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Fire
Natural fire regime in undisturbed areas of bushland is not a bad thing as most native plant species have evolved ways of surviving fire. In fact some native species actually depend on it for survival, as seeds will not germinate until after a fire eg Banksia and Acacias (wattles). However, in a natural situation, there can be a significant amount of time between fires. It is when fires occur less than five years apart that problems arise. Isolated pockets of bushland in the urban area are particularly susceptible to the effects of fire.
Native plant species have evolved a variety of tactics to survive fire. Some plants rely on:-
- excessive seed production
- germination of seeds only after they have been exposed to high temperatures of a fire. The woody fruit protects the seed from damage during the fire eg Hakeas
- underground storage organs from which regrowth can occur after a fire.
The woody fruit of Hakea plants protects the seed from damage by fire.
Eucalypts are extremely well adapted to fire and have evolved several tactics for survival. These include:
- Growth of new leaves from epicormic buds, found under the bark on the trunk of the plant. This allows them to immediately begin photosynthesising to supply the energy needed to stay alive and grow new leaves.
- Regrowth from lignotubers, woody storage organs at the base of the plant.
- Thick, corky bark to resist fire and protect the trunk
- Bark that hangs off the plant in strips. This encourages the spread of fire into the canopy, where the highly flammable eucalyptus leaves cause the fire to spread quickly and kill competitive species which may not be as well adapted to fire regime. This also ensures that the fire moves along faster, preventing damage from prolonged exposure to the heat
Leaves growing from epicormic buds on a Eucalypt after a fire.
Survival of the seedlings in after-fire conditions is often more likely as the conditions after a fire are ideal for seeds to germinate:-
- excess nutrients are available due to burn off of leaf litter
- sunlight penetration is increased
- fewer diseases as the soil has been partly sterilised
- fewer insects and other animals are present to eat the young plants
