10,000 Years of Fire History, Forest Composition and Climate Change in Coastal British Columbia, Canada

In recent years, forests in western Canada have been burning more frequently and over larger areas. In British Columbia, 2017 and 2018 were consecutive record-breaking years in terms of total area burned. Understanding the dynamics between fire regimes, forest structure and composition, and climate is becoming increasingly important as climate continues to trend towards warmer and drier conditions. Contiguous charcoal analyses were performed on a 9 m long lake sediment core from the Gulf Islands National Park Reserve in southern British Columbia to reconstruct fire history over the last 10,000 years. CharAnalysis was used to interpolate the dataset to a median sample resolution of 13 years and calculate charcoal accumulation rates for inferring fire events. Over the last 10,000 years, the mean fire return interval (mFRI) was 142 ± 28 years with a total of 71 identified fire episodes. Fires were more frequent between 10,000 and 7500 cal yr BP, when summer climate was both warmer and drier, and 27 fires events were recorded resulting in a mFRI of about 90 years. Through the mid- and late Holocene, as climate cooled and seasonality decreased, fire frequency decreased to a mFRI of nearly 200 years between each fire episode. Pollen analyses on the same sediments show that forests have been dominated by Douglas-fir for much of the Holocene, giving more weight to climate as the main driver of change in fire regimes rather than changes in vegetation composition. As fire management practices shift from fire suppression to more sustainable practices including prescribed burning, this study offers the Gulf Islands National Park Reserve important baseline information on the areas natural fire regimes and their links to changes in climate that can help guide future conservation efforts.