The Amazon rainforest is being  cut down at a terrifying rate.

One estimate suggests it’s  losing 18 trees per second. And putting that forest back isn’t  as easy as tapping the undo button.

It’s a complex process that takes years. But one group of researchers thinks  that they’ve found a shortcut… by copying the notes of people  who lived 2500 years ago. [♪ INTRO] As the world’s biggest rainforest, the Amazon has a huge role in  our planet’s carbon balance. Naturally, that means some folks  want to bring back what’s being lost.

Some researchers want to start  from the ground up – with the soil. The idea is that if you can identify  beneficial microbes to enrich the soil, and maybe throw in a few nutrients, you’ve got a solid foundation on which  to build, well, a whole rainforest. And it sounds kinda high-tech, right?

Well, what if somebody already  did all the work 2500 years ago? The key to reversing rapid  deforestation while staring down the barrel of the climate crisis may lie with something called Amazonian  Dark Earth, or ADE for short. This stuff is exceptionally fertile  soil found at sites inhabited by pre-contact indigenous peoples  as long ago as 450 years BCE.

For context, at that time The Art of War  was just being written in ancient China, and that Alexander guy wouldn’t get around to conquering his known world  for almost another century. ADE is rich in nutrients such  as carbon, calcium, phosphorus, zinc, iron, and copper, all of which  are great for growing healthy plants. Researchers can’t quite agree  whether ADE was created on purpose for growing plants by the indigenous  societies of the Amazon basin, or whether it’s just a  by-product of people living there and just generally doing people stuff.

And that’s because many of the elements  that make ADE such great plant food are naturally occurring in the Amazon  river floodplains where these folks lived. But ADE also includes micronutrients  that may have resulted from many generations of people stuff,  such as charcoal from the fires they used to cook their food or burn trash,  leftover items from their meals such as animal bones and bits of fruit and  vegetables, and even pieces of pottery. So even if it is accidental,  it’s still such good stuff that we can see the difference  as much as 2500 years later.

In a 2023 paper, a group of scientists  from Brazil published a demonstration of how ADE could help turn land cleared for  cattle pasture back into a restored forest. Their simulation was designed to  mimic the succession of plants. Plant succession describes what happens when the species in an area gradually replace,  or succeed, one another over time.

Primary succession occurs when organisms  colonize an area for the first time. Hardy, so-called pioneer species move in first. Stuff like lichens and small plants  that don’t require much soil to grow.

After that comes grasses. As those species live and die, they’ll  gradually create a nutritious soil that can support the growth of larger  secondary species, such as shrubs. As this process continues, eventually the habitat can support growing swaths of large trees.

And over hundreds of years, these  forests become climax communities, which is when the plant and animal  species in an area have basically reached a point where they’re in balance with  one another, and succession ends. But the situation in the Amazon  is a little bit different, because life isn’t moving in for the first time. Secondary succession happens when a  climax community, such as the Amazon rainforest, experiences a disturbance  like a fire or intentional deforestation.

The stages of secondary succession are  similar to those of primary succession, typically beginning with grasses and small plants, which are replaced by shrubs and  small trees after a few years. And eventually, the forest can  return to the climax community that was present before the disturbance. This is what the researchers in that  2023 paper wanted to simulate to determine how well ADE can support plant growth; they wanted to see if it could  help the plants come back.

So, the researchers first grew  samples of the most common Brazilian pasture grass to  simulate a cattle pasture. They grew the grass in three different  conditions: soil with 20% ADE, soil with 100% ADE, and regular old  agricultural soil that served as the control. After letting the grass grow for several weeks, the researchers cut the  grass, leaving only the roots.

To mimic ecological succession from  a pasture to a restored forest, the researchers then grew  Amazonian plants from the three stages of succession in those same pots. They also kept the temperature of their  greenhouse at about 34 degrees Celsius, to imitate the very toasty  climate crisis-driven future. And the researchers found that the  soil with 20% ADE showed similar growth to the 100% sample for the  secondary and climax plant species.

After planting, the ADE-enriched samples  also maintained a greater diversity of microbes than the control soil,  meaning that in addition to supplying essential plant nutrients, ADE  also supports beneficial microbes that help with nutrient uptake. So a tasty treat for plants all around. That shows that soil with just 20% of  the nutrients and microbial richness of undiluted ADE would be good enough to support the plants present during  later stages of ecological succession.

So tasty… and strong. The researchers say they wouldn’t  just dig up and use all of the ADE because it would, you know, eventually run out. Instead, it would make more sense to use ADE-enriched terrain as a  model to create better soils.

By mimicking ADE’s nutrient  profile and microbe composition, scientists think they can create a super soil that can improve forest restoration efforts. So whether ADE was a lucky accident,  or an intentional way to improve soil, it’s clear that the land use practices  of the indigenous peoples of the Amazon were so sustainable that the terrain they lived on can inspire methods for  reforestation 2500 years later. And they created such a durable  legacy that these ancient peoples might just be giving us clues  about how to save their home today.

Thank you for watching this SciShow video, which was supported by our patrons on Patreon. Just like Amazonian Dark Earth, you  help this channel grow and thrive, and without you we’d be worse off – so thank you. And if you’d like to join our  amazing community of supporters, you can get started at patreon.com/scishow. [♪ OUTRO]