In the spirit of Satiable Curiosity, which discussed just-growed stories.

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 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 59.8–71.0% of the pollen assemblage by approximately A.D. 780–980. 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 first 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.

Empirical research is necessary but not sufficient. It helps test old hypotheses and develop new ones, but they need testing too. This old post discussed pollen and the "dominant deforestation narrative" as it is called.

The dominant deforestation narrative is that the plains were once forested in the ice age and post ice age period before humans arrived, and that humans burned them down to make a hunting park. The prairie and bison biome Eurasians saw when they arrived was a created environment.

This view was supported by analysis of lake sediments that showed large quantities of pine pollen from that era. The deforestation myth was supported. But there was too much pine pollen, a greater percentage than we find in a real pine forest since there are other forest floor species that contribute pollen too. This was ignored since the dominant deforestation narrative was served . . .

Later work grappled with the broken data, trying to answer the open questions, and found that pine pollen persists well due to a waxy coating while pollen from grasses and forbs does not. Digging in unweathered places revealed that there were few pine trees and that the great plains was a sagebrush grassland in ice age times. The prairie evolved from that grassland, and though there are different species now they are similar grassland species.

And so, my first reaction to the Mayan collapse hypothesis based on pollen counting was to wonder if differential weathering or some other sort of factor had skewed the data, or if there was something atypical about the location where the sediment cores were taken? Perhaps some future investigator will discover that our stories still have flaws. I am extra suspicious of this sort of research since it is political ecology, the use of scientific hypotheses to advance political objectives.

Perhaps the most interesting piece of political ecology that has been produced thus far is the work of James Fairhead and Melissa Leach, who challenge some prevailing notions of environmental degradation in Africa. Along the border between the Sahelian savanna and the tropical rain forests in west Africa, we find numerous patches of forest amid grassland. The prevailing notion among government and development agency personnel was that human activity had destroyed large swaths of forest, turning it into savanna through indiscriminate burning, farming, and overgrazing. They rushed to slap restrictions on the use of the remaining bits of forest, hoping to preserve them from destruction by limiting human activity.

Through some careful use of historical sources, Fairhead and Leach found that just the opposite was true. The areas in question were "naturally" pure savanna, and human activity had created the forest patches.

It's not wise to believe that what is going on, what went on, or what will happen is known. We have stories that we tell ourselves that encapsulate some of the evidence we have gathered, but we may not have good evidence or understand it properly.