Cover image: Pictured is a Siberian pine on the Khorgo lava field of central Mongolia. Dubbed the Logo Tree, the long-dead tree alerted the authors to the potential for finding ancient Siberian pine trees across the lava field. Neil Pederson et al. created a tree-ring–based record of moisture extending back more than 1,000 years from living and dead pines to reconstruct the drought history of Mongolia. The authors discovered a period of high moisture between 1211 and 1225 CE, during the reign of Genghis Khan. Enhanced grassland productivity due to the moisture likely provided Khan's empire with the energy and resources necessary for expansion. See the article by Pederson et al. on pages 4375–4379. Image courtesy of Neil Pederson.