• Planting new forests is recognised as a powerful natural climate solution, but the best way to achieve this is still a matter for debate.
  • New research suggests natural regrowth could be the most effective approach.
  • Letting nature take its course promotes native species and biodiversity at a fraction of the cost of manual tree-planting.

Susan Cook-Patton was planting a native red oak seedling in her backyard. As she finished and stepped back to admire a job well done, she noticed a much larger red oak seedling growing nearby. This other tree had sprung up from a forgotten acorn planted by a squirrel and was growing healthily all on its own. While many of us like to plant trees, moments like these should remind us that nature has been growing trees and forests without our help for millions of years. In fact, under the right conditions, nature can do this much better and more economically than humans can ever hope to do.

Trees are having a moment in the limelight as people increasingly recognize their ability to soak up CO2 from the atmosphere and store it for long periods of time. While new forests represent a powerful natural climate solution, there is a lot of confusion and controversy about how to best establish those new forests.

We want to dispel the myth that people always need to actively plant trees. If new forests are going to be part of the many solutions needed to address climate change, planting tree by tree will take more time and money than we have. Of course, there will always be places that need planting – if the site is too degraded, if there are not enough seeds nearby, or if we want to encourage particular tree species – but we should always ask first if nature can grow the trees without us or with just a little bit of help.

Natural forest regrowth involves simply stepping back and letting the forest recover, but could also involve removing factors that prevent regrowth, such as grazing cows, aggressive weeds or unnatural fires. And with this natural regrowth comes enormous benefits.

With 31 collaborators worldwide, we recently published a new map in the journal Nature that shows the potential carbon capture from letting forests grow across different areas of the globe. We found that these regrowing forests can capture substantial amounts of carbon, more than we previously thought and especially in the tropics. The map is available at Global Forest Watch and is free for anyone to use.

On top of capturing CO2, natural forest regrowth can cost substantially less than active tree planting. For example, a study published this year found that implementing assisted natural regrowth in the Atlantic Forest region of Brazil costs 77% less than full tree planting and could save $90.6 billion.

The map predicts accumulation rates if natural forests younger than 30 years are growing there and shows savanna biomes with hatched lines to flag that restoration of forest cover should proceed with particular caution in these grassland-tree ecosystems.
The map predicts accumulation rates if natural forests younger than 30 years are growing there and shows savanna biomes with hatched lines to flag that restoration of forest cover should proceed with particular caution in these grassland-tree ecosystems.
Image: Nature

Natural forest regrowth may also better promote the re-establishment of local tree species that are best equipped to survive in a given location and support the many organisms that eat them or dwell amongst their branches and roots. Remnant trees, hedgerows and living fences in pastures can especially hasten biodiversity recovery and enhance colonization of species more typical of mature forests. In general, biodiversity recovery increases with the amount of surrounding forest cover and biodiversity-friendly cropland, and decreases with the amount of urban development.

While natural forest regrowth represents a great tool for capturing carbon and creating habitat for biodiversity at a fraction of the cost, to reap the benefits we have to keep the forests standing and growing. Young regrowing forests can be especially vulnerable to being cut down again, because people view them as less valuable or as a temporary land cover. Developing financial tools to incentivize keeping forests in place and/or planting some commercially valuable trees in naturally regenerating forests represent potential options for encouraging the maintenance of young forests. It is important to monitor both naturally regrowing and planted forest to ensure that forest cover is actually increasing, and, if not, take corrective actions to improve outcomes. Fortunately, new technologies, such as smartphones, drones and high-resolution satellite imagery make widespread tree cover monitoring more practical.

Our recently published map will tell you how much carbon can be stored when the conditions are right for natural forest regrowth. But regrowth can be highly variable from one spot to the next. For those places that need a little extra help to speed up the rate of forest regrowth, there are lots of ways to adopt a 'planting-lite' approach. For example, we might clear competitive pasture grasses around naturally established tree seedlings, or plant small clusters of tree seedlings to jump-start forest recovery.

When thinking about new forests as a climate-mitigation strategy, it is important to remember that regrowing trees is only one piece of the puzzle. A stable future climate requires revolutions in our energy sector and massive efforts to reduce greenhouse gas emissions. It also requires keeping existing forests as forests. The World Economic Forum’s 1t.org initiative specifically focuses on conserving forests, restoring existing forests and growing new forests in that order for a reason. Protecting existing forests and improving their management is cheaper and more effective for mitigating climate change than regrowing forests after the fact. However, in those places where we have already lost our forests and where the conditions are right, we can harness the power of nature to help create a future in which both people and nature can thrive.