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Proteas as ‘tumbleseeds’: Wind dispersal through the air and over soil

W. Bond

Published 1988 in South African Journal of Botany

ABSTRACT

The fruits of the genus Protea have long stiff trichomes forming a pappus-like structure. In serotinous species the achenes (seeds) are released only after fire when vegetative barriers to dispersal are minimized. The dispersal of seed by free-fall from the cones to the ground (phase I) was compared with subsequent dispersal by rolling over the substrate (phase II). Seed shadows observed in the field as well as seed release under controlled conditions suggest that phase I dispersal is seldom more than 30 m. However phase II dispersal distances measured both from seed shadows and controlled-release experiments were much greater, frequently exceeding 50 m with a maximum over 500 m. The most important biological determinant of both phase I and phase II dispersal was the size of the tuft of hairs and wing loading of the seed. Substrate roughness was a major physical determinant of phase II dispersal distance. In rocky areas, phase II dispersal can be effectively discounted. In smooth areas, previous estimates of Protea migration rates may be an order of magnitude too low. Other Cape Proteaceae with hairy seeds and serotinous cones occur in Aulax and a few species of Leucadendron. This convergence suggests that long-distance phase II transport may have adaptive value.

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