Modelling Variable Fire Severity in Boreal Forests: Effects of Fire Intensity and Stand Structure

Area of Science:

• Forest Ecology
• Fire Science
• Remote Sensing

Background:

• Boreal forest fires exhibit significant variation in severity, impacting tree mortality within and across individual fire events.
• Understanding the factors driving this variability is crucial for effective forest management and ecological understanding.

Purpose of the Study:

• To investigate the influence of fire intensity, stand structure, species composition, and geographic region on fire severity in boreal forests.
• To develop and utilize a model simulating fire severity based on empirical relationships and stand characteristics.

Main Methods:

• Integrated forest plot data, tree allometries, and historical fire records into a diameter class-structured model for black spruce and jack pine stands.
• Simulated crown fire initiation, vertical spread, and used empirical relations to model fire intensity, scorch height, and tree mortality.
• Employed random forest and regression tree analyses to assess the impact of various factors on simulated fire severity.

Main Results:

• Fire severity increased with fire intensity and was lower in jack pine stands compared to black spruce stands.
• High-severity fires (>75% basal area reduction) occurred in 80% of simulated black spruce stands versus 11% of jack pine stands.
• Identified thresholds where stand structure significantly influenced fire severity, particularly in interaction with fire intensity.

Conclusions:

• Stand structure is a key factor contributing to the observed variation in boreal fire severity, alongside fire intensity.
• The developed model successfully reproduced fire severity variations under diverse fire intensity conditions.
• Pyrogeographic region did not show a residual effect on simulated severity after accounting for stand structure and species composition.