Alternative height strategies among 45 dicot rain forest species from tropical Queensland, Australia

1 Potential height, which spans at least an order of magnitude across species, is considered an important indicator of light capture strategy. Still, it remains unclear how potential height is coordinated with other traits that influence height growth rate, stem persistence and performance in low light. We proposed that contrasting correlations between potential height and other plant attributes would be observed for sets of species selected to span two hypothetical axes of light availability within mature forest and time since disturbance. 2 We selected 45 perennial rain forest species in Australia's wet tropics to span gradients of light availability and successional status and measured potential height together with traits influencing light capture and regeneration strategy on mature individuals. The traits included leaf mass per area, leaf nitrogen, wood density, stem mass per length, branch mass fraction and seed mass. 3 Potential height was significantly correlated with numerous traits among species selected to span each of the two gradients. Height was positively correlated with leaf mass area(-1), leaf nitrogen and seed mass and negatively correlated with leaf area ratio at the branch tip along both light and successional gradients. Height was positively correlated with wood density along the successional axis, with the opposite relationship along the light gradient. 4 Trait relationships differed in either slope or intercept between the two gradients, reflecting different strategic trade-offs. At a given height, shorter species in the successional gradient were characterized by lower leaf mass area(-1), lighter wood, smaller seeds, lower leaf nitrogen and lower leaf area ratio at the branch tip than similar sized species along the light gradient. 5 The results of this study support the idea of two distinct, trait-mediated axes of coexistence among short and tall plant species within vegetation. In several cases, trait relationships were weak or non-significant when species groupings were merged, indicating the importance of separating out the two sets for comparative studies.