Tree restoration potential, Q&A

When the journal Science published our paper on the global tree restoration potential in 2019, it grabbed headlines. We found that outside of urban and agricultural areas, there’s 0.9 billion hectares of land which could support new trees. Our estimates suggest this is room for approximately one trillion more trees than we currently have. (In 2015, we found the planet is home to three trillion trees.) With all the attention – which even led to the launch of the World Economic Forum’s Trillion Trees initiative ( – came questions about how trees can help mitigate climate change. We’ll answer some of them here.

Question: Are cuts to greenhouse gases no longer needed if the solution to climate change is simply to plant more trees?

Answer: No. To avoid catastrophic climate change, we need to quickly and drastically cut emissions, and we need to draw down the excess carbon that’s already in the atmosphere. Achieving this will require many solutions. Trees are not a silver bullet for climate change; what our research shows is that restoring trees is a powerful drawdown solution over time. Significant cuts to current emissions are still essential.

Question: Could planting trees help offset our annual carbon emissions?

Answer: Trees are not an offset for current or future emissions. Every year, the ocean absorbs about 30% of human-made carbon emissions, and terrestrial ecosystems absorb slightly less. The rest of our emissions enter the atmosphere. Over the years, this has caused the accumulation of ~300 Gt of excess carbon in the atmosphere. Our study finds an additional 0.9 billion hectares of forests could capture approximately 205 Gt carbon, i.e. two-thirds of the total human-made carbon emissions currently in the atmosphere.

Question: Is it really possible to plant a trillion trees?

Answer: No. To paraphrase a popular comparison between one million and one trillion dollars, if you started planting the day Jesus was born and planted a million trees every day, you still wouldn’t have planted a trillion trees today. (In fact, after more than 2000 years of daily planting at that massive scale, you’d still be under three quarters of the way to one trillion trees!) While tree planting can play a role in certain restoration projects, the tree potential paper is not a prescription for tree planting. Instead, it points to the tremendous capacity the Earth has for forested ecosystems and to the benefits we would see if we created the conditions where a trillion more trees could naturally flourish.

Question: Should trees be planted over natural grasslands or wetlands?

Answer: No. All ecosystems, including grasslands and wetlands, play vital roles for local and global environments. The aim of our study was to find the areas where trees would naturally exist, and our model highlights the areas where trees could be restored to their natural extent. It also highlights the huge regions around the world that should not support trees or that could support a very minimal level of tree cover, such as some grasslands.

Question: Don’t trees take too long to grow to affect climate change?

Answer: Tree restoration is not a quick fix for climate change. Restored trees will accumulate carbon slowly over the rest of this century and beyond. Like many climate change solutions, this is a long-term vision, which highlights the urgent need for action now. But restoration isn’t just about drawing down carbon. Practiced in ecologically and socially responsible ways, restoration has the power to restore the biodiversity and ecosystem services we all rely on for life. Nature wants to thrive, and it’s remarkable to see how quickly nature can return to restored areas.

Question: Are monoculture tree plantations effective carbon sinks?

Answer: No. As ecologists, we advocate for restoring natural levels of biodiversity. We support projects that restore a healthy diversity of native species in any location that should naturally support trees. That’s because biodiverse forests function as complex ecosystems – which can also capture significant amounts of carbon – whereas monocultures not only capture less carbon but also don’t support biodiversity and can even harm nearby ecosystems.

Question: How can I find out what tree species could grow where I live?

Answer: We’ve created a science-based open data platform for everyone, everywhere to connect to the global restoration movement our study helped inspire. Restor brings transparency, connectivity and ecological insights to restoration efforts around the world. To learn more about the tree restoration potential, read the full paper here, or explore a summary here.