A team of scholars led by University of Cincinnati professors Nicholas and Vernon Scarborough found evidence of a major environmental transformation that helps to explain a puzzle that has stumped Maya scholars for decades. Why would the Maya live in an area where the primary water source is little more than mud half of the year?
The discoveries reveal why many early Maya centers were abandoned about 1,600 years after the civilization first appeared in the lowlands of Latin America. They also document why the Maya moved to new areas where they created elaborate water storage systems that allowed their civilization to thrive for several more centuries.
Dunning, a geographer, and Scarborough, an anthropologist, both in the UC McMicken College of Arts and Sciences, are joined by four co-authors in the report of their research in the latest issue of Annals of the Association of American Geographers (Volume 92, No. 2, 2002) .
The plight of the Maya, a Native American society that built densely populated cities of towering pyramids and then abandoned them, has been an unresolved mystery for scholars around the world. The first Maya settlements appeared about 2000 B.C., but by 950 A.D. most of the lowland cities were unpopulated. The once-thriving Maya cities were overgrown by tropical forests until archaeologists began to rediscover them in the mid-19th century.
Many of the early centers were located near "bajos" - large depressions in the limestone bedrock. This presents another riddle that has "bugged scholars in the Maya area for years," Dunning says. Why? Because today these swamp-like depressions, or bajos, are wet only from about July to November. That makes them unsuitable to support a large populace.
The two UC scholars and their co-researchers have discovered that these bajos were once perennial wetlands or shallow lakes. About 400 B.C. to 250 A.D., human interference, climate and environment combined to transform them into seasonal swamps.
"These hydrologically stable ecosystems were potentially a more attractive settlement location than the seasonal swamps found there today. We argue that human-induced environmental change, in tandem with climatic change, transformed at least some of these bajos between 1,700 and 3,000 years ago," the co-authors write.
They term this dramatic transformation "one of the most significant and long-lasting" human-induced environmental changes "ever documented in the pre-Columbian New World."
The team bases their conclusions on data collected during on-site investigations near La Milpa in northwestern Belize, in 1997 and 1998, and between Yaxha and Tikal, in northeastern Guatemala, in 1999. They studied topography, hydrology, soil, vegetation and cultural features. They analyzed numerous sediment samples, taken from bajos and trenches.
What they found was that beginning in about 100 A.D., most of the surface water in these bajos disappeared. Several feet below the bajos' surface stands a layer of wetland peat, containing evidence of pollen from trees, aquatic plants and corn. But at the end of the Preclassic era, this layer was buried in layers of clay sediment.
Judging from these layers, the team says, farming began to deforest the landscape as the Maya population escalated. With the forest cleared, erosion accelerated. Rain carried sediment into the bajos, where "they would become plugged up," said Dunning. "They were basically fragile environments to begin with. We think it was a combination of natural climatic change and human interference, but the Maya were probably the biggest culprit with the deforesting of the landscape and widespread quarrying to construct their cities."
As profound as the bajos' transformation was, however, the researchers note, "It is equally remarkable that in many areas the Maya not only successfully adapted to, but flourished in the altered environment throughout the Classic period." These changes help explain why some early Maya urban centers were abandoned near the end of the Late Preclassic period (400B.C.-150 A.D.), and others adapted elaborate water-storage systems.
At the end of the Pre-classic period, one of the most notable changes occurred with the abandonment of El Mirador, Nakbe and nearby urban centers, the scholars write. "It is possible that their large populations made them particularly vulnerable to environmental disturbance, including prolonged drought. Or perhaps because of their great size, environmental degradation was more severe or rapid than in neighboring areas, thereby triggering abandonment."
In many places, like La Milpa, the loss of perennial water sources in the bajos led the Maya to develop new water sources and more water-conserving farming methods to help them make it through the dry seasons. "Thus it is not surprising that during the transition from the Preclassic to the Classic, reservoirs became an integral part of the urban landscape at many Southern Lowland centers," the scholars write.
The authors stop short of concluding that all - or even most - interior bajos in the southern and central Maya Lowlands contained perennial wetlands at some point in their past. But they say, "evidence to that effect is mounting." Their report focuses on 42 trenches and test pits in five bajos. They call for more research to settle the issue and plan to look at more and bigger bajos in northwestern Belize in the near future.
While their studies help to answer questions about the past, the authors stress their work also holds important lessons for the present and the future, namely that of "slash and burn" farming and other activities that are destroying today's rainforests. LaMilpa is part of a conservation district, so it remains largely forested. But the forest near Yaxha, outside the border of a preserve, is being cleared at a rapid rate.
Dunning says that when he first arrived in the southern area of Guatemala's Peten rainforest in the early 1990s, the landscape there was 80-90 percent forest. Today, it's more like 80-90 percent cleared land.
"Our findings demonstrate the potentially devastating and long-term consequences of tropical deforestation," the scholars warn. They also note that the transformation of bajos from perennial to seasonal wetlands occurred about 2000 years ago, and despite the passage of centuries, the bajos have never fully recovered.
Dunning, Scarborough and Fred Valdez Jr., who is a faculty member at the University of Texas at Austin, are also at work on a book on the political economy of the ancient Maya, due out in 2003.