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Keywords:

  • alpha and beta scales;
  • community assembly;
  • functional traits;
  • height;
  • leaf size;
  • seed size;
  • subtropical rain forest;
  • trait correlation structures;
  • trait-gradient analysis;
  • wood density

Summary

1. Plant functional traits are dimensions of ecological strategy variation and provide insights into the assembly of plant communities. For woody rain forest vegetation of northern coastal New South Wales, Australia, we quantified four continuous traits (leaf size, seed size, wood density and maximum height) for 231 freestanding woody species and documented community composition for 216 plots. Using trait-gradient analysis, we partitioned species trait values between alpha (within-site) and beta (among-site) components. This allowed us to identify both trait shifts along gradients and variation among co-occurring species.

2. Alpha trait components consistently varied more widely than beta components, meaning that trait variation among species within plots was wider than variation in the mean trait values of plots where species typically grow.

3. Beta trait components covaried significantly among leaf area, seed size, wood density and maximum height. For example, species found in habitats with a large mean leaf size were consistently also found in plots with large mean seed size (r = 0.70). Beta correlations show that these leaf, wood and seed traits respond in parallel to the dominant abiotic gradients: soil types, topographic position, elevation and large-patch disturbances such as those caused by cyclones–storms, landslips or fires.

4. In contrast, the alpha components of traits were largely uncorrelated among species. Alpha leaf area was not associated with alpha larger seeds, meaning that leaf area and seed size act as independent axes of differentiation among coexisting species.

5.Synthesis. The different correlation structures for alpha and beta components of traits reflect community assembly processes at different scales. Within sites, assembly processes have not created strong linkages among these traits. But across different sites in the landscape, abiotic drivers have created strong linkages.