Continental-scale empirical evidence for relationships between fire response strategies and fire frequency

Theory suggests that the dominance of resprouting and seeding, two key mechanisms through which plants persist with recurrent fire, both depend on other traits and vary with fire regime. However, these patterns remain largely untested over broad scales. We analysed the relationships between mean fire frequency, derived from MODIS satellite data, and resprouting and seeding strategies, respectively, for c. 10 000 woody and herbaceous species in Australia. We tested whether leaf economics traits differed among these strategies. Probability of resprouting exhibits a monotonic increase with fire frequency for woody plants; for herbaceous plants, a hump-shaped relationship is observed. Probability of seeding exhibits a hump shape with fire frequency in woody plants. In herbaceous plants, probability of resprouting was associated with higher leaf mass per area (LMA), and probability of seeding with lower LMA. A broader range of leaf investment strategies occurred in woody plants. Our findings provide the largest empirical support to date for theory connecting fire response strategy to fire frequency. Woody seeders appear constrained by immaturity and senescence risk. Herbaceous and woody seeders showed different placements along the leaf economics spectrum, suggesting an important interaction between growth form and growth rate for seeders.