Wind dispersal is predicted by tree, not diaspore, traits in comparisons of Neotropical species

The seed shadow created by wind dispersal around parent trees may be affected by functional traits, as well as wind conditions and surrounding vegetation. This study of one mature tree each of 12 Neotropical species determined the extent to which species variation in diaspore traits vs. tree height and crop size explains (i) rate of diaspore descent in still air, (ii) distributions of diaspores dispersed from a 40-m tower in the forest, and (iii) natural seed shadows around the parent tree. A model of diaspore wing-loading to a fitted power explained 66·9% of the variation among species in the geometric mean rate of descent in still air. For a subset of four species, expected dispersal distance was not correlated with actual dispersal distance from the forest tower. For a subset of seven species, variation in wing-loading^0·5 of individual diaspores explained ≤4·3% of the dispersal distance from the parent tree. Measured seed shadows, particularly their distribution edges and area, differed significantly among the 12 species (range in maximum tree height 19–42 m) and were best fit by 12 separate anisotropic dispersal kernels and surveyed fecundities. Measured mean distance was highly correlated with simulated distances from the kernels. The best models, explaining 57·6% of the variation among species in shadow area, and 59·6, 61·6 and 61·7% of variation in mean, median and maximum distances, included maximum tree height, either alone or in combination with crop size, and not diaspore rate of descent. Among 10 species, seed shadow area was not related to rank of seedling shade tolerance. In their highly skewed distributions, most seeds were much closer than the distance of greatest seedling recruitment and in very high density, thus enhancing later density- and/or distance-related seedling mortality. Tree functional traits, rather than the historically emphasized diaspore traits, explain distance distributions of these wind-dispersed species. Additional exploration of diaspore abscission in relation to wind and the influence of wind patterns after release are needed. A lay summary is available for this article.