Flammability of native perennial grasses in temperate Australia as influenced by dryness, fire intensity and species

Background Grasses significantly influence bushfire behaviour in fire-prone landscapes, yet their contribution to flammability under changing climate and fire regimes in temperate Australia remains under-evaluated. Aims We examined the flammability of two native perennial grasses (P. labillardierei, T. triandra) across two fire intensities (low and high), and two dryness levels (well-watered and dry) under controlled laboratory conditions. Methods Plants were drought-treated for 5 weeks and burned to quantitatively assess four flammability components: ignitability, combustibility, sustainability and consumability. Key results Dryness significantly influenced all flammability components (P < 0.001) across fire intensities and species, except for flame duration (P > 0.05). High versus low fire intensity significantly increased all flammability components (P < 0.001), except ignition probability and time to flaming ignition. P. labillardierei was consistently more flammable than T. triandra for all components (P < 0.001). There were two-way interactive effects on flame height and biomass consumption, with stronger effects of dryness and fire intensity for P. labillardierei than T. triandra, and of fire intensity for well-watered than dry grasses (P < 0.001). Implications These findings suggest that increased fuel dryness and high fire intensity elevate the flammability of widespread native perennial grasses, increasing the risk of fire spread under drier future climates.