Testing key tenets of pyro-ecophysiology: Indicators of drought response in relation to shoot flammability

Abstract

Premise: Relationships between flammability and drought tolerance influence vegetation dynamics during fires. A goal of the emerging subdiscipline of pyro-ecophysiology is to identify ecophysiological traits that determine live fuel flammability, but empirical studies of these relationships are rare. Furthermore, drought tolerance has been suggested as a surrogate for low flammability when choosing species to plant near houses in fire-prone areas, but this hypothesis has not been tested. Methods: We examined links between flammability and drought tolerance for 39 woody species, compiling existing data on shoot flammability and six drought-related variables: minimum leaf water potential (Ψmin; N = 15 species), leaf turgor loss point (πtlp; N = 20), root zone water deficits (N = 19), days to plant death (N = 14), xylem embolism resistance (P₅₀; N = 20), and wood density (WD; N = 20). Results: Drought-tolerant species did not have low shoot flammability, except for a negative relationship between ignition percentage and WD, and then only for conifers. In contrast, there were significant negative relationships between four of five shoot flammability variables and either or both Ψinf and πtlp, showing that the most drought-tolerant species were also the most flammable. Ψmin and πtlp were positively associated with leaf water status, producing higher correlations with shoot flammability than other drought-response indicators. Conclusions: Pyro-ecophysiological traits, e.g. Ψmin and πtlp, are useful predictors of interspecific variation in live fuel flammability, showing how pyro-ecophysiology can provide insights into how plants might respond to a more drought- and fire-prone future.