Author: Murphy, Sinead Flanagan
Improved knowledge of long-term fire regimes and climate-fire-human relationships can play an important role in informing effective management of south coastal forests in British Columbia, Canada. In this study, we used high-resolution charcoal analysis (~17-year intervals) along with strong chronological control (210Pb and AMS-14C age constraints) to provide new mid to late Holocene fire history information for Moist Maritime Coastal Douglas Fir (CDFmm) forests around Somenos Lake on southeastern Vancouver Island and Dry Maritime Coastal Western Hemlock (CWHdm) forests around Chadsey Lake in the central Fraser Valley. Our results indicate that fire frequency at both sites varied throughout the mid to late Holocene, suggesting that CDFmm and CWHdm fire regimes in the Strait of Georgia Lowlands have been non-stationary over the last ~5000 years. In general, fire frequency between the two sites was largely synchronous during the mid to late Holocene, indicating that broad-scale climatic changes were primarily driving fire occurrence in the Strait of Georgia Lowlands during the past ~5000 years. However, a period of asynchrony occurred between 3500 and 2000 cal yr BP when fire frequency was low at Somenos Lake (i.e., the CDFmm site) and high at Chadsey Lake (i.e., the CWHdm site). Neoglacial conditions during this time would have limited fire ignition, thus resulting in low fire activity at Somenos Lake. However, because climate conditions were not conducive to fire (i.e., cool and moist), we suggest that a combination of local scale factors were primarily responsible for high fire activity at Chadsey Lake between 3500 and 2000 cal yr BP. Overall, our results exemplify the spatial-temporal dynamics of fire activity in the in the Strait of Georgia Lowlands during the past ~5000 years and highlight the importance for forest managers to look at the variability of fire occurrence over time and across different sites to disclose the temporal and spatial variability of fire activity and better understand the mechanisms that drive changes.
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