Assessing the effect of tissue and fire‐response traits on plant growth rates post‐disturbance in eastern Australia

Variation in plant growth strategies facilitate species' coexistence in a community. Some functional traits are predicted to influence the growth rates of developing individuals by capturing trade‐offs in resource allocation. However, despite being used broadly in community ecology, the assumed generality and predictability of trait‐growth relationships lack widespread empirical testing.

The megafires of 2019–2020 burned extensive areas throughout New South Wales and were followed by high rainfall, causing the large‐scale synchronous regeneration of fire‐adapted species. We took advantage of this mass disturbance event to test hypothesised relationships between functional traits and growth across six spatially distributed sclerophyllous systems throughout NSW, in which sampled vegetation was part of the same growth cohort.

We investigated whether resprouting as a trait facilitated faster initial height growth compared to reseeding and, in reseeding species, tested whether the effects of four structural functional traits—stem specific density (SSD), leaf nitrogen per area, standardised stem diameter and specific leaf area (SLA)—on height growth rates followed directions predicted by theory.

Resprouters grew an average of 25.92 cm year⁻¹ more than reseeders at 14–15 months post‐fire, indicating an advantage in light capture over reseeding species in the period soon after fire. Of the four structural functional traits tested, SSD and leaf nitrogen per area displayed evidence of relationships with height growth rate, while standardised stem diameter and SLA had no evidence of an effect. These relationships were consistent across sites.

Our results indicate that (i) ontogenetic variation in growth rates should be integrated into the fast‐slow growth economics spectrum and that (ii) while some functional traits predict height growth, this is not a guarantee for all traits.