Influence of Humans and Climatic Variability on Historic Wildfire Dynamics in Jasper National Park, Canada

We reconstructed wildfire history from fire-scars to detect the influences of climatic variability and land-use change on wildfire dynamics in the lodgepole pine (Pinus contorta var.  latifolia Engelm.) forests of Jasper National Park in the Canadian Rocky Mountains.  New original analyses were performed on 170 cross-section samples collected in the 1970s from 52 sites around Jasper, Alberta.  The updated fire record reveals that fire occurrence was highly variable: site-level mean fire return intervals ranged from 4.9-52.5 years.  Fire activity (i.e.  fire size and frequency) decreased through time, with fire exclusion becoming widespread during the 1950s.  Along with less fire activity on the landscape, there were also shifts in fire seasonality from mostly spring burns that were probably intentionally ignited by First Nations to summer fires that are probably caused by a combination of lightning and accidental ignitions (p<0.05).  While most fires were localized and seemingly driven by topographic controls, the 18 widespread fires (events occurring across at least 10% of sites) were primarily driven by dry and warm climatic conditions, often associated with El Niño events.  Large regional fires burned across almost all sites, although some remnant patches remained unburned, suggesting a historically mixed-severity fire regime.  This fire history is distinct from an adjacent region, where there is very limited public access, where there have been almost no fires since ca. 1925.  To be consistent with historic patterns, large-scale restoration via prescribed burning should be scheduled to promote a frequent, patchy, and mixed-severity wildfire regime.