Implications of terminal velocity and wing loading Hakea (proteaceae) seed dispersal

Abstract

Hakea (Proteaceae) has winged seeds that rely on wind movement for dispersal, with seed dispersal being most effective in a post-fire environment. Seeds from 14 southwestern Australian species (8 fire-killed, 6 resprouters) had their seed mass, wing loading, and terminal falling velocity recorded to determine if a) overall relationships existed between seed properties and seed aerodynamics, and b) if seed dispersal was inherently different between the two post-fire persistence strategies. An increase in seed wing loading, calculated as the mass divided by area of the winged seed, resulted in an increase in seed terminal velocity. Using terminal velocity data to estimated initial seed dispersal distance, Hakea seeds have the potential to be dispersed up to 5 m from a parent plant, assuming seeds dispersed from less than 1.5 m above ground, and prevailing wind speeds of no more than 5 m s -1. However, under field conditions Hakea seeds are dispersed up to 20 m from the nearest adult. Secondary dispersal, the movement of seeds across the ground, is therefore more important in explaining Hakea post-fire dispersal patterns, and is a function of seed mass, prevailing surface wind conditions and the occurrence of litter microsites. Despite detecting no significant difference in wing loading or terminal velocity between fire-killed and resprouting in this study, field observations suggest that seeds of resprouter Hakea species tend to disperse their seeds further away from the parent plants.