A multi-century perspective on contemporary fire deficit and anomalous fire severity in the southwestern United States

Abstract Wildfires in the southwestern United States are increasingly frequent and severe, but whether these trends are beyond historical norms remains contested. We combine dendroecological records, satellite-derived burn severity, and field measures of tree mortality to compare historical (1700-1880) and contemporary (1985-2020) fire regimes at 406 tree-ring fire-scar sites in Arizona and New Mexico. Contemporary fire frequency is over 80% lower than historical levels. Before 1880, fires averaged 0.87 fires/decade (every 11.4 years), followed by over a century without fire at most sites. Since 1985, the same sites averaged only 0.17 fires/decade (every 58.8 years). Fire severity, however, has increased. At 42% of our sites, centuries-old fire-scarred trees recently experienced anonymously lethal fire severity. Suppressed wildfires tended to burn more severely than prescribed burns and managed “fire use” wildfires. These findings support the expanded use of low-severity prescribed and managed fire to restore ecosystem function and resilience to southwestern dry-conifer forests.