Scientists have come closer to unravelling the true cause of the Mayan civilisation's demise

Between 750 and 900 AD, the Maya lowlands of Central America experienced a sharp demographic and political decline. The scientific literature has for decades attributed this event primarily to a series of severe droughts.

But analyses of sediments spanning the last 3,300 years partly cast doubt on this simple "climatic" version.

University of Montreal geography professor Benjamin Guinnett, an expert on environmental change and its impact on Maya civilisation, is studying the Itzan region of present-day Guatemala. Using sediment cores from Laguna Itzan Lake near an archaeological site, he and his colleagues are reconstructing the history of human activity and climatic conditions.

The results are published in the journal Biogeosciences.

The scientists studied three geochemical indicators in lake sediments:

• Polycyclic aromatic hydrocarbons (PAHs) - showing the intensity of fallow and slash-and-burn agriculture;
• "Waxy" leaf compounds - give an indication of vegetation type and precipitation levels;
• Faecal stanols - organic molecules whose concentration can be used to estimate population size.

So they simultaneously reconstructed the dynamics of population, land use and climate - from the first traces of human activity around 4,000 years ago to the final abandonment of Itzan around 1,000 years ago.

"Our data showed that the first permanent settlements appeared around 3,200 years ago," says Guinnett. - We see active fall fires and population growth. "During the Preclassic period (about 3,500 to 2,000 years ago), the Maya made extensive use of fire: burning the forest and then growing crops on the fertile ash.

A dramatic shift occurred in the Classic period, about 1,600-1,000 years ago: with markedly higher population densities, the intensity of fire use fell sharply.

"It is likely that much of the land had already been cleared, and this forced a shift to other farming strategies," the researcher explains.

Indicators point to an increase in intensive farming: ridge and furrow cultivation to reduce erosion, vegetable gardens, permanent plots. Fire ceases to be a key tool.

This transformation fits well with the archaeological evidence of the Maya heyday: a complex, urbanised civilisation with high specialisation and advanced agro-technologies adapted to the local environment.

But analyses of hydrogen isotopes in the "leaf wax" revealed the unexpected: unlike areas further north, where droughts are indeed recorded, in Itzan the climate has remained relatively stable.

"Itzan is located close to the Cordilleras, where moist air masses from the Caribbean Sea provide steady orographic precipitation," Guinnett explains. - "While other Maya regions suffered serious drought, here the rainfall pattern remained stable.

This is also important because a number of archaeologists believe that the "Maya collapse" began in the southwest, where Itzan is located. If there were no droughts here, they could not have been the initial cause of the decline in this region, notes the scientist.

At the same time, population markers show: in the final of the Classic period (about 1,140-1,000 years ago), the number of people in the Itzan area drops sharply, traces of agriculture disappear, and the place is abandoned.

How could a community that had water and favourable conditions perish, almost in sync with regions suffering from droughts?

"The answer is in the interconnectedness of Maya societies," says Guinnett. - Cities did not exist in isolation: they were united by a network of trade routes, political alliances and economic interdependence."

Drought in the central lowlands could set off a chain of crises:

• resource wars between cities,
• the collapse of royal dynasties,
• mass migrations,
• the breakdown of trade links,

all of which gradually hit regions where the local climate remained relatively favourable.

Thus, according to this logic, Itzan perished not because of a lack of water, but because it was drawn into the general collapse of the system of which it was a part. Inter-regional interdependence explains why it was not necessary to "scorch" an entire area with droughts to bring down civilisation: the effect spread far beyond the directly affected areas, like falling domino dice.

"The transformation or 'collapse' of Maya civilisation was not a simple mechanical consequence of a single climatic catastrophe," Guinnett concludes. - 'It was a complex process where climate, social organisation, economic networks and political dynamics were intertwined. Regional socio-political and economic factors played a crucial role.