Examining forest resilience to changing fire frequency in a fire‐prone region of boreal forest

• Published in: Global change biology 2019-03, Vol.25 (3), p.869-884
• Main Authors: Hart, Sarah J., Henkelman, Jonathan, McLoughlin, Philip D., Nielsen, Scott E., Truchon‐Savard, Alexandre, Johnstone, Jill F.
• Format: Article
• Language: English
• Subjects: Age; Age composition; alternative stable state; black spruce; Boreal forests; Climate change; Composition; Computer simulation; Coniferous forests; Data; Deciduous trees; Ecological effects; Ecological monitoring; Ecological succession; Fires; Forest fires; Forests; Geographical information systems; Hypotheses; immaturity risk; Interactions; jack pine; Landscape; Modelling; Negative feedback; Probability theory; Resilience; resistance; self‐regulation; Simulation; spatially explicit state‐and‐transition simulation model; Switches; Taiga; Vegetation; Wildfires
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.14550

Future changes in climate are widely anticipated to increase fire frequency, particularly in boreal forests where extreme warming is expected to occur. Feedbacks between vegetation and fire may modify the direct effects of warming on fire activity and shape ecological responses to changing fire frequency. We investigate these interactions using extensive field data from the Boreal Shield of Saskatchewan, Canada, a region where >40% of the forest has burned in the past 30 years. We use geospatial and field data to assess the resistance and resilience of eight common vegetation states to frequent fire by quantifying the occurrence of short‐interval fires and their effect on recovery to a similar vegetation state. These empirical relationships are combined with data from published literature to parameterize a spatially explicit, state‐and‐transition simulation model of fire and forest succession. We use this model to ask if and how: (a) feedbacks between vegetation and wildfire may modify fire activity on the landscape, and (b) more frequent fire may affect landscape forest composition and age structure. Both field and GIS data suggest the probability of fire is low in the initial decades after fire, supporting the hypothesis that fuel accumulation may exert a negative feedback on fire frequency. Field observations of pre‐ and postfire composition indicate that switches in forest state are more likely in conifer stands that burn at a young age, supporting the hypothesis that resilience is lower in immature stands. Stands dominated by deciduous trees or jack pine were generally resilient to fire, while mixed conifer and well‐drained spruce forests were less resilient. However, simulation modeling suggests increased fire activity may result in large changes in forest age structure and composition, despite the feedbacks between vegetation–fire likely to occur with increased fire activity. Here, we study fire and forest dynamics in Saskatchewan's Boreal Shield to better understand the resilience and resistance of North American boreal forests to projected increases in fire activity. Both field and GIS data show evidence for self‐regulation of fire, where young, recently burned forest stands are more resistant to fire than older stands, and immaturity risk, where short‐interval fires reduce forest resilience to fire. However, simulation modeling suggests increased fire activity may result in large changes in forest age structure and composition, despite the feedba