Fire intensity and pre-fire dryness shape the timing and degree of post-fire recovery in temperate native perennial grasses

Background Resprouting of native perennial grasses is central to their persistence and to fuel dynamics. Nonetheless, how changing environments influence resprouting success and vigor remains poorly understood for many perennial grass species. This is a significant knowledge gap in south-eastern Australia under predictions of drier and hotter climates and more frequent and severe fire weather. Methods We assessed the resprouting capacity of two widespread native perennial grasses, Poa labillardierei and Themeda triandra , under controlled glasshouse and laboratory conditions at two pre-burn dryness levels ('Well-watered', 'Dry') and two fire intensities ('Low', 'High'). We implemented dryness treatments for 5 weeks in a glasshouse before burning using a custom-built variable heat-flux apparatus, then assessed grass recovery for 10 weeks under well-watered conditions. Results Time to resprout was significantly delayed and relative growth rate (RGR), biomass recovery (%), and tiller number significantly increased by dry relative to well-watered pre-burn conditions. High fire intensity significantly delayed time to resprout and increased RGR, and species significantly influenced tiller number ( P. labillardierei > T. triandra ). Significant interactions between dryness and fire intensity were synergistic, such that time to resprout, RGR, and aboveground biomass recovery were greatest in the dry plus high-intensity treatment. Significant three-way interactions with species indicated the combined dryness-intensity effects were either more (time to resprout) or less (aboveground biomass recovery) pronounced for T. triandra than for P. labillardierei . Functional traits mediated interactive effects: high pre-burn leaf dry matter content was associated with delayed resprouting but enhanced subsequent growth, whereas higher specific leaf area promoted earlier resprouting and subsequent recovery. Conclusions Our study indicates that the individual and interactive effects of pre-fire dry conditions and high fire intensity can delay the onset of native perennial grass resprouting but will not necessarily compromise subsequent recovery trajectories provided water is available after a fire. The study also highlights the importance of considering pre-burn moisture conditions and species-specific recovery strategies in prescribed burning programs to minimize resprouting delays (and thus periods of soil exposure) and to predict post-burn fuel accumulation.