Post-fire vegetation regeneration during abnormally dry years following severe montane fire: Southern Alberta, Canada

Abstract

Fire regimes across montane regions of western Canada are changing resulting in longer fire seasons, higher intensity fires, and shortening fire return intervals. The implications of high severity fire and warmer, drier early post-fire conditions on herbaceous understory vegetation regeneration and seedling recruitment in the southern Canadian Rockies are not well known. The overall objective of this study is to quantify trajectories of vegetation recovery (species, structural characteristics, and biomass) during early years of abnormally warm, dry conditions following a high severity fire in two moisture endmember sites Waterton Lakes National Park, Alberta, Canada. Here, we compare the within and between year spatial and temporal variability of vegetation growth and species density and how these change over time and across the broader area as an indicator of ecosystem resilience within these endmember sites. Moderate to extreme drought occurred during the years following fire at Waterton, where 2021 was ranked as the 2nd driest year in 26 years. Despite this, the moist site was characterised by greater herbaceous vegetation recovery with few lodgepole pine seedlings (average biomass = 335 g m⁻²), while a drier site had greater seedling recruitment over a period of 5 years. Variations in site environmental conditions were more impactful than differences between years (drought) on post-fire vegetation recovery. Use of remotely piloted aircraft system (RPAS) remotely sensed data provided an effective means for quantifying variability in regenerating vegetation height (structure from motion), cover (green chromatic coordinate), and biomass when compared at plot level (R² = 0.53, 0.53, and 0.30 respectively) using optical photogrammetric methods. The research presented has implications for forest and fuel management in Canada as national parks and forest agencies consider historic use of heterogeneous species patches. High density of lodgepole pine seedling recruitment in mineral soils and under very dry conditions indicate resilience to drought. This will require continued and expanded monitoring as other tree species recruits populate the post-fire environment.