by Melanie Titanic-Schefft
photos by David Lentz

Droughts and climate change led to the eventual abandonment of Tikal, a major Mayan city of affluence that thrived for about 1,500 years in present-day Guatemala.

According to University of Cincinnati research just published in the prestigious Proceedings of the National Academies of Sciences (PNAS), effective and sophisticated land-use practices sustained the thriving Mayan city of Tikal for more than 1,000 years until drought and climate change led to the abandonment of the city, which was once home to tens of thousands of people at its peak in A.D. 700.

Those are the findings of David Lentz, UC professor of biological sciences in the McMicken College of Arts and Sciences, and his colleagues. They analyzed surveys, satellite imagery, archaeological information, water, food and forest resources and pollen data at Tikal to establish the timeline and causes of its rise and subsequent demise of the prominent Mayan city. Their paper, “Forests, Fields and the Edge of Sustainability at the Ancient Maya City of Tikal,” is in the December issue of PNAS.

Faculty and student members of that research team are from UC, the University of Texas, Carnegie Mellon University, NASA, Brigham Young University and the Instituto de Antropologia e Historia and include: David Lentz, Nick Dunning, Vern Scarborough, Ken Tankersley, Silvia Alvarado, Walter Burgos, Sheryl Carcuz, Chris Carr, Mauricio Diaz, Rob Griffin, Angela Hood, Brian Lane, Raquel Macario, Blanca Mijangos, Kim Thompson, Eric Weaver, Thomas Sever, Liwy Grazioso, Carmen Ramos and Richard Terry.

Flourishing city clears way to its own demise

Archaeologists divide Mesoamerican development into three major time periods: 

• PreClassic or Formative period extending from B.C. 1500 - A.D. 300

• Classic period extending from A.D. 300-950 

• PostClassic period extending from A.D. 950-1521

Says UC’s Lentz, “Our goal is to understand how the Maya lasted as a highly complex society for well over 1,500 years in a tropical environment. Their resource needs from forests were very great because they used trees to construct monumental buildings, for the creation of plaster (which was a surface cover for buildings and roadways), for cooking and many other needs. They had a sophisticated, long-lasting management system that apparently began to go awry during the Late Classic period” (A.D. 600-950).

Tikal’s population grew and prospered via their agricultural proficiency, including irrigation, terracing and slash-and-burn cultivation, along with controlled agroforestry and water conservation techniques. However, when Lentz and his team investigated mineral deposits in regional caves to try and understand the city’s demise, they found remarkable evidence for unusually persistent episodes of low rainfall during the ninth century that corresponded with the abandonment of Tikal.

Lentz credits this skillfully managed ecosystem for sustaining a large preindustrial community. However, the self-sustaining and effective land-use eventually resulted in the reduction of a consistent annual rainfall that was necessary to sustain their lives. In other words, human activity in the form of intensive agriculture and deforestation reached a tipping point, causing prolonged drought.

That’s because in spite of elaborate irrigation, the Maya eventually cleared about 60 percent of their forest, which had a dramatic impact on the moisture in the air. Because rain forest density creates conditions for high humidity and rain, the subsequent depletion of those forests caused a corresponding decrease in moisture and rainfall. This subsequently contributed to drought and thus, the depletion of vital water reservoirs in a climate where rain was a valuable resource, common only during the winter rainy season.

Food, fuel and land use

Lentz estimates the population of Tikal at about 45,000 by the amount of fuel and food they had.

Looking at pollen data and soil levels around the perimeter of the city, the UC team discovered that by the Late Classic Period, Tikal’s forest areas were reduced by 60 percent of the approximately 1,100 square kilometers of total land available. The crop fields used to grow maize (corn) and bajo was about one third of the available land and the rest was used as an urban area where they lived.

Closely examining soil and rock samples, Lentz and colleagues’ research revealed that, at first, the Maya managed their forests well, cutting down only a few trees at a time and replacing them as they went. For many years they had a viable conservation system, however, the UC scholars point out through their research that the Maya later made several mistakes that eventually caused problems with erosion.

“But then, as they moved into the classic period, they somehow figured out ways to control erosion because the erosion was a lot less during the classic period, which shows that they developed a lot of techniques for protecting their environment,” says Lentz. “And these behaviors kept that city going for over a thousand years.”

Agroforestry

Using forest growth data, Lentz was able to determine how the Tikal forest supplied essential resources such as wood for fuel and construction material, habitat for game and wild plant food for pharmacopoeia from medicinal species.

Sectioning off six hectares (10 acres) of the rain forest, Lentz and his students marked and measured each tree to determine how much of the forest had to be managed on a sustainable basis. They found that the most commonly used trees were:

• Inkwood - used for burning, later commercially extracted by the British in the 18th and 19th centuries to be used to make dye
• Chicle tree - used for building

The Tikal fields were used to grow maize and a variety of other crops and, as Lentz points out, as in a lot of places, a city often grows on the best land, so the Maya also grew orchards and kitchen gardens around their houses.

Using the Late Classic village of Cerén as a comparative model, Lentz and colleagues showed that Tikal operated on a much larger scale, but used essentially the same array of crops. Tikal grew maize, three species of beans, two species of squash and several species of root crops, including sweet potato. The Maya at Tikal also used the margins around the swampy areas called bajos to grow what they could during the dry season.

Tikal grew as a city around a system of springs emanating from what is now the Temple Reservoir. The temple sits at the head of a long ravine that was blocked off in places to impound the water that flowed from the springs. As Tikal continued to grow, they built large plazas on either side of the ravine and canted the pitch of the pavements so that seasonal rainwater would flow into the reservoirs.