Is Climate Change Restoring Historical Fire Regimes across Temperate Landscapes of the San Juan Mountains, Colorado, USA?

Abstract

Wildfires are increasing with human-induced climate change, but could this be ecologically beneficial in landscapes where recent fire is deficient relative to historical? I compiled 1980–2020 fire data for the San Juan Mountains, Colorado. I analyzed fire sizes and trends in area burned and fire severity, and compared fire density and rotations between 1980–2010 and 2011–2020 among ecosystem types and watersheds. I compared historical (pre-industrial) evidence from tree-ring, charcoal, and land-survey reconstructions to evaluate whether recent fire is outside the historical range of variability (HRV). Nearly all burned area was in the southwestern San Juans in 5 of 41 years and 35 of 4716 wildfires. Between 1980–2010 and 2011–2020, fire densities increased ∼200% and rotations shortened to ∼25%, similarly among ecosystems and watersheds, consistent with climatic effects. Fire rotations in 2011–2020 were within HRV for three ecosystems and deficient for four. Fire sizes and severities were within HRV. Moderate- and high-severity fire had no significant trend. Thus, reducing fire size or severity is currently ecologically unnecessary. Instead, incorporating fire from climate change, via wildland fire use, supplemented by prescribed burning, could feasibly restore historical fire regimes in most San Juan landscapes by 2050, the target of the Paris 1.5 °C goal.