August 22, 2012
Deforestation Not a New Problem According To Ancient Maya Studies
April Flowers for redOrbit.com - Your Universe Online
The ancient Maya culture flourished for more than six centuries with more than a hundred city-states scattered across southern Mexico and northern Central America. In A.D. 695, the Maya empire started its slow collapse with the fall of several Guatemalan cities.
Scientists have long thought drought played a part in this collapse, but some recent studies add twists to this long held theory.
A research team led by Benjamin Cook, a climate modeler at Columbia University's Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies, believe the Maya may have made the droughts worse by clearing away forests for cities and crops. This made a naturally dry climate drier.
“We´re not saying deforestation explains the entire drought, but it does explain a substantial portion of the overall drying that is thought to have occurred,” said Cook.
Using population records and other data, Cook and his team reconstructed the progressive loss of rainforest as the civilization grew. They ran computer simulations to see how lands newly dominated by crops would have affected climate.
In the Yucatan Peninsula, which was heavily logged, they found that rainfall would have declined by as much as 15 percent. In other Maya territories, such as southern Mexico, where logging was not as prevalent, the decline was only by 5 percent. Overall, the team attributes 60 percent of the drying estimated at the time of the Maya's peak to deforestation.
Crops like corn replaced the forest's dark canopy letting sunlight bounce back into space. With the ground absorbing less energy from the sun, less water evaporates from the surface, creating less rain-making clouds. This slows down the entire process.
This study, published in Geophysical Research Letters, is not the first to hypothesize deforestation as a means of climate change in the Maya empire. An earlier 2010 study showed that the wet season rainfall could fall 15 to 30 percent if all Maya lands were completely cleared of trees. Robert Oglesby, lead author on the 2010 study, said that the new study numbers of 5 — 10 percent made sense, since Cook's simulation used a realistic tree-clearing scenario rather than a complete deforestation.
The Maya cleared the forests to grow corn and other crops, but they also needed the trees for cooking large amounts of lime plaster used in constructing their elaborate cities.
Thomas Sever, an archeologist at the University of Alabama, Huntsville, and a co-author of the 2010 deforestation study, said that it would have taken 20 trees to produce a single square meter of cityscape. “When you look at these cities and see all the lime and lime plaster, you understand why they needed to cut down the trees to keep their society going,” he said.
The Maya also lacked the technology to tap the groundwater several hundred feet beneath them. Their reservoirs and canals were able to store and distribute water when rain was plentiful, but when the rain failed, they had nowhere to turn.
“By the time of the collapse, every square mile of soil had been turned over,” said Sever.
In a separate study out of Arizona State University, social scientists B.L. Turner and Jeremy A. Sabloff used a revised model of the collapse of ancient Maya to provide an up-to-date, human-environment systems theory where they describe the degree of environmental and economic stress in the Central Maya Lowlands that served as a trigger or tipping point for the society.
Tuner and Sabloff described the Classic Period of the Lowland Maya (CE 300-800) as a "highly complex civilization organized into networks of city-states," in their perspective article published Aug. 21 in the online Early Edition of the Proceedings of the National Academy of Sciences.
Complex interactions between humans and the environment preceding the 9th century collapse and abandonment of the Central Maya Lowlands points to a series of events that have lessons for contemporary decision-makers and sustainability scientists.
These events were a mixture of natural, like climate change, and man-made, including large-scale landscape alterations and shifts in trade routes.
This study agrees with Cook and his colleagues about deforestation being a primary cause. The ancient Maya in this hilly and riverless region confronted long-term climatic aridification and experienced decadal to century-level or longer droughts amplified by the landscape changes that they made, including large-scale deforestation indicated in the paleoecological record.
Previous to the collapse, the Maya occupied the area for more than 2,000 years, noted Turner and Sabloff, "a time in which they developed a sophisticated understanding of their environment, built and sustained intensive production [and water] systems, and withstood at least two long-term episodes of aridity."
The team identifies another cause of the Maya collapse, economic stresses which were probably caused or exacerbated by the droughts.
"This environmental stress was complemented by a shift in commercial trade from across the peninsula to around it, which reduced the economy of the ruling elite to keep up the livelihood infrastructure to prevent the tipping point," said Turner, a Distinguished Sustainability Scientist with the Global Institute of Sustainability at Arizona State University.
"The decision was made to vacate the central lowlands rather than maintain the investment. This theory is not only consistent with the data on collapse but on the failure of the central lowlands to be reoccupied subsequently," said Turner. "It acknowledges the role of climate change and anthropogenic environmental change, while also recognizing the role of commerce and choice."
Sabloff notes that rather than a monolithic period of collapse, there were many variable patterns, which can only be explained by using a complex system view of the culture.
"The Maya case lends insights for the use of paleo- and historical analogs to inform contemporary global environment change and sustainability," wrote the authors. "Balance between the extremes of generalization and context is required."
"Climate change, specifically aridity, was an important exogenous forcing on human-environment conditions throughout the Maya Lowlands," they concluded. "Complex system interactions generated the collapse and depopulation of the (Central Maya Lowlands) and fostered its long-term abandonment. This lesson – increasingly voiced in the literature – should be heeded in the use of analogs for sustainability science."
Today, many of the Maya´s abandoned cities are overgrown with jungle, especially on the Yucatan peninsula. Satellite images, however, show that deforestation is happening rapidly elsewhere, including in other regions the Maya once occupied. These studies may offer a warning about the consequences.