Seven hundred years of human-driven and climate-influenced fire activity in a British Columbia coastal temperate rainforest

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.

Ecological legacies of anthropogenic burning in a British Columbia coastal temperate rain forest

“…In perhumid rain forests, climate is assumed to be the primary driver of the distribution and composition of vegetation and lightning‐ignited fires are estimated to occur every few hundred or even few thousand years (Daniels & Gray, ; Lertzman et al., ). Despite these findings, previous research on human and climate drivers of fire activity in our study area indicates that humans may have utilized favourable climate conditions such as periodic extreme droughts to manage resources with fire (Hoffman, Gavin, & Starzomski, ; Macias Fauria & Johnson, ). Although we were unable to determine the exact timing of fire events, ethnographic accounts of intentional burning in nearby areas suggest that burning occurred in the late summer after berries had been harvested and the vegetation was drier (Turner, , ).…”

“…Low‐ and mixed‐severity fires occurred approximately every 39 years for almost six centuries prior to cultural changes in the region in the late 19th and early 20th centuries (Hoffman, Gavin, & Starzomski, ). Because the process of fire scarring is highly variable and dependent on geographical location and fire tolerance of tree species (Tepley & Veblen, ), we provide a minimum estimate of the number of historic fire events (16) and acknowledge that the distribution of fire intervals recorded at the plot level is skewed to fire intervals that are longer than those of the composite MFI expressed at the stand or landscape scale (Table S1.3).…”

“…We completed a fire‐history case study in a historic 287 ha burn located on Hecate Island (N51°39 Latitude, W128°04 Longitude) (Figure ; see also Hoffman, Gavin, & Starzomski, ). This site was chosen for a detailed fire history because it contained abundant, rot resistant and long‐lived (>1,000 years) fire‐scarred trees.…”

“…In these forests, fuel moisture levels rarely drop to the point of ignition and a thick layer of fog often blankets the coastline even in the summer months (Daniels & Gray, ). Despite the seemingly unsuitable conditions for fire, recent research suggests that short‐term summer drought does occur (Hoffman, Gavin, & Starzomski, ) and that fire has been an important component of some forests in this region for millennia, with associated impacts on the abundance, diversity and availability of plant resources (Trant et al., ).…”

“…Fires located on the edges of former habitation sites (Hoffman, Gavin, Lertzman, Smith, & Starzomski, ; Hoffman, Gavin, & Starzomski, ; Turner, ; Wray, )…”