Resilience of crops confirms that drought alone did not cause a ‘collapse’ in Mayan civilisation

The cause of the Mayan civilisation’s collapse is a puzzle. Something changed in the ninth century CE, and major sites like Palenque, Copán, and Tikal were abandoned. This coincided with a period of droughts during which average rainfall halved, reducing water reserves. The droughts came shortly after a shift in the diet of the elites towards maize – a plant that would have suffered in a drought and a popular theory is that the droughts made maize unviable, leading to famine. But had the Mayans become reliant on maize? Scott Fedick and Louis Santiago have investigated the Mayan diet and found the Maya had nearly 500 edible plants available to them, many of which are highly drought resistant.

Rather than concentrate on the most visible crops, Fedick recently compiled a master list of indigenous Maya food plants that draws on decades of Maya plant knowledge. Faced with much speculation about drought as the cause of Maya social disruptions, he and Santiago decided to examine all 497 plants on the list for drought tolerance.

“When botanists study drought resistance, they’re usually talking about a specific plant, or a particular ecosystem,” Fedick said in a press release. “One of the reasons this project was so challenging is because we examined the dietary flora of an entire civilization — annuals, perennials, herbs, trees, domesticates, and wild species. It was a unique endeavor.”

While examining the plants, Fedick and Santiago also considered what kind of rainfall change mattered. In their paper, they write: “Reduction in annual rainfall due to drought can manifest in various ways, and plants have a high diversity of responses to drought. A short-term drought could have a catastrophic impact on rain-fed herbaceous crops without any effect on woody tree crops with roots that reach the water table. Lengthening the dry season could have significant impact on agriculture and plant growth, while decreasing rainfall during a rainy season of normal length could have little or no impact on agriculture or plant growth, as long as the ground retained enough moisture for the plants to grow. It should be noted that an excess of wet season rainfall, usually a result of hurricanes or tropical storms, can also severely impact crops and livelihoods of Maya farmers. Much of this interseasonal rainfall variation can be masked by annual precipitation records.”

The authors found that while corn, beans, and squash would have died, over 80% of plants eaten by Mayans would have survived a short drought. Over a fifth would have produced food during a year-long drought.

“Even in the most extreme drought situation — and we have no clear evidence the most extreme situation ever occurred — 59 species of edible plants would still have persisted,” Santiago said.

Some of the toughest plants the Maya would have turned to include cassava with its edible tubers, and hearts of palm. Another is chaya, a shrub domesticated by the Maya and eaten today by their descendants. Its leaves are high in protein, iron, potassium, and calcium.

“Chaya and cassava together would have provided a huge amount of carbohydrates and protein,” Santiago said. 

The study may help explain why the Mayan collapse was so patchy, with some archaeologists questioning if it collapsed at all. If droughts hit the crops of the elites, it could explain why so many sites continued after collapse. Sites like Chichén Itzá that continued beyond the Terminal Classic period may have had more flexible rulers.

RESEARCH ARTICLE

Fedick, S.L. and Santiago, L.S. (2021) “Large variation in availability of Maya food plant sources during ancient droughts,” Proceedings of the National Academy of Sciences. doi:10.1073/pnas.2115657118.

Updated 11 Jan 2022 to correct the date from BCE to CE. Thanks to Peter Baker for spotting this.