Is Tree Restoration the Most Effective Climate Drawdown Strategy?

Signs of soil erosion near Sandhikharka, Nepal. (©Chris Steele-Perkins/Magnum Photos for FAO)

In recent years, many countries have expressed a willingness and demonstrated the capability to increase forest cover and restore degraded landscapes. As of 2018, pledges had reached upwards of 168 million hectares. The latest confirmation of this growing momentum can be seen in the recent UN General Assembly’s declaration of the UN Decade on Ecosystem Restoration 2021–2030 which will help countries fight against the impact of climate change and biodiversity loss. The Food and Agriculture Organization of the United Nations (FAO) and the UN Environment Programme will lead the implementation; of the decade with countries and partners. However, the question remains about whether we are being ambitious or strategic enough with our restoration commitments.

New research, published in the journal Science, led by scientists at ETH Zurich’s Crowther Lab, addressed this question head-on, using innovative machine learning approaches to refine estimates of the climate change mitigation potential of tree restoration and quantifying the earth’s tree carrying capacity through The Global Tree Restoration Map. The work, a collaborative effort with FAO utilized FAO’s Open Foris suite of free open-source solutions for environmental monitoring. The article received an immense media following and a wide array of feedback. We spoke to lead author Jean-François Bastin and principal lab investigator, Tom Crowther, about the latest findings.


What was the big question you were trying to ask and what were your most important findings?

We set out to quantify the global potential for tree cover and forest restoration and estimate what forests could offer as a nature based solution to climate change (in terms of carbon drawdown).

In order to inspire behavioural change, we felt we needed to know the size of this solution, so that individuals and communities can understand how their efforts could contribute to combating the climate crisis, which can be a daunting and paralyzing issue. Ultimately, our results were surprising, even to us.

Our research showed that out of the drawdown solutions currently available, tree restoration and storage potential on land could remove up to 2/3rds of the 300 Gt of accumulated carbon in the atmosphere emitted by human activities since the beginning of the industrial era. All this through the addition of 0.9 billion hectares of canopy cover. This correlates to the IPCC report which suggests that increasing the world’s forest cover by 1 billion hectares will be necessary to help limit global warming to 1.5 degrees Celsius. This is an unbelievably powerful tool.

Although it should not replace efforts to reduce deforestation and forest degradation, which prevent new carbon emissions and conserve biodiversity, it has an enormous potential to enhance absorption of carbon already existing in the atmosphere. Carbon capture through restoration is often viewed as a “nice to have,” but this study stresses the vital importance of increasing attention to restoration efforts as a key solution to mitigate climate change impacts.

Another key message of your work is the urgency for action. Can you tell us why immediate restoration planning and interventions are so important?

There is an obvious need for immediate action to avoid the most severe impacts of climate change and temperature increases above 1.5 degrees. This will undoubtedly require a portfolio of climate solutions, but when it comes to restoration, a longer-term outlook is required. Ecosystems can take decades to achieve their full carbon storage potential so the sooner we act, the better. Our view is that this is a very effective carbon drawdown mechanism. It is equally, if not more important, that we drastically cut the annual emissions (of about 10 Gt of carbon) that humans continue to emit into the atmosphere.

In addition, our work showed that as the climate changes and becomes warmer and drier, we are likely to lose about 15% of the identified areas suitable for tree growth. This is a significant decrease and represents lost opportunities for both climate mitigation and biodiversity enhancement through habitat creation, hence the necessity for immediate action. We are not saying the results will be felt right away, and we recognize that restored trees will accumulate carbon slowly over the rest of this century. But like all climate change solutions, this is a long-term vision that highlights the urgent need for action.

Are we being ambitious enough with our restoration targets?

Comparing restoration commitments from the Bonn challenge with our tree restoration potential map revealed that around 10% of countries had overcommitted to restoration goals. Overwhelmingly however, our map showed that many of the Bonn challenge pledges could be substantially more ambitious. Many countries (43%) pledged less than half the area suitable for tree growth in that country and their commitments and goals could be increased accordingly. While recognizing that restoration is a challenging endeavour, with socio-economic considerations and multiple stakeholders and interests, if implemented correctly, it is amongst our most powerful tools to draw carbon down from the atmosphere, and it should be prioritized for its multiple other benefits (e.g. food and medicine production, as well as air and water filtration). We hope our work will serve to not only inspire increased action and engagement, but also to help countries re-evaluate their commitments.


Putting science into action - providing tools for restoration monitoring

The FAO-ETH collaboration will capitalize on this innovative science by bringing new tools to countries through Open Foris SEPAL. This will not only give countries the opportunity to use The Global Tree Restoration Map, but it will also allow them to apply the methodologies in building their own analyses for local restoration opportunities. Through a project funded by the Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF), the collaboration will work with four countries in Africa (Uganda, Kenya) and Asia (Myanmar, Cambodia) to offer new and effective ways of monitoring restoration. The project will complete its global component at the end of 2019 and will be moving to its in regional phase by supporting countries in capacity building activities to enable national institutions to more effectively monitor and report on their restoration efforts.

Casamance river in Senegal as seen by Landsat 8 satellite imagery in SEPAL (©FAO SEPAL)

Tools in SEPAL are already being used by over 3,000 experts in 159 countries to rapidly assess forest change due to deforestation and degradation using cloud-based supercomputers. In 2019, a specific restoration-monitoring module will be developed for identifying the biophysical potential for restoration and measuring forest enhancement due to restoration. Most importantly, SEPAL users will be able to recognize when interventions are bringing the expected results.

Further, a FAO Forestry working paper is scheduled for release in the latter half of 2019. The working paper will focus on the assessment and monitoring of both biophysical and socio-economic indicators and will address the need to align and improve guidelines on restoration interventions, paramount to the success of the UN Decade and ensuring progress towards both regional and global restoration commitments.

Useful links:

The global tree restoration potential” by Jean-Francois Bastin & al. in Science

The Global Tree Restoration Potential Overview Video

Tree restoration potential, Q&A

UN Decade on Ecosystem Restoration website

Voluntary Guidelines of National Forest monitoring

Open Foris and SEPAL

Global Landscape Forum (Bonn, 2019) plenary on Decade on Ecosystem Restoration

GLF Digital Summit session “Restoring Ecosystems, Reviving hope”


Khalil Walji works as capacity development specialist within the Forestry Department and is working on the FAO project, “Mitigation potential of global actions to enhance forest carbon stocks,” funded by the Ministry of Agriculture, Forestry and Fisheries of Japan.

Yoshihiko Aga is a Forestry Officer leading the FAO project on “Mitigation potential of global actions to enhance forest carbon stocks,” funded by the Ministry of Agriculture, Forestry and Fisheries of Japan.

Yelena Finegold is a Forestry Officer at FAO focusing on remote sensing and satellite land monitoring and is a co-author of The global tree restoration potential study.

About those interviewed:

Dr Thomas Ward Crowther is a Professor of Global Ecosystem Ecology at ETH Zurich where he formed the Crowther Lab.

Dr Jean-François Bastin is a Postdoctoral Researcher at ETH Zurich Crowther Lab.

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