Lily Dun, Western Sydney University in New South Wales, Australia, and The University of Queensland in Queensland, Australia, discusses her article: Do trait-growth relationships vary with plant age in fire-prone heathland shrubs?
When we think about plant growth, we often assume that certain functional traits—such as wood density, leaf structure, or biomass allocation—determine how fast a plant grows, regardless of its age. This assumption is based on the idea that traits capture fundamental trade-offs in plant function, such as the classic growth-survival trade-off where fast-growing species invest less in structural support. For example, species with low wood density are often expected to grow faster because they allocate fewer resources to structural reinforcement. However, our research challenges this assumption. By studying 14 shrub species in fire-prone heathlands in eastern Australia, we found that relationships between traits and growth rates shift as plants mature. Understanding how these relationships change over time is critical for predicting plant ecological strategies—i.e. how species allocate resources, compete, and persist in their environments.
We measured growth at six different plant ages, from 1.4 to 32 years old, as determined by time since the last fire. Ages were identifiable from local fire history because all species regenerate from seed post-fire. We examined how functional traits—such as wood density, leaf mass per area, total leaf mass relative to wood mass, and nutrient content—related to growth rates. To capture the full breadth of plant growth strategies, we used five different metrics: stem diameter, height, total leaf area, and biomass both with and without turnover
Key Findings
Our results highlight three main insights:
- Age-dependent trait relationships: Trait-growth relationships were weakest in the youngest plants (1.4–2.4 years old), indicating that early growth may be more influenced by environmental variability than by inherent trait differences among species. As plants aged, these relationships became stronger, reinforcing the idea that functional traits play an increasingly important role over time.
- Most influential traits: We found that wood density and leaf mass fraction (the proportion of total aboveground biomass allocated to leaves) had the strongest effect on growth rate differences between species.
- Consistency across growth metrics: Despite differences in what each growth metric captures, the relationships between growth and traits were broadly consistent. This means that while different measures of growth provide complementary insights, they largely reflect the same underlying trait-driven growth strategies.
Why Does This Matter?
For ecologists, this study highlights the importance of considering ontogeny—how traits interact with growth at different life stages—rather than assuming a one-size-fits-all relationship. Incorporating these dynamic trait-growth relationships into ecological models can improve our ability to predict plant community dynamics. This is particularly important in fire-prone ecosystems, where understanding species’ growth strategies informs conservation efforts and ecosystem management.
