A new study using fire-scarred trees and data collected by University of Arizona tree-ring researchers has documented extensive fire management practices by Western Apache people that significantly reduced the climate's influence on fire activity across their homeland.

The research, led by SMU fire scientist Christopher Roos, analyzed 649 fire-scarred trees from 34 sites in Western Apache traditional territory in central and eastern Arizona and compared them to several thousand trees from the broader Southwest region. The findings, published in the journal Proceedings of the National Academy of Sciences, reveal that despite being a small, mobile population, Western Apache communities had significant control over fire patterns across the landscape at different times of the year, much more than scientists previously thought possible.

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Thomas W. Swetnam, a U of A Regents Professor emeritus and longtime dendrochronologist in the Laboratory of Tree-Ring Research, was a co-author on the study, which relied upon the Tree-Ring Lab's extensive archive of tree cross-sections that provide centuries of the region's fire history. Fire scientists have known for years that Native Americans, and especially the Western Apache, used fire to manage the landscape, based on ethnographic records and interviews with Apache people, Swetnam said.

"It's not news that Native American people used fire to manage the landscape, but the questions have always been where, how much, how frequently, and how specifically did they change seasonal burning patterns," Swetnam said. "What this paper does is it really shows where we can detect the Western Apache people's influence of fire based on their seasonal campsites."

Fires were mainly asynchronous and occurred independently of climate drivers where Western Apache lived seasonally, contradicting previous assumptions that abundant lightning and climate conditions drove fire patterns throughout the region.

Notably, more frequent fires occurred in Apache territory than elsewhere in the region for centuries before the establishment of Indian reservations. Most fires occurred disproportionately in late April and May, when Apache people devoted significant time to subsistence activities in pine forests.

"The fire frequencies were so different in Western Apache homelands that they stood out like a neon light," said Roos, who earned his doctorate from the U of A in 2000 while doing research at the School of Anthropology and the Tree-Ring Lab. "But the fires were also really small, and they were happening at different times of the year, and they were buffering the influence of climate as a result. This was a small group of foragers who were basically taking control of the fire regime. And we were able to show this clearly through tree rings."

The study builds on Roos's previous research that examines cultural burning practices across the Southwest, including work in Pueblo communities and Navajo country. The Western Apache data came from unpublished fire history work conducted 25 years ago, including research commissioned for the San Carlos Apache Tribe.

Roos points out that the findings challenge common assumptions about Indigenous fire management, which often focus on larger, more sedentary populations. The Western Apache were primarily mobile forager-gardeners who practiced limited gardening. Yet, the tree ring evidence shows they maintained systematic control over fire patterns across the landscape. 

According to the study, the Apache fire management created reinforcing cycles of landscape stewardship. Areas they called "farm sites" served as anchors for movement across the territory. Burning in these areas improved forage for game animals. It also enhanced wild plant resources, which brought people back to these locations and led to additional burning cycles.

The research has implications for current fire management approaches. Rather than conducting extensive burns to meet acreage goals, the study suggests that many small, fragmented burns create more effective firebreaks and reduce hazards near human communities.

"We can learn that from tree rings and listening to Native people today, because there's still oral tradition and Indigenous knowledge about the use of fire," said Swetnam, who noted that the paper's co-authors include Nicholas C. Laluk, a researcher with the University of California, Berkeley and member of the White Mountain Apache Tribe who earned his Ph.D. in anthropology from the U of A, and Melinda M. Adams, a University of Kansas researcher and member of the San Carlos Apache Tribe. 

"This is a really great collaboration of western science and Indigenous scientists," Swetnam added.

Other U of A authors involved with the study include Christopher H. Baisan, senior research specialist with the Tree-Ring Lab, and Kiyomi Morino, an assistant research professor of dendrochronology. Authors from other institutions, who also are graduates of the U of A, include J. Mark Kaib with the U.S. Fish and Wildlife Service, and Christopher H. Guiterman with the University of Colorado Boulder and NOAA's National Centers for Environmental Information.