Abstract
Widespread fire exclusion and land-use activities across many southeastern United States forested ecosystems have resulted in altered species composition and structure. These changes in composition and structure have been implicated in positive fire-vegetation feedbacks termed “mesophication” where fire spread and intensity are diminished. In forests and woodlands, inherent flammability of different species is the mechanistic driver of mesophication. To date, there has been limited work on documenting the high diversity of flammability among species in the region, limiting the ability to differentiate among species to restore fuels that sustain fire regimes. Here, we coalesce disparate flammability data and add missing species across the spectrum from species that facilitate fire (so called “pyrophytes”) to those that dampen fire (so called “mesophytes”). We present data on 50 important tree species from across the southeast, all burned using identical laboratory methods. We divide our results for four dominant ecosystems: Coastal Plain uplands, oak-hickory woodlands, Appalachian forests, and bottomland forests. Across ecosystems, the most flammable species were American chestnut (Castanea dentata), a suite of pines (Pinus palustris, P. elliottii, P. serotina, and P. rigida), several oaks (Q. laevis, Q. falcata, Q. margaretta, and Q. alba), and sourwood (Oxydendrum arboreum). At the mesophytic end, the least flammable species were Tsuga canadensis, Acer rubrum, and several other hardwoods previously implicated in mesophication. Each of the four ecosystems we studied contained species that spanned the pyrophytic to mesophytic gradient. These data fill in some key holes in our understanding of southeastern fire adaptations, but also provide context for restoration decisions and fire management prioritization efforts to restore and sustain fire-prone ecosystems of the region.
Highlights
Widespread fire exclusion and land-use change have resulted in dramatic impacts on species composition, structure, and ecological processes of many fire-prone terrestrial ecosystems
The classic mesophytes Acer rubrum, Tilia americana, Liquidambar styraciflua, and Nyssa sylvatica tended to burn with low flammability
Many of the species implicated in mesophication (e.g., A. rubrum, Tilia americana, Liquidambar styraciflua, and Nyssa sylvatica; Nowacki and Abrams, 2008; Kreye et al, 2018b; Babl et al, 2020) had lower flammability that diminishes fire intensity and spread, enabling these species to persist in the presence of low intensity fires or continued fire exclusion
Summary
Widespread fire exclusion and land-use change have resulted in dramatic impacts on species composition, structure, and ecological processes of many fire-prone terrestrial ecosystems. The recruitment of firesensitive mesophytes coincided with increasing tree density, the formation of heavily shaded, multi-canopied forests, and development of moist forest floor conditions that resist ignition (Kreye et al, 2018a,b) This positive feedback phenomenon has been widely observed and is commonly referred to as “mesophication” (Nowacki and Abrams, 2008; Hanberry et al, 2020; Alexander et al, 2021). In spite of the clear evidence of frequent fire and numerous species that are enhanced by fire, substantial gaps remain in the understanding of firerelated traits across tree species in the region Protective traits such as thick bark and rapid wound closure allow fire-tolerant species to persist in fire-prone landscapes (Landers, 1991; Jackson et al, 1999; Romero et al, 2009; Varner et al, 2016). Field measurements in forests, woodlands, and savannas validate the relative importance of senesced litter as the primary mechanistic driver of surface fire behavior (Wenk et al, 2011; Whelan et al, 2021)
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