Does pyrogenicity protect burning plants?

Abstract

Abstract. Pyrogenic plants dominate many fire-prone ecosystems. Their prevalence suggests some advantage to their enhanced flammability, but researchers have had difficulty tying pyrogenicity to individual-level advantages. Based on our review, we propose that enhanced flammability in fire-prone ecosystems should protect the belowground organs and nearby propagules of certain individual plants during fires. We base this hypothesis on five points: (1) organs and propagules by which many fire-adapted plants survive fires are vulnerable to elevated soil temperatures during fires; (2) the degree to which burning plant fuels heat the soil depends mainly on residence times of fires and on fuel location relative to the soil; (3) fires and fire effects are locally heterogeneous, meaning that individual plants can affect local soil heating via their fuels; (4) how a plant burns can thus affect its fitness; and (5) in many cases, natural selection in fire-prone habitats should therefore favor plants that burn rapidly and retain fuels off the ground. We predict an advantage of enhanced flammability for plants whose fuels influence local fire characteristics and whose regenerative tissues or propagules are affected by local variation in fires. Our ''pyrogenicity as protection'' hypothesis has the potential to apply to a range of life histories. We discuss implications for ecological and evolutionary theory and suggest considerations for testing the hypothesis.

The reproductive response of an endemic bunchgrass indicates historical timing of a keystone process

“…In the LLPE, the fire phenology is a key influence on the timing of flowering in wiregrass and other pine savanna v www.esajournals.org dominants (Platt et al 1991, Shepherd et al 2011. Therefore it is possible that these species have evolved mechanisms by which to reinforce the continued predictability of fire (Gagnon et al 2010, Keeley et al 2011. For instance, wiregrass experiences year-round root production, with much greater root growth occurring during the winter relative to Schizachyrium scoparium (little bluestem), which experiences root growth primarily during the growing season (West 2002).…”

“…Perhaps this root proliferation in wiregrass represents not only nutrient uptake as suggested by West (2002), but also a ''shunting'' of nutrients from the leaves to belowground structures prior to the times that summer fires were most likely to occur. This would not only contribute to the survival and growth of wiregrass post-fire, but it would also make the leaves more flammable during the fire season (Gagnon et al 2010).…”

Have plants evolved to self-immolate?

“…A number of theoretical models have attempted to reconcile the evolution of flammability with individualistic selection theory by proposing ways that self-immolation can increase individual fitness or advantage to their offspring (Bond and Midgley, 1995; Kerr et al, 1999; Gagnon et al, 2010). For instance, Bond and Midgley (1995) developed a “kill thy neighbor” model, which demonstrated that a trait promoting canopy flammability amongst a population of closely spaced conspecific individuals could increase reproductive fitness on the condition it also conferred other evolutionary advantages.…”

“…Recently, Midgley (2013) has withdrawn his support for this model because of unrealistic assumptions, such as the need for the seed shadow of the flammable individual to closely align with the fire footprint, and for its seedlings that inherit the flammable trait to be more competitive in post-fire environments. Likewise, Midgley (2013) argues that the “pyrogenicity as protection” hypothesis (Gagnon et al, 2010), which posits that flammable crowns are protective of soil seed banks and subterranean bud banks, shares similar flaws to the Bond and Midgley (1995) model.…”

Altered Community Flammability in Florida’s Apalachicola Ravines and Implications for the Persistence of the Endangered Conifer Torreya taxifolia

“…Flammability of senesced leaves, cones, or sloughed bark [2]–[4] can facilitate the spread and intensity of fires in some plant communities and impede or dampen fire in others [5]–[7]. Flammability has been quantified as a combination of ignitibility of fuel (energy required for combustion), combustibility (intensity, flame height, energy output), sustainability (duration of flaming and smoldering), and consumability [mass loss; 8].…”