Historical fire-climate relationships of upper elevation fire regimes in the south-western United States

Understanding relationships between variability in historical fire occurrence and ocean-atmosphere oscillations provides opportunities for fire forecasting and projecting changes in fire regimes under climate change scenarios. We analysed tree-ring reconstructed regional climate teleconnections and fire-climate relationships in upper elevation forests (>2700 m) from 16 sites in eight mountain ranges in the south-western USA. Climate teleconnections were identified by testing for associations between regional Palmer Drought Severity Index (PDSI) and individual and combined phases of El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) indices for both the fire exclusion (1905-1978) and reconstructed fire periods (1700-1904). Fire-climate relationships were identified by comparing reconstructed fires (84 fire years) in three classes (all, synchronous and stand-replacing fires) with PDSI, precipitation, temperature, and individual and combined phases of ENSO, PDO and AMO indices. Individual and phase combinations of ENSO, PDO and AMO were associated with variability in regional PDSI. Upper elevation fire occurrence was related to variability in regional drought, ENSO phase and phase combinations of ENSO and PDO. We conclude that ENSO most consistently influenced variability in moisture and upper elevation fire occurrence, including stand-replacing fires, but this relationship was potentially modulated by phases of the PDO.