Climatic and human influences on fire history in Pike National Forest, central Colorado

We investigated interannual and multidecadal variability in fire regimes, as related to climate and human land-use in Pike National Forest, central Colorado. Short and longterm trends in fire-scar records were related to tree-ring proxy records of moisture availability and to variability in El Ni?o - Southern Oscillation (ENSO). Fire occurrence is strongly tied to interannual drought conditions and is associated with cycles of ENSO. Fire events tend to occur in years of reduced moisture availability (La Ni?a years) and are often preceded by 2-4 years of increased moisture availability (El Ni?o years). A period of reduced variability in the tree-ring record from 1760 to 1820 AD, roughly corresponds to a period of reduced fire occurrence from approximately 1792 to 1842. Coincident with increased fire occurrence, variability in the climate proxies was high in the middle to late 1800s until the early 1900s. Multidecadal impacts through land use are also evident in the fire record with sharp increases during EuroAmerican settlement in ca. 1850 and abrupt declines with the start of active fire suppression after ca. 1920. Both humans and climatic variation appear to have interacted synergistically to create long-term trends in fire occurrence over the past two centuries.