Climatic influences on fire regimes in montane forests of the southern Cascades, California, USA

The relationship between climate variability and fire extent was examined in montane and upper montane forests in the southern Cascades. Fire occurrence and extent were reconstructed for seven sites and related to measures of reconstructed climate for the period 1700 to 1900. The climate variables included the Palmer Drought Severity Index (PDSI), summer temperature (TEMP), NINO3, a measure of the El Nino-Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). Fire extent at the site and regional scale was associated with dry and warm conditions in the year of the fire and regional fire extent was not associated with ENSO or PDO for the full period of analysis. The relationship between regional fire extent and climate was not stable over time. The associations of fire extent with PDSI and TEMP were only significant from similar to 1775 onward and the associations were strongest between 1805 and 1855. PDO and fire extent were also associated during the 1805-1855 period, and ENSO was associated with fire extent before 1800, but not after. The interannual and interdecadal variability of the fire response to temperature and drought suggests that increased periods of regional fire activity may occur when high interannual PDSI variation coincides with warm decades.