Message #227446

[Raven]

Stahle and his team used data from 74 core samples extracted from 30 specimens of millennium-old Montezuma baldcypress trees (Taxodium mucronatum) growing in the canyon of Amealco, Queretaro — only 90 kilometres (56 miles) away from Tenochtitlan, capital of the Aztec empire, and 60 km (37 miles) north-east from Tula, the Toltec state’s main city. Stahle says this tree species, related to North American sequoias, is the only plant in Central America that frequently lives up to one thousand years or more.

“This is the national tree of Mexico, and it tells such an interesting story of the decline of the Mexican empires”, says Stahle, adding that previous tree chronologies for Mexico were only three to four centuries long. “This is the first one that goes back into pre-Hispanic times,”

The researchers determined the year of formation for each tree ring and analysed what the rings’ growth patterns had to say about how soil moisture varied from growth season to growth season over the years, a parameter directly associated with rainfall. “The beauty of tree rings is that they’re annual: you get an estimate for wetness for every single year — you don’t get it from other archives, not as precisely,” Stahle says.

“This research… highlights the role fine-grained climate data can play in helping us understand the trajectories of past human societies,” says David Anderson, an archaeologist at the University of Tennessee, Knoxville who was not involved in the new study. “This study will prompt a great deal of follow-up research by archaeologists and palaeoclimatologists alike, and offers lessons for our own civilization — specifically how vulnerable complex societies may be to drought-induced crop failures.”

This research received funding from the National Science Foundation’s Paleoclimatology Program and the Inter-American Institute for Global Change Research.

http://www.pasthorizons.com/index.php/archives/02/2011/infomation-from-long-lived-mexican-trees-pinpoint-four-ancient-megadroughts