Broadleaf tree phenology and springtime wildfire occurrence in boreal Canada

Area of Science:

• Ecology
• Forestry
• Remote Sensing

Background:

• Boreal forests, dominated by broadleaf species, have lower flammability than conifers.
• A critical period, the "spring window" (post-snowmelt, pre-greenup), presents elevated wildfire ignition and spread risks.

Purpose of the Study:

• To characterize the "spring window" duration, timing, and fire proneness across boreal Canada.
• To assess the relationship between these phenological variables and springtime wildfire incidence.

Main Methods:

• Utilized remotely sensed snow cover and greenup data (2001-2021) to define annual spring windows.
• Compared wildfire start seasonality (by cause) and fire-weather conditions.
• Employed path analysis to evaluate influences on wildfire number and seasonality.

Main Results:

• Spring window characteristics varied annually and geographically; western Canada exhibited the longest, most fire-conducive windows and highest wildfire activity.
• Springtime weather predominantly supported wind-driven, not drought-driven, wildfires.
• Wildfire seasonality was primarily driven by greenup timing, while wildfire numbers correlated with window duration and fire-conducive weather frequency.

Conclusions:

• The timing of greenup significantly influences the seasonality of boreal wildfires.
• Spring wildfire incidence is closely linked to the duration of the fire-prone "spring window" and conducive weather patterns.
• Findings aid in anticipating biome-wide changes and wildfire risks in North American northern forests.