Within the Proteaceae, 353 species confined to 7 genera in the Grevilleoideae
have woody fruits. The majority (> 70%) occur in fire-prone
vegetation on nutrient-poor, summer-dry soils of south-western Australia.
These species are characterised by large, winged seeds contained within
serotinous follicles. Seed release is mediated by desiccation of the follicle
walls resulting from fruit death, although wet–dry cycles are required
in some genera. After release, germination must take place by the next wet
season, as the seeds are not long-lived. Seeds are particularly high in
protein (40–60%), P (1–2%) and Fe
(10–60‰) compared with other Proteaceae. Seeds are favoured food
for pre- and post-dispersal granivores (insects, birds, rodents) and young
seedlings are favoured by herbivores (insects, marsupials), with the more
serotinous fruits providing extra protection for their seeds. Successful
establishment is facilitated by the protective and water retentive role of the
testa during germination, and the remobilisation of N and P from the
cotyledons to the seedling within 10 weeks of emergence. Drought stress
reduces seedling establishment in otherwise favourable postfire microsites and
prevents it (assisted by herbivores) in mature vegetation. Typically, <
10% of seeds released after fire become seedlings, and < 50%
of these survive the first summer. Among fire-killed species, species that
produce few seeds are more likely to have drought-resistant seedlings, often
associated with larger seeds and/or needle-shaped leaves. Species that
resprout after fire produce a few large viable seeds per plant, whereas
fire-killed species produce many smaller seeds. Of all the Proteaceae, the
ecology of woody-fruited species is best known, providing great scope for
comparative biology studies.
Seed Treatments for Disease Control