Ancient Mayan Clearcutting Still Impacts Carbon in Soil Today

Even 1,000 years after a forest regrows, the soil beneath still won’t hold as much carbon as it once could, a new study suggests

Chichen Itza
Wikimedia Commons

There’s a popular notion that the ancient Maya lived in total harmony with the land, leading a sustainable lifestyle that took only what they needed from the vast tropical forests surrounding them. But that’s not really the case. The Maya deforested large swathes of land, cutting down trees in order to plant fields of corn, for firewood and for building their monumental temples. When a massive drought struck around 900 A.D., it's believed the society did not have the forests and other resources to fall back on, leading to the end of an empire. But it turns out in the intervening 1,100 years, the impact of that resource depletion can still be felt. Maddie Stone at Earther reports that a new study shows that clearcutting has impacted the soil’s ability to store carbon, a finding that has big implications for modern societies.

Today, much of the land cleared by the Maya has been reclaimed by the rainforest, and one would think the area has completely recovered from the exploitation. But in a new study in the journal Nature Geosciences, geochemist Peter Douglas of McGill University and his colleagues examined soils from the area. According to a press release, they extracted sediment cores from three lakes in the Maya lowlands of Mexico and Guatemala. They then used radio-carbon dating to get the ages of plant waxes, molecules produced by vegetation that bind with minerals and last a very long time. The waxes wash out of the soil into the lakes. When the age of the plant waxes is compared to the age of fossils in the sediment cores, it can tell researchers how long those plant waxes, and presumably soil carbon, has been in the ground. The larger the age gap between the waxes and the fossils, the longer the carbon has been sequestered in the ground.

What the study shows is that once the Maya began deforestation, the soil began to lose its ability to store carbon long term. Over the past 3,500 years, which includes the time the Maya were active in the region, the age of the plant waxes decreased from 70 to 90 percent, a sign that the soil is simply not holding as much carbon as in pre-Maya times, instead releasing it into the atmosphere.

“When you go to this area today, much of it looks like dense, old-growth rainforest,” Douglas says in the release. “But when you look at soil carbon storage, it seems the ecosystem was fundamentally changed and never returned to its original state.”

The finding has implications for climate change predictions since it alters how much carbon second growth forests are believed to sequester. “This offers another reason -- adding to a long list -- to protect the remaining areas of old-growth tropical forests in the world,” Douglas says. “It could also have implications for how we design things like carbon offsets, which often involve reforestation but don't fully account for the long-term storage of carbon.”

Susan Crow, a soil ecologist at the University of Hawaiʻi at Mānoa, not involved in the study, tells Stone at Earther that the study shows new analysis techniques have the potential to help us understand the complex way carbon cycles between soil and the atmosphere. “We are counting on reforestation as a critical climate change mitigation action in [the] near future,” she says. “[T]his paper seems to question the effectiveness of this strategy.”

In the release, Douglas cautions that these findings may not apply to other tropical forests around the world that have also been impacted by agriculture or clearcutting, but he’d like to use the technique to analyze those soils as well investigating how permafrost’s ability to store carbon has changed during previous periods of climate change.

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