Fire regimes of southern Alberta, Canada

• Author / Creator

  Rogeau, Marie-Pierre

• After decades of recent fire exclusion in southern Alberta, Canada, forests are progressively aging and landscape mosaics are departing from their historical conditions. A large-scale fire history study spanning three natural subregions: Subalpine, Montane and Upper Foothills, was undertaken to understand fire return intervals (FRI) prior to the period of effective fire suppression (pre-1948). This thesis presents an approach to conducting field-based fire history studies in remote landscapes. A paired-plot sampling approach was used to deal with landscapes regulated by large-scale, fully lethal, and mixed severity fires, where fire scar evidence is lost over time. For each natural subregion, point FRIs were used to conduct a fire frequency (i.e. survival) analysis that considers both FRI and time-since-fire data. A total of 3123 tree samples were collected at 814 sampling sites, from which 583 fire scars were identified. Results showed natural subregions had different fire interval distributions before 1948 and some level of FRI variance was also observed within a subregion. The median FRI for the Montane and Foothills sampling units ranged from 26 to 39 years, while the sampling unit located in the most rugged portion of the Subalpine had a median FRI of 85 years. Other aspects of the fire regime were also documented for the three natural subregions including: severity, seasonality and cause. These results revealed an important anthropogenic influence on the amount and spatial distribution of burning prior to 1948. In contrast, the effective fire suppression measures taken since 1948 resulted in a substantial departure of 167% to 223% (median FRI = 84 to-104 years) for the Montane and Foothills, while the rugged Subalpine was found to be within its natural range of variation with a departure of 42% (median FRI = 121 years). These findings may have important impacts for how wildland fire and forest management guidelines are set today, and in the future. Another objective of this research was to evaluate the effects of topography on wildfire distribution. The aim of this study was to quantify the effects of elevation, aspect, slope and dominant species on probability of burning, and to re-evaluate the same effect when the forest is partitioned by seral stages. Fire return interval data were stratified by subregion and analyzed with the non-parametric Kaplan-Meier survival model and Cox Proportional Hazards regression model for survival data. The natural subregions were found to have distinct fire distributions with elevation and aspect being significant variables affecting the probability of burning. However, this effect was not constant across all seral stages. The outcome of this study contributes to understanding the ecological role of fire in mountain landscapes and where fire-adapted plant communities prevail. The impact of topography on fire frequency is variable with seral stage and is pertinent to forest and fire management activities such as ecological restoration needs, protection of old growth forests, and distribution of harvest blocks that are intended to spatially emulate natural disturbances.

• Subjects / Keywords

  • Fire regime
  • Fire return interval
  • Montane
  • Canadian Rockies
  • Fire history
  • Foothills
  • Subalpine
  • Effect of topography

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3CV4C309

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.