Defenestrating deforestation

2 minute read

Lots of people have written about the collapse of the ancient Maya, often as some kind of “lesson” about how present-day society needs to change for its own survival. A recent theme, pushed by Jared Diamond in particular, but also others, has been that the Maya failed to manage natural resources sustainably. Their political structure couldn’t deal with the growth of their population, and short-term decision-making led to ecological collapse.

Well, it’s easy enough to propose such a sweeping hypothesis, but devilishly hard to test it. And so it’s easy to forget that it is just a hypothesis.

In the early bin at PNAS, McNeil and colleagues report on a test of the hypothesis for one locality, Copan, Honduras:

Archaeologists have proposed diverse hypotheses to explain the collapse of the southern Maya lowland cities between the 8th and 10th centuries A.D. Although it generally is believed that no single factor was responsible, a commonly accepted cause is environmental degradation as a product of large-scale deforestation. To date, the most compelling scienti?c evidence used to support this hypothesis comes from the archaeological site of Copan, Honduras, where the analysis of a sediment core suggested a dramatic increase in forest clearance in the Late Classic period (A.D. 600900). By contrast, in the work presented here, the authors analysis of a longer sediment core demonstrates that forest cover increased from A.D. 400 to A.D. 900, with arboreal pollen accounting for 59.871.0% of the pollen assemblage by approximately A.D. 780980. The highest levels of deforestation are found about 900 B.C. when, at its peak, herb pollen made up 89.8% of the assemblage. A second, although less pronounced, period of elevated deforestation peaked at approximately A.D. 400 when herb pollen reached 65.3% of the assemblage. The ?rst deforestation event likely coincided with the widespread adoption of agriculture, a pattern found elsewhere in Mesoamerica. The second period of forest clearance probably was associated with the incursion of Maya speakers into the Copan Valley and their subsequent construction of the earliest levels of the Copan Acropolis. These results refute the former hypothesis that the ancient Maya responded to their increasingly large urban population by exhausting, rather than conserving, natural resources.

I admire this kind of close empirical work – identifying pollen in sediment cores may not be glamorous, but it’s maybe the best way we have to document human impact on these ecologies.

References:

McNeil CL, Burney DA, Burney LP. 2009. Evidence disputing deforestation as the cause for the collapse of the ancient Maya polity of Copan, Honduras. Proc Nat Acad Sci USA (online early). doi:10.1073/pnas.0904760107