Blog type: Scientific research

Originally published: A previous version (slightly different to here) was published in a Mongabay article and presented in a Zeromission webinar on best-practice methods to planting trees in the correct geographic location.

Background: Ed Mitchard is a Professor at the University of Edinburgh, who studies changes in land cover, forests and forest carbon stocks globally using a combination of field studies and satellite remote sensing data. He also previously served as the chair of the Plan Vivo TAC and currently remains a TAC member.


The current climate crisis calls for efforts on two fronts: first off, we must reduce CO2 emissions to the atmosphere, and secondly we must support the communities that are most at risk from climate change. Thanks I think to activists like Greta Thunberg and pervasive news coverage of large-scale fires in Australia, the Americans and Siberia, there is greater awareness and engagement globally on the urgency of tackling our warming climate. Also gaining more attention is the vastly unjust impacts of climate change – that the least well-off groups are feeling climate change the most. Rural populations in the Global South, from farmers in Nicaragua, to Tanzanian hunter-gatherers, to forest dwelling groups in Indonesia, are all experiencing the impact of climate change through less predictable weather patterns and increased natural disasters. Thankfully, one initiative can address these twin crises: tree planting in tropical regions.

There are many necessary paths to reducing CO2 emissions. We know we need to cut emissions from across our power, transport and industry sectors. And we must stop tropical deforestation. Forest clearing has represented about 15% of our emissions to the atmosphere since the Rio Declaration in 1992. This tragic loss has also has prevented this forest from sucking up a proportion of the carbon we release from burning fossil fuels, something the dwindling intact forests continue to do. To this end, REDD+ initiatives in the tropics, which reduce emissions from deforestation and forest degradation, are increasingly important. Community driven REDD+ projects, such as Bujang Raba and the Yaeda Valley project, can deliver significant positive impacts on the climate, while also improving the lives of marginalised communities.

However, it is clear that reducing emissions drastically and stopping deforestation, while necessary, are not by themselves sufficient to keep global warming below 2 degrees (a level that itself may not be safe for hundreds of millions of the world’s people). We must also suck out massive amounts of carbon from the atmosphere, partly because emissions reductions cannot run fast enough, and partly because we’ve already emitted far too much carbon.

In order to protect our lifestyles in the West, and even the livelihoods and homes of many of the world’s poorest people, we need to go further and keep warming to just 1.5 degrees. For example, this will protect many (though not all) island states and coastal settlements from becoming unhabitable due to sea level rises. In order to do this, the International Panel on Climate Change states that much more CO2 will need to be actively removed from the atmosphere in the 2020s and 2030s, before we get to net zero. In order to suck this CO2 from the atmosphere, tree planting and forest restoration are essential, and we need to scale up our current paltry efforts urgently.


The social benefits of tree planting

There are clear social and biodiversity reasons to plant trees in the tropics. Not only do the trees remove carbon from the atmosphere, but trees improve the local environment. Trees lower the local temperature, provide shade, stabilise the ground to protect against landslides and the damage caused by heavy rain, and often provide non-timber products such as fruits which can improve nutrition or diversify local incomes.

Tree planting projects can channel income to rural communities through payments for ecosystems services (PES), which greatly improve the livelihoods of rural communities. Plan Vivo’s certified projects all provide benefits for communities and biodiversity, as 60% of the money from the sale of carbon credits – called Plan Vivo Certificates – flows directly to the project participants, themselves some of the poorest people on the planet. Thus carbon funds are used not just to lock up carbon, but directly to tackle issues like poverty, food insecurity and gender inequality.

These projects create much more than forests. The trees planted through the Halo Verde project in Timor Leste fund a scholarship for more than 450 girls to finish high school, and improves crop quality to ensure locals have enough to eat. In Ethopia, EthioTrees works with landless farmers to tap and produce frankincense oil, contributing to the livelihoods of some of the most vulnerable people in the region. And further, these financial and environmental benefits provide direct resilience for these communities against some of the impacts of climate change, such as the increased incidence and severity of extreme weather events.


Trees grow quickly in the tropics

There are also scientific reasons to plant trees in the tropics rather than in more northern regions. Fundamentally, trees grow much faster in the tropics, and land and labour is much cheaper there. Therefore, for a given financial investment, more trees can be planted in the tropics over a larger area, and these trees will capture carbon faster than an equivalent number outside the tropics. These differences are significant: I have seen newly restored forests in tropical Peru reach 15 m height in about 6 years, whereas a Scots Pine planted in the Scottish Highlands might take 60 years to achieve that height. This will translate directly into carbon storage, suggesting per hectare carbon sequestration rates in Scotland might be just a tenth of that in the tropics.

Tree growth in the Scottish highlands (left) is at a slower rate than in the tropics, illustrated by a photo of smallholder woodlots from the Trees for Global Benefits project (right)


This not only means that costs for achieving the same carbon capture in far northern latitudes are far higher, but also that the land footprint is far greater. It does not mean we should not be restoring forests in the Scottish Highlands: that has positive ecological and social value too, and will capture significant quantities of carbon in the longer term. But it does not seem to me to be an efficient use of financial resources for carbon sequestration –  tropical forest restoration or agroforestry projects are more sensible from a financial and land footprint standpoint per unit of carbon.  

There is another complicating factor: the albedo effect. This describes how reflective the Earth’s surface is, and is one of the nasty feedback loops of climate change: as the climate warms, there is less ice cover in the oceans, and less snow cover on land, meaning less heat from the sun is reflected back into space, and the Earth warms faster. This is probably the main reason the arctic is warming so much faster than the rest of the planet. Planting trees in the tropics has little further impact on the albedo effect – non-forest and forested surfaces in the tropics have pretty similar albedo. But in much of Nordic areas like Sweden and some the more mountainous regions of Scotland, the impact is highly significant: trees are much darker than the snow that would otherwise lie on the land for much of the year. Thus planting trees in northern places, while it will still (slowly) take carbon out of the atmosphere, might actually warm the planet more than leaving things as they are.

 Diagram depicting how the albedo effect differs in forested and snowy regions


MAX Burgers investing in co-benefits

So, where is money to plant trees in the tropics to come from? One answer is government funding for ecosystem restoration (e.g. see Bonn Challenge commitments). But companies taken together have more financial firepower, and many are looking to offset their carbon emissions to meet various Net Zero targets. A leader in taking its climate responsibilities seriously is MAX Burgers, a large Scandinavian fast food chain. MAX was ahead of the curve in the mid-2000s when it started working to reduce emissions from its supply chain and operations as much as possible, and then offset residual emissions through purchasing carbon credits that funded tree planting projects in the developing world through the Plan Vivo carbon standard.

It continues to offset its residual emissions now, in fact making its food ‘climate positive’, offsetting more emissions through tree planting for every meal sold, than is released through their entire value chain. Large Scottish brewery Brewdog recently made a similar pledge, that its beer will be ‘carbon negative’, due to reductions in supply chain and production emissions, and tree planting. MAX have funded farmers to plant trees on their farms in countries in the Global South – whereas Brewdog, like many others, have chosen to plant their trees closer to home (in the Highlands of Scotland in this case). While these projects will capture carbon in the longer term, tree planting in Scotland does not deliver the same kind of social benefits as tropical tree planting does. Companies should direct their investments towards carbon capture that improved the incomes and local environment of developing countries (possibly in addition to restoring ecosystems closer to home, e.g. under rewilding, climate resilience or biodiversity badges, rather than for carbon offsetting).

All of us must address climate change urgently. We must ensure politicians set ambitious climate goals, and companies should remove emissions from their supply chain as much as possible, and remove all incentives and legal pathways for new deforestation. Any residual emissions should be offset, and in order to support communities at the forefront of the climate crisis, I believe these offsets should come mostly through a massive expansion in agroforestry and forest restoration projects across the tropical regions. In order to capture carbon in the most efficient manner, and provide a host of environmental and social benefits, tree-planting in the tropics is an essential investment.