Historical diversity of fire regimes across Arizona and New Mexico
Fire regimes shaped forest ecosystems for centuries in the southwestern United States prior to a century of fire exclusion. Tree-ring fire history studies have been vital to our ecological understanding of fire regimes and to inform management. Regional-scale synthesis efforts have revealed the strong connection between fire and climate, but by focusing on coarse-scale patterns over time, such studies may have overlooked finer-scale interactions of fire, climate, vegetation, and human activities. Now, with new tools (burnr and TreeFire), and a plethora of available data (569 sites, 6031 trees, and 44639 fire scars), we examine the diversity of tree-ring fire scar records across Arizona and New Mexico with regard to fire regime metrics and drivers. We found sub-regional patterns of fire-scar seasonality that are likely driven in part by the progression of summer monsoon precipitation, which ends the early-summer fire season. Inter-annual fire-climate relationships varied spatially across the region, but wet years followed by drought were commonly associated with extensive fire. Multi-decadal fire frequency had high spatiotemporal variability, but also contained sub-regional patterns, likely driven by a combination of climate and humans. The synthesis provides a valuable framework for uncovering new spatiotemporal patterns in historical fire regimes and the processes that drive these patterns, which can be used to further inform management and forecast future fire regimes.