Altogether elsewhere, vast / Herds of reindeer move across / Miles and miles of golden moss, / Silently and very fast.
--W.H. Auden, from "The Fall of Rome"
I worked with international dendrochronologists for this series, culling source images of tree ring cross-sections from studies connecting climate variability and periods of human instability. The events represented in this series—the Fall of the Roman Empire, the Aztec Conquest, the Black Death, and Anasazi migration in the 12th century—correlate to periods of drought recorded by the tree rings. The tree rings (and hence the tree) are a stand-in for empire while being, as W.H. Auden puts it, "altogether elsewhere."
I chose singular tree ring images to represent larger, comprehensive studies. The shifting thread color mirrors and highlights historical events. As the Roman Empire begins to fade and the Barbarian Invasions or Migration Period is set in motion, white thread turns to gray then black as the tree ring density increases with the corresponding drying period; during the Aztec Conquest the drought cycle is much more compact and intense along with the accompanying events so the contrast in thread color is that much more abrupt; for the Anasazi migration during the 12th century, the thread color transitions in rolling waves paralleling wet and increasingly prolonged dry spells.
Drought cycles act as a catalyst. A span of dry years followed by a string of wet winters may lead to a rat population spike and hence an outbreak of plague. Or, drought can result in crop failure that precipitates social instability. However independent we humans like to imagine ourselves, the fate of civilization has always been tied to the realities of nature.
I gained access to images of tree cross-sections thanks to the generosity and support of four outstanding dendrochronologists each doing amazing work in their field:
Ulf Büntgen together with Daniel Nievergelt at the Swiss Federal Research Institute WSL; Jose Villanueva-Diaz at the National Research Institute of Forestry, Agriculture and Livestock, Gómez Palacio, Mexico; Pearce Paul Creasman, Laboratory of Tree-Ring Research, University of Arizona. All answered my endless e-mails with enthusiasm and receptivity. I cannot thank them enough.
Ulf Büntgen is the lead author of "2500 Years of European Climate Variability and Human Susceptibility" that became the spark for this series (published online in 2011 by the journal Science).