Seeds and fire
​How do Aussie plants ensure they have seeds ready to germinate after a fire?
Some species, including Banksias, Hakeas, Bottlebrushes (Callistemon species) and She-oaks (Casuarina species), store their seeds in woody cones or capsules. In fire-prone regions many of these species release their seeds only, or mostly, just after a fire. The technical word for this is “serotiny”. Once they are released, these seeds are ready to germinate. If this does not happen, they do not live long in the soil.
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1. Wallum Banksia (Banksia aemula), Bribie Island, Qld.
2. Conesticks (Petrophile pulchella), Kenthurst, NSW.
3. Needlebark Stringbark, (Eucalyptus planchoniana), Brisbane, Qld. Photo by Paul Donatiu.
Photos:
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1. A Banksia cone 6 weeks after fire. The protective pods have opened and the winged seeds have already blown away.
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2. Conesticks 6 months after fire. Some seeds are still coming out of the cone's compartments.
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3. This photo was taken a couple of days after a planned burn – these gum-nuts have fallen and opened, spilling out seeds.
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Storing up seeds in the soil is another strategy. Many species in fire-prone regions store seeds this way, often with some sort of dormancy mechanism so they won’t germinate until conditions are right.
Heat stimulates germination in many Australian species. This applies to most legumes – peas and wattles. Smoke also plays a role for many species, including some Grevilleas and the pink-flowered Kunzea capitata. For quite a few species, both heat and smoke cue germination.
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Some species with a soil seed-bank have additional germination requirements, such as exposure to particular temperatures.
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And of course, seedlings need good soil moisture before they will emerge.
Dusky Coral Pea (Kennedai rubicunda)
Purple Coral Pea (Hardenbergia violacea)
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Swamp Wattle (Acacia elongata)
Handsome Bush-pea (Pultenaea stipularis)
Species whose seeds respond to heat
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All four of these native legumes germinated best when their seeds were heated experimentally.
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Kunzea capitata
Grevillea seedling
Frey Spider Flower (Grevillea buxifolia)
Red Spider Flower (Grevillea speciosa)
Species whose seeds respond to smoke
Research has found that seeds of the three species pictured above respond to smoke. The two Grevilleas also respond to heat, but to a lesser extent. Smoke was the primary germination cue for the Kunzea. The photo of the seedling was taken in Ku-ring-gai Chase National Park, 8 months after fire.
A third strategy to ensure seeds are ready to take advantage of the post-fire environment, is to CREATE them soon after the fire. Read about rapid post-fire flowering here (coming soon).