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New Research by Lehman Professor: Deforestation Did Not Cause Collapse of Maya

December 14, 2009

View of the Copan plaza. Photograph by Cameron McNeil.

An archeologist who earned her doctorate only three years ago has shattered accepted scientific thinking about the collapse of the ancient Maya civilization. Research published in Proceedings of the National Academy of Sciences (PNAS), led by Dr. Cameron L. McNeil of Lehman's anthropology faculty, argues that large-scale deforestation did not cause the collapse of the ancient Maya city of Copan in Honduras, as many had believed.

Copan has been widely used and promoted as the archeological "type site"—or model—for the deforestation hypothesis. After analyzing a longer sediment core than the one used to support that theory, Dr. McNeil and her coauthors concluded that the area's forest cover actually increased during the years when the society was collapsing. This finding refutes the popular view that the Maya responded to their growing population and enlarged urban centers by exhausting, rather than conserving, natural resources. Instead, Dr. McNeil suggests, these new data may signal that the Maya were implementing effective techniques of sustainable land use, even as serious problems were undermining the successful governance of Copan and the lives of its people.

View of the Copan Valley with its fertile floor and sloping hillsides. Photograph by Cameron McNeil.

Dr. McNeil is also a research associate at the New York Botanical Garden. Her coauthors are paleoecologists Dr. David A. Burney, the director of conservation at the National Tropical Botanical Garden, and Lida Pigott Burney, the director of the Makauwahi Cave Reserve project.

The Classic Maya civilization encompassed major portions of Mexico and Central America from about A.D. 200 until A.D. 900, when it collapsed and many of its cities were abandoned. A highly advanced civilization, the Maya had a written language, a complex social and political order, densely populated cities, monumental architecture, including temples on pyramidal platforms, and sophisticated astronomical calculations. Anthropologists have advanced various theories about the collapse, including war and drought, but until now deforestation has been viewed as an important factor. This hypothesis has been held up in both archaeological and high school textbooks, as well as in film and literature, such as Jared Diamond's 2005 book Collapse: How Societies Choose to Fail or Succeed, as a lesson of the dangers of our own environmental abuses.

The Petapilla pond is shaped like a donut with a small island at its center with pine trees growing on it. The water is covered with a thick carpet of grasses, cattails, ferns, and orchids. Photograph by Cameron McNeil.

Dr. McNeil and her coauthors agree that forest clearance did occur, based on the ratio of herb to tree pollen measured every 5 cm in the sediment core. High percentages of herb pollen indicate open spaces, whereas high percentages of arboreal (tree) pollen indicate forested space. The new research demonstrates that the first period of deforestation recorded in the sediment core occurred around 900 B.C., when forests were likely cleared due to the wide-scale adoption of agriculture, and herb pollen made up 89.8% of the terrestrial pollen. According to the findings, deforestation again increased around the third century A.D., likely with the arrival of Maya to the Copan Valley and subsequent construction of the Copan Acropolis. The second peak of deforestation likely occurred around A.D. 400, when herb pollen recorded in the sediment core makes up 65.3% of the terrestrial pollen.

The levels of tree pollen found in the sediment core, however, indicate that in the Late Classic period (A.D. 600-900)—the time of the collapse—the area around the city had more forest cover than in the Early Classic Period (A.D. 400-600), with herb pollen making up no more than 40.2 - 29% of the assemblage.

The tephra layer of the Ilopango eruption is composed of volcanic glass. This view of the tephra is magnified 400x. Photograph by Cameron McNeil.

Dr. McNeil's research grew out of her dissertation at The Graduate Center of The City University of New York, where she completed her doctorate in 2006. She first went to Copan in 1999 as a member of the University of Pennsylvania Museum's Early Copan Acropolis Program and sampled more than 40 temple and tomb floors to study the use of plants in ancient rituals. Curious about how ritual plant use reflected the use of the landscape, she extracted sediment cores from five bodies of water in the Copan Valley to understand more about the environmental context of these practices. The sediment core that is the focus of this article was taken from the Petapilla pond near the Copan Acropolis.

Dr. McNeil was assisted in her work by the support of the Instituto Hondureño de Antropología e Historia. Her research was funded by a Fulbright Fellowship and grants from the Foundation for Mesoamerican Research Inc. and Sigma Xi, the national science honor society. Laboratory research was initially conducted at David and Lida Burney's Paleoecology Laboratory at Fordham University and later at the Plant Research Laboratory of the New York Botanical Garden.

Dr. McNeil and two assistants (Obdulio Garza and Rigoberto Morales), extracting a sediment core from the Sesesmil pond, which is also mentioned in the PNAS article. Photograph by Cameron McNeil.

In 2008, Dr. McNeil received the Society for Economic Botany's Mary W. Klinger Award for Outstanding New Book for Chocolate in Mesoamerica: a Cultural History of Cacao (2006), which she edited. More recently, she co-edited The Ch'orti' Area: Past and Present on the Southeastern Maya Periphery (2009), in which she used environmental data to trace human migration to and within the Copan Valley.

Dr. McNeil has conducted archaeological and/or ecological research in every country of Mesoamerica except El Salvador. She is currently working at a site in Guatemala called Tayasal, investigating whether patterns of environmental use similar to those found in Copan are repeated there, and also continuing her work in Honduras at Copan, studying how the ancient Maya living in the valley's hinterlands were supporting the needs of the city.

The article is available in its entirety at PNAS.