Abstract
The distribution of wind-dispersed seeds around a parent tree depends on diaspore and tree traits, as well as wind conditions and surrounding vegetation. This study of a neotropical canopy tree, Platypodium elegans, explored the extent to which parental variation in diaspore and tree traits explained (1) rate of diaspore descent in still air, (2) distributions of diaspores dispersed from a 40-m tower in the forest, and (3) natural diaspore distributions around the parent tree. The geometric mean rate of descent in still air among 20 parents was highly correlated with geometric mean wing loading(1/2) (r=0.84). However, diaspore traits and rate of descent predicted less variation in dispersal distance from the tower, although descent rate(-1) consistently correlated with dispersal distance. Measured seed shadows, particularly their distribution edges, differed significantly among six parents (DBH range 62-181cm) and were best fit by six separate anisotropic dispersal kernels and surveyed fecundities. Measured rate of descent and tree traits, combined in a mechanistic seed dispersal model, did not significantly explain variation among parents in natural seed dispersal distances, perhaps due to the limited power to detect effects with only six trees. Seedling and sapling distributions were at a greater mean distance from the parents than seed distributions; saplings were heavily concentrated at far distances. Variation among parents in the distribution tails so critical for recruitment could not be explained by measured diaspore or tree traits with this sample size, and may be determined more by wind patterns and the timing of abscission in relation to wind conditions. Studies of wind dispersal need to devote greater field efforts at recording the "rare" dispersal events that contribute to far dispersal distances, following their consequences, and in understanding the mechanisms that generate them.
Highlights
Distance and direction of dispersal affect a seed’s fate
Intraspecific variation in seed shadows and associated variation in parent fitness of a wind-dispersed species depend on diaspore traits such as wing loading, tree traits such as tree height and crown area, as well as wind conditions and surrounding vegetation that modify local winds
Few studies have investigated intraspecific variation in seed shadows resulting from wind dispersal, the factors explaining that variation (Nathan et al 2001; Norghauer et al 2011), or its consequences for recruitment (Schupp and Fuentes 1995; Nathan and Muller-Landau 2000)
Summary
Parent fitness depends on the distribution of seed trajectories, that is, on the full seed shadow. Not all environments within a seed shadow are important. Distance- and density-dependent mortality makes the tails important. Intraspecific variation in seed shadows and associated variation in parent fitness of a wind-dispersed species depend on diaspore traits such as wing loading, tree traits such as tree height and crown area, as well as wind conditions and surrounding vegetation that modify local winds. Few studies have investigated intraspecific variation in seed shadows resulting from wind dispersal, the factors explaining that variation (Nathan et al 2001; Norghauer et al 2011), or its consequences for recruitment (Schupp and Fuentes 1995; Nathan and Muller-Landau 2000).
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