Fire and tree death: understanding and improving modeling of fire-induced tree mortality

Abstract

Each year wildland fires kill and injure trees on millions of forested hectares globally, affecting plant and animal biodiversity, carbon storage, hydrologic processes, and ecosystem services. The underlying mechanisms of fire-caused tree mortality remain poorly understood, however, limiting the ability to accurately predict mortality and develop robust modeling applications, especially under novel future climates. Virtually all post-fire tree mortality prediction systems are based on the same underlying empirical model described in Ryan and Reinhardt (1988 Can. J. For. Res. 18 1291-7), which was developed from a limited number of species, stretching model assumptions beyond intended limits. We review the current understanding of the mechanisms of fire-induced tree mortality, provide recommended standardized terminology, describe model applications and limitations, and conclude with key knowledge gaps and future directions for research. We suggest a two-pronged approach to future research: (1) continued improvements and evaluations of empirical models to quantify uncertainty and incorporate new regions and species and (2) acceleration of basic, physiological research on the proximate and ultimate causes of fire-induced tree mortality to incorporate processes of tree death into models. Advances in both empirical and process fire-induced tree modeling will allow creation of hybrid models that could advance understanding of how fire injures and kills trees, while improving prediction accuracy of fire-driven feedbacks on ecosystems and landscapes, particularly under novel future conditions.

Biogeography of fire regimes in western U.S. conifer forests: A trait‐based approach

“…Our FRS could also be refined with improved data on bark, via better vertical allometry and roughness across multiple species (Jackson, Adams, & Jackson, 1999) that provide a better indication of cambial exposure time to heat from fires. Additional work that quantifies differential sensitivity of species to crown scorch and other fire injuries could be added as those data are developed (Hood et al, 2018). Lastly, availability of both trait data and spatial data for the traits and species we considered was generally limited to the species level (and not to widespread subspecies, as in the diverse Pinus ponderosa , Pinus contorta and Pseudotsuga menziesii ); therefore, we did not consider potentially important subspecies‐level biogeographical variation that could be incorporated into future work.…”

Frequent fire reorganizes fungal communities and slows decomposition across a heterogeneous pine savanna landscape

“…In many of these 'pyrogenic' systems, dominance of flammable grasses in the ground layer promotes the spread of fire (Beckage et al, 2011;Staver et al, 2011;Cardoso et al, 2018), which prevents ecosystem transition to a different state (Beckage et al, 2009;Callaham et al, 2012;Dantas et al, 2016;Pausas & Bond, 2019). Unlike high-profile, destructive wildfires (Chen, 2006;Hood et al, 2018), frequent low-intensity fires are essential for maintaining biotic and abiotic components of 'pyrogenic' biomes (Fill et al, 2015;He & Lamont, 2018) that include some of the most diverse plant communities on Earth (Bond et al, 2005;Noss et al, 2015;Peet et al, 2018). Frequent prescribed burning is currently used to mimic natural fire regimes and help conserve many pyrogenic ecosystems and their biodiversity (Peet et al, 2018).…”

Resilience of Oregon white oak to reintroduction of fire

“…Not all fire effects contributed equally to dieback in oak crowns. Charring at DBH was a contributor to our final model, but as neither of the other bark char variables was significant, char height may simply be an indicator of substantial heat reaching the crown, and not a sign of underlying cambial damage (Hood et al 2018). Trees with greater quantities of crown scorch were more likely to experience dieback the following spring, while tree size was a mitigating factor in the model.…”

“…Previous studies have found that extensive crown scorch can cause mortality in a variety of conifer species (Hood et al 2018), as well as result in topkill among some oak species (Babb 1992), but this relationship has not been well examined for Oregon white oak. Longduration smoldering of accumulated basal duff can also injure or kill trees via cambial injury or harm to fine roots in long-unburned sites (Swezy and Agee 1991;Miyanishi and Johnson 2002;Stephens and Finney 2002;Varner et al 2005;Varner et al 2009).…”