June 5, 1998: Few things are more intriguing than the mysterious disappearances of civilizations, and the Americas have one of the biggest: What happened to the Maya?
About 500 years before Columbus arrived in the West Indies, a thriving civilization peaked in Central America, then seemingly imploded. Theories abound, but the answer appears to be a tragedy that is about to repeat itself - and which can be prevented.
"At the time of their collapse it appears there were no trees and that a major drought ensued," said Dr. Thomas Sever, an archaeologist with NASA's Marshall Space Flight Center. "We're not sure whether these are the result of local or global changes. But we do know that although most of the land is not suitable for farming by today's standards, the Mayan civilization supported one of the greatest population densities ever."
Looking back in time at a dead civilization might seem odd for an agency that usually looks outward to the planets and stars.
"This is quite natural for NASA," said Sever, who works at the Global Hydrology and Climate Center in Huntsville, Alabama. "Archaeology provides important clues - and sometimes, answers - that help us understand how mankind interacts with the environment. You cannot understand a collapse unless you understand the conditions that led to the rise."
That is part of the concern of the government of Guatemala as many of its people systematically burn down the rain forest to make way for farmland that lasts only three years.
The view from space
Realizing that the forests were targeted for major development, the government of Guatemala in the 1980s asked NASA to use its Landsat satellites and other tools to map the rain forests in the Peten region so Guatemala's leaders would know what was left that could be preserved.
Sever and his team worked with images taken by the Landsat Earth observation satellites and by aircraft.
"We were startled by what we saw," Sever said. "You often cannot see borders from space because those are just lines on paper. Landsat showed us rain forest up to a line, then tilled land. That was where Guatemala stopped and Mexico began."
The images made the October 1989 issue of National Geographic and led President Vinicio Cerezo of Guatemala to ask that nation's congress to set the area aside as the Maya Biosphere Reserve (right) in 1990. NASA and the Central American Commission on Environment and Development agreed to a joint research effort.
The results of work by Sever and several colleagues are in Pixels and People, a book published recently by the National Academy Press in Washington. Sever's chapter is "Validating Prehistoric and Current Social Phenomena upon the Landscape of the Peten, Guatemala."
The Peten covers 33,000 square kilometers (12,960 square miles) - a third of Guatemala. Its population includes more than 800 species of trees, 500 species of birds, and large populations of mammals, including monkeys, jaguars, tapirs, and - in rising numbers - humans. It also has alligators, caymans, and small crocodiles, 50 species of coral snake, the aggressive Fer de Lance pit viper whose bite is fatal - if you don't amputate the limb within hours - and tons of ticks.
Finding millennium-old signs of human life in the middle of that is a "missing the forest for the trees" kind of problem. Sever said you could be standing atop an ancient roadway and not see the difference.
Satellite remote sensing helps because human changes to the land are reflected, literally, by vegetation for decades or centuries afterwards. Images from Landsat's Thematic Mapper, a special, multi-color scanner, revealed a number of features, including causeways. This was done by manipulating five channels of data by computer. For example, the ratio of band 4 to band 5 was displayed as green; other combinations were used to make red and blue. The result is called a false-color image that shows one narrow aspect of the truth in a scene.
"These combinations let us identify features more easily," Sever said. "Where the roads cross seasonally flooded swamps - called bajos - the vegetation is more lush than where the dirt is undisturbed."
Even when they find straight lines that indicate a causeway, there's no substitute for getting your hands dirty by excavating the area to confirm that it's a causeway by finding compacted soil plus bits of trash, ancient pot shards and other debris left by humans.
Secondhand Eden
"At first glance, the undeveloped areas of the Peten look untouched," said Sever, who has visited the area several times. "It's actually a regenerated rain forest, one that had recovered from human abuse a millennia ago. The tragedy is that now the story is about to repeat itself. The lessons from this activity can portend what may happen to other developing nations that are destroying forests for short-term economic gain."
The period of interest is not just the collapse of the Mayan civilization, but the centuries before when it it rose and was stable.
From 250 to 900 C.E. (current era) was the Classic Mayan period which saw the building of many cities centered on temples and ball courts (stemming from their creation beliefs) and connected by extensive road systems. The Peten region had one of the densest human populations of any time in human history: almost 1,014 persons per square kilometer (2,600 persons per square mile) in the cities, and from 20 to 50 percent as many in the rural areas.
Then they just disappeared, in the space of 100 years, perhaps as fast as 20 years," Sever said. "From 830 to 930, the population plummeted by two-thirds, and continued to decline for centuries afterwards. It nearly reached zero in the 1800s."
It may be one of the greatest demographic disasters in human experience.
Swamp islands
One of the mysteries is how the Maya fed a population that was too great for the land to support. The Mayan population had already exceeded what the land could support by the year 300, yet they continued to grow for another 500 years as population densities increased up to tenfold.
"We do not understand how they could feed themselves," Sever said. "We think that the bajos - covering about 40 percent of the land - are the reason."
Bajos are seasonally flooded swamps that readily show up on satellite images.
The natives told Sever and his team that what satellite imagery perceived as three types of bajos were actually seven types. Of those, two or three are moist enough during the dry season to support agriculture, thus adding to the land that the ancient Maya could till.
And on the wooded "islands" rising at various locations in the bajos, archaeologists usually find Mayan ruins and artifacts, indicating that the bajo somehow played an important role in their lives.
Field work suggested that virtually all of these islands were occupied by "bajo communities." Whether they were long-term communities or the result of sudden, brief occupation is being studied, and may be critical to understanding how the Mayans adapted to the rain forest in the Precolumbian era.
Part of the challenge, Sever said, is that no records exist of how the Maya lived.
"Everything - pottery, stone carvings, other artifacts - depicts their religious life and beliefs, and their military and political events," he explained. "Nothing depicts everyday life, so we don't yet understand the relationships of bajo communities to the whole fabric of Mayan society and economy."
Still, if bajo agriculture worked well, why did Mayan civilization collapse after the population had declined somewhat and thus placed less demand on the land?
"The collapse took a terrible toll on this society," Sever continued. "We see evidence of houses and temples falling into disrepair, of a people living in something like you would see in a post-apocalypse movie." Healthy Mayan society regarded houses and temples as living things that had to be fed and maintained. After the collapse, that ended, and the survivors treated buildings as shelters. The evidence even indicates that the survivors could no longer read the glyphs made by their fathers and grandfathers.
Scorched earth
So what happened?
The disappearance of trees may be a clue. A climatic change that dropped the water table would also dry up bajos used for agriculture. In turn, that would force the Mayans to carve out farmland from the jungle.
Despite its broad diversity of life, the rain forest is life on the edge. It does not have deep soil in which life can root itself. Instead, the survival of the rain forest depends on a frenetic recycling of everything.
"Land that is converted from jungle to farm will have a 100 percent crop yield the first year, 40 percent the next year, and even less the third," Sever explained. "So, the farmers move on and convert more jungle to farmland. But the wasted land does not recover for hundreds of years. Eventually, the farmers will destroy their way of life."
For now, though, deforestation rather than adaptation is the rule for the descendants of the ancient Mayans. Ironically, peace is partly to blame. The people had repopulated the area to a modest level, and at least since 1720 the area had a stable society.
It was opened to development by the Guatemalan government in the 1960s, and effectively closed by civil war in the late 1970s and '80s. At the same time - 1960 to 1986 - the local population ballooned from 26,000 to more than 300,000. In January 1997, though, the government and rebels signed a truce which included allocation of land for farming in the Maya Biosphere Reserve.
Development in the preserve ranges from slash-and-burn agriculture to selective logging of mahogany, capturing endangered animals for sale abroad, archaeological looting, and marijuana production.
"We used Landsat images to measure the 'greenness' of the Peten," Sever said. "Basically we subtract one image of vegetation from an older image of vegetation. The result is an alarming picture of where trees are gone."
One thing they have discovered is that 90 percent of deforestation happens within 2 km (1.2 mile) of a road. An illegal pipeline - discovered in a Landsat image - has provided a new route through the heart of the jungle.
A troubling diagnosis
"It's like watching blood vessels grow so a tumor can move forward and consume tissue," Sever said. "The rates of deforestation are not constant across the Peten. We can see areas where it is almost absent, like Carmelita in the central Peten where traditional farming is practiced, and Tikal, where guards are on duty.
"One of the really troubling aspects is that we can also see islands of forests left when people settle an area or when a pipeline is built. We're not sure how this affects the animals and their feeding and mating territories, or how it might isolate and strangle their genetic diversity."
Satellite imagery makes this work easier in more ways than just providing quick pictures of the study area. They help Sever and his colleagues give the local citizens a new view of their homeland and a better sense of ownership.
"We always take lots of copies of the Landsat images and leave at least one with each village we visit," Sever said. "This takes away some of the mystery and fear because we share what we know and make the local leaders a part of our work. In time, word spreads and people become more willing to support us and help interpret local features that we can't quite make out in the pictures."
This is especially important because the area is poorly mapped. Satellite images and GPS data often do not match what is found on the ground. Features may be kilometers out of place, or might not exist at all.
El Niño's possible role
Sever's studies of the Peten area continue with new urgency caused by fires burning large areas of rain forest in the wake of El Niño extending the dry season. This raises the question of whether El Niño events a thousand years ago may have played a role in destroying the Mayan peoples.
How much damage is being done by now will not be known until the fires end and the smoke clears so satellites can see the area again.
"We don't know yet because we don't know that much about the history of El Niño," Sever said. "We have some evidence in Peru that the Incas went through extended periods of drought that may have been influenced by El Niño. Because the rain forest recycles everything very quickly, it will be hard to find clues like tree rings in old-growth forests. But what is happening to Central America now could certainly be a good model of what happened to the ancient Maya. History seems to be repeating itself. We have to convince enough people of the lessons before it's too late." ."
Teamwork
Little in modern science is done by one person alone. This is especially true of archaeology. While most of this story focuses on Dr. Thomas L. Sever, he is the first to point out that his work was made possible by working with several colleagues, including:
James Nations, an anthropologist and ecologist at Conservation International,
Santiago Billy, a citizen of Guatemalan and a conservationist working with Conservation International,
Dr. Frank Miller, a forester at Mississippi State University,
Daniel Lee, a geographic information systems (GIS) expert at GeoTek,
Also joining this effort were Dr. Patrick Culbert, an archaeologist at the University of Arizona and Dr. Steven Sader, a forestry expert at the University of Maine.