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Breaking Down Carbon Markets: Planting Trees May Not be So Green After All

Updated: Mar 7

"Until you dig a hole, you plant a tree, you water it and you make it survive, you haven’t done a thing. You are just talking."  Wangari Maathai

Protecting and expanding/starting forests are the most well-known/oft-used carbon offsetting projects. This is because storing carbon in plants is seen as the most effective means of pulling carbon dioxide out of the atmosphere.

But while the Bonn challenge planted the dream of expansive old forests in many minds across the globe, it wasn’t clear where 350 million hectares of forests would be able to sit for decades to help reduce global carbon emissions.

That is until “The global restoration of tree potential” was published in Science in 2019. Jean-Francois Bastin and colleagues generated a model that proposed the planet could support an additional 900 million hectares of forest — more than 2-and-a-half times more forest area than the Bonn challenge’s goal.

Conservations and ecologists, however, strongly disagreed with Bastin’s findings [comments 1, 2, and 3]. They believed the forest model omitted fundamental ecological assumptions about where trees could be planted and that the model misallocated forest area to regions where trees could, in fact, not be planted.

But it was too late.

Galvanized by crystal clear findings, millions around the world gathered to plant trees, from the White House to the edge of the Sahara Desert.

Climate anxiety is fast on the rise around the globe, and many people are, rightly so, looking for solutions – any solution.

Trees are often seen as symbols of natural stability – bracing themselves amid seasons, storms, and shifts in our planet’s climate – and shelter, cooling the air around them and sucking up stormwater runoff.

Still, trees are not perfectly resilient; in some regions, including Canada, where wildfires burned all summer, forests may have reached a tipping point.

Those forests, however, may not have been forests at all and instead were "tree farms" or monocultures of trees. A large proportion of the forests planted – some 45% – for the Bonn Challenge were instead monocultures, tree plantations.

Many of these projects fail. Trees and forests by extension, are resilient because of the relationships they build in their diverse communities. As Claire Cameron wrote for The New York Times, however, extensive monocultural "tree farms" posing as forests are planted with trees evolved to burn without natural buffers to prevent fires from spreading otherwise.

Still, according to the U.N.’s definition of forest, which was only recently re-evaluated, a tree plantation would have been a forest: the U.N.’s former definition of forest was “any area of land spanning more than 0.05 hectares with tree crown cover (or equivalent stocking level) of more than 10% with trees with the potential to reach a minimum height of 2-5 meters at maturity in situ.” (That definition has since been changed to “land spanning more than 0.5 hectares with trees higher than. 5 meters and a canopy cover of more than 10 percent, or trees can reach these thresholds in situ. It. does not include land that is predominantly under agricultural or urban land use.”) further found that nearly two-thirds of the Bonn Challenge projects were agricultural projects under the guise of reforestation projects (45 percent of projects are monoculture plantations; another 21 percent are agroforestry projects that mix trees and crops – which are essential carbon offsetting projects if the goal is reimagining our global food systems; however, these projects should not be conflated with fundamental ecological processes associated with forests).

Some tree plantations were even planted at the expense of deforesting standing forests. Take the Sowing Life project in Mexico in 2018, for example, an old-growth forest the size of New York City was cleared away for young, fast-growing, carbon-guzzling trees.

And monocultures of trees aren’t just less resilient, but they are also worse at pulling down carbon dioxide than biodiverse forests.

Moreover, a recent study published in Nature finds timber harvests are actually contributing to carbon emissions contrary to the carbon neutrality promises tree-planting projects provide us.

Wood products derived from trees harvested at tree plantations are considered ‘carbon neutral’. This is because additionality, the foundational component of all carbon credits, is always about a baseline subject to the interpretations of the project developers. This means that carbon lost by trees harvested may be overestimated if the project developers believe that more carbon would have been lost due to someone else harvesting in an alternative scenario or “counterfactual.”

As a result, many carbon offsetting projects, and subsequently countries, report the effect of planting trees that will be harvested for timber as a net carbon benefit. However, accounting for the emissions without this counterfactual, the research team found that tree harvesting contributes up to 10 percent of annual carbon emissions.

However, the study concludes on a positive note: these emissions were not new but rather existing ones that were appropriately identified. These emissions can be adequately reduced now that they have been identified.

But, again, not all projects are agricultural projects disguised as afforestation projects. For example, some tree planting projects fail because of mismanagement or catastrophe – fire, disease, or drought. So those failed projects, including those in India and Turkey where millions of trees were lost, also inadvertently contribute to carbon emissions.

Most standards require that projects set up a buffer pool in case of these unforeseen circumstances, but those buffer pools can be unreliable. Sometimes buffer pools are filled with low-quality carbon credits that can result in leakage – carbon lost elsewhere as a result of the project – say, someone harvests trees from somewhere outside the project area – or are made up of risky projects that are not resilient to catastrophic events. Thus, buffer pools may also overestimate carbon credits.

Ultimately, the best way to ensure we can rely on trees to pull down carbon dioxide and cycle it efficiently is to let them do what they do.

But telling people to plant fewer trees and let forests grow independently might be a hard sell. In 2022, One Tree Planted and its global partners planted 52 million trees. And that number is growing exponentially: in 2015, OTP and their partners planted 50,000 trees; in 2018 1.3 million trees were planted.

Leading organizations are putting down trees fast and making a lot of money doing it.

On a warming planet – the hottest it has ever been in tens of thousands of years – global interest in tree planting projects and the carbon credits that fund these projects is increasing fast, and the Voluntary Carbon Market is struggling to keep up.

In the next article, I will talk about the growing distrust in the Voluntary Carbon Market and the expressed need for consolidation of standards validating projects to ensure that VCMs can continue to grow into an effective industry for reducing greenhouse gas emissions and mitigating climate change. 



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