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

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.

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 (Ψ_min; N = 15 species), leaf turgor loss point (π_tlp; 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).

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 Ψ_min and π_tlp, showing that the most drought-tolerant species were also the most flammable. Ψ_min and π_tlp were positively associated with leaf water status, producing higher correlations with shoot flammability than other drought-response indicators.

Pyro-ecophysiological traits, e.g. Ψ_min and π_tlp, 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.