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.
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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.
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