More fuel for early Anthropocene

New research from the nation of Belize, Central America, has revealed that ancient Maya culture responded to population and environmental pressures by creating massive agricultural features in wetlands, potentially increasing atmospheric CO2 and methane through burning forests and farming.

Earlier studies had suggested that the Maya’s advanced urban and rural infrastructure had alter ed ecosystems within globally important tropical forests.

But the new work – the first to combine airborne lidar (light detection and ranging) imagery with excavation and dating evidence in wetlands – found the Birds of Paradise wetland field complex to be five times larger than previously discovered, and found another, even larger, wetland field complex.

The Maya peoples developed their civilisation over millennia, beginning about 4000 before present (BP). Their lands covered parts or all of modern-day Mexico, Guatemala, Belize, Honduras and El Salvador.

The Maya cultivated crops and had developed cities with monumental architecture by about 2500 BP; the culture is noted for its calendar, astronomy, mathematics, art and complex system of writing.

The civilisation largely collapsed in the 9th century but endured in reduced form until the arrival of the Spanish, who invaded Mayan lands in stages between 1521 and 1697.

The new study, published in the Proceedings of the National Academy of Sciences, shows the Maya had “earlier, more intensive and more wide-ranging anthropogenic impacts” on globally important tropical forests.

This adds to the evidence for an early and more extensive Anthropocene – the period when human activity began to greatly affect Earth’s environment.

“We now are beginning to understand the full human imprint of the Anthropocene in tropical forests,” says study lead author Tim Beach, from the University of Texas at Austin, USA.

“These large and complex wetland networks may have changed climate long before industrialisation, and these may be the answer to the long-standing question of how a great rainforest civilisation fed itself.”

The study team examined 250 square kilometres of high precision laser imagery to map the ground beneath swamp-forest canopy, revealing the expansive ancient wetland field and canal systems that the Maya depended on for farming and trade through periods of population shifts, rising sea levels and drought.

Evidence showed that the ancient civilisation faced environmental pressures including rising sea levels in 3000–1000 BP and droughts in 1200–900 BP. They responded to these challenges by converting forests to wetland field complexes and digging canals to manage water quality and quantity.

The study team further posits that the Maya responded to large population shifts and changing demands for food production about 1800–1000 BP by expanding their network of fields and canals. Evidence of multiple ancient food species, such as maize, and animal shells and bones – indicating widespread protein harvesting – were uncovered in the study area.

The researchers believe the Maya’s wetland footprint could be even larger; modern ploughing, draining and sediment accumulation may be obscuring evidence.

Additional research on the region and its surrounding areas is already revealing the extent of wetland networks and how the Maya used them, painting a bigger picture of the Maya’s possible global role in the Early Anthropocene.

The researchers suggest that forest burning and the creation of wetland farming added atmospheric CO2 and methane. The largest pre-modern increase of methane, from 2000 to 1000 BP, coincides with the rise of Maya wetland networks, and those in South America and China.

“Even these small changes may have warmed the planet, which provides a sobering perspective for the order of magnitude of greater changes over the last century that are accelerating into the future,” Beach says.

“Our findings add to the evidence for early and extensive human impacts on the global tropics, and we hypothesize the increase of atmospheric carbon dioxide and methane from burning, preparing and maintaining these field systems contributed to the Early Anthropocene.”