage done to the atmosphere by carbon-emitting human activity. 

According to the Woodland Trust, a UK conservation charity, 400 tons of carbon can be locked into one hectare (which is 10,000 square metres — or about two and half football pitches) of woodland alone. 

It follows then that cutting down trees has serious consequences for carbon emissions. A 2018 study found that in Oregon, US, logging had been responsible for releasing 33 million tons of carbon dioxide each year since 2000, dwarfing other sources of carbon emissions such as transportation in the state. 

All trees store carbon but it’s thought that tropical rainforests are even more useful when it comes to defending against climate change. They grow rapidly and produce rainforest cloud cover that reflects the sun rays back into space, according to the Rainforest Alliance. They are also vital for the weather system – helping to create rain through the water vapour transpiring from their leaves which in turns helps prevent droughts in the region. 

Estimates for the amount of carbon in the atmosphere that the Amazon rainforest has stored vary hugely. But whatever the figure, studies have shown that it has helped to mitigate the carbon emissions produced by all the nations in its surrounding area. 

For all of these reasons, climate scientists have hailed the benefits of planting trees and protecting the trees that we already have. 

A huge study from ETZ Zurich University, published in 2019, concluded that by restoring a very large area of forest globally, equivalent to the size of the US, it would store 205 billion tons of carbon. That’s about two thirds of the 300 billion tons that has been released into the atmosphere as a result of human activity since the industrial revolution, the study found. 

Professor Thomas Crowther, who led the study, said that the results were “mind-blowing.”

He said: “We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be…But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage.” 

How humans are damaging the role trees can play

However, both global warming and deforestation pose a huge threat to the important role forests play in protecting the planet. 

Recently, devastating evidence has emerged that because of the damage done to the Amazon rainforest, it is losing its ability to store carbon. In fact various activities both natural and human-caused are leading to it in some cases releasing greenhouse gases such as methane and nitrous oxide into the atmosphere. As a result, scientists are extremely concerned by emerging evidence that parts of the Amazon are becoming a carbon source, not a carbon sink. 

Drying wetlands and soil compaction from logging, for example, can increase emissions of the greenhouse gas nitrous oxide, a study from March 2021 concludes.

Another study from May 2021 found that rising temperatures can slow down a tree’s ability to photosynthesise as quickly, although the process still happens. 

Why planting trees alone isn’t enough 

While all this evidence means it is vital that forests are protected and more trees are grown so that future generations can benefit from their carbon-capture capacity, there’s evidence that we can not rely simply on “planting trees” to save the world from climate change. 

In 2020 some scientific research suggested that if tree-planting initiatives are badly designed they can actually be unhelpful. That’s because of the risk of them creating not particularly diverse “monoculture” (meaning one type of species) areas of woodland, and because there is a debate about how much carbon very young trees can actually capture, according to an article about the studies by the BBC. 

Professor Eric Lambin from Stanford University pointed to a scheme in Chile that he found accelerated biodiversity loss. “If policies to incentivise tree plantations are poorly designed or poorly enforced, there is a high risk of not only wasting public money but also releasing more carbon and losing biodiversity," he said.

Activist Greta Thunberg has echoed this concern and told the Davos meeting where the 1 trillion trees initiative was launched that “paying someone else to plant trees” was not enough. 

​She has made it clear that tree planting efforts have to work alongside concerted efforts to stop our reliance on fossil fuels and cut emissions, and tweeted in 2019 that: “Yes, of course we need to plant as many trees as possible. Yes, of course we need to keep the existing trees standing and rewild and restore nature. But there’s absolutely no way around stopping our emissions of greenhouse gases and leaving fossil fuels in the ground.”

Thunberg has joined broadcaster Sir David Attenborough in supporting the idea of “rewilding” the world. In a film she created with writer George Monbiot they highlighted that means not just planting more trees, but protecting and restoring lots of different types of wild areas including mangrove forests, wetlands, and seagrass meadows that all play a role in carbon capture. 

It’s clear that planting trees is a useful tool that we can use to help mitigate the effects of climate change and protect the planet, but it’s something we need to research to do the right way alongside continuing our efforts to reach net-zero emissions.