Abstract
While wildland fire is globally most common at the savannah-grassland ecotone, there is little evidence of fire in coastal temperate rainforests. We reconstructed fire activity with a ca 700-year fire history derived from fire scars and stand establishment from 30 sites in a very wet (up to 4000 mm annual precipitation) temperate rainforest in coastal British Columbia, Canada. Drought and warmer temperatures in the year prior were positively associated with fire events though there was little coherence of climate indices on the years of fires. At the decadal scale, fires were more likely to occur after positive El Niño-Southern Oscillation and Pacific Decadal Oscillation phases and exhibited 30-year periods of synchrony with the negative phase of the Arctic Oscillation. Fire frequency was significantly inversely correlated with the distance from former Indigenous habitation sites and fires ceased following cultural disorganization caused by disease and other European impacts in the late nineteenth century. Indigenous people were likely to have been the primary ignition source in this and many coastal temperate rainforest settings. These data are directly relevant to contemporary forest management and discredit the myth of coastal temperate rainforests as pristine landscapes.
Highlights
While wildland fire is globally most common at the savannahgrassland ecotone, there is little evidence of fire in coastal temperate rainforests
There has been very little documented evidence of historic fire activity in coastal temperate rainforests located in the Pacific Northwest (PNW) and previous disturbance studies have asserted that both human- and lightning-caused fires are infrequent and become progressively rarer in high-latitude regions [13,14,15,16]
Wildfire occurrence is influenced by variability in modes of sea surface temperatures (SSTs) such as the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) that influence winter temperature and precipitation patterns and indirectly affect summer moisture availability [22,23,24]
Summary
While wildland fire is globally most common at the savannahgrassland ecotone, there is little evidence of fire in coastal temperate rainforests. A handful of studies in coastal temperate rainforests of British Columbia have described temporally coarse reconstructions of Holocene fire activity with charcoal stratigraphy in lake sediments [18] and radiocarbon dating of soil charcoal [19,20,21] These studies depict patchy fires during the last few centuries embedded within landscapes experiencing long (sometimes more than 1000 year) fire intervals as well as widespread increases in fire activity in the Mid- and Late Holocene [19,20,21] that may be related to increases in the use of fire by Indigenous peoples [21]. The PDO is characterized by variations in SSTs in the North Pacific and positive (negative) PDO values produce relatively similar climate and circulation patterns to El Niño (La Niña) conditions though the periodicity is decadal (approx. 20 years) [26]
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