“In Unexpected Places, Clues to Ancient and Future Climate; Warming? Tree Rings Say Not YetDec. 1, 1992
Fires also leave revealing scars in the tree tissue, and if enough trees in a wide enough region prove to bear fire scars at the same time, researchers can guess the year was extremely dry, for aridity invites a blaze’s spread. Studying fire marks in giant sequoias, Thomas W. Swetnam and co-workers have discovered that major conflagrations sweeping across many mountain ranges in California and the Southwest were a long a common feature, occurring at least twice a decade and apparently linked to oceanic currents much farther south, the so-called La Nina events that often result in droughts.
“Finding this synchronicity in fire events was a big surprise to us,” he said. “It tells me that Western landscapes in presettlement era were very smoky places.”
But by the end of the 19th century, settlers seeking to carve out grazing terrain for their livestock had cleared away much of the forest undergrowth that had served as fodder for the fires, and oscillating fire cycles became a thing of the past. So, too, did the long-term vitality and diversity of many forests, and park and wilderness managers are now seeking Dr. Swetnam’s advice on how to recapitulate, in a controlled manner, the synchronous infernos of the past. “We made the forests safe for cattle,” said Dr. Swetnam, “and now we must make them safe for fires once again.”
