Contents

31 August 1990
Vol 249, Issue 4972

About The Cover

A surface fire, near Crown King, Arizona. Low-intensity surface fires have burned repeatedly through ponderosa pine forests of the southwestern United States. Chronologies of fire scars in the tree rings reveal an association between wildfire occurrence in this region and the El Niño—Southern Oscillation during the past three centuries, demonstrating that global-scale climatic patterns affect the frequency of fires and their effects on the ecosystem. See page 1017. [Photograph by John H. Dieterich]