Department of Parks adn Wildlife
Many plants are able to convert atmospheric nitrogen to organic nitrogen
Many plants are able to convert atmospheric
nitrogen to organic nitrogen. Photo © Parks and Wildlife

Fire, plants and vegetation

Fire is an ecologically friendly and cost effective tool to regenerate and rehabilitate vegetation on disturbed sites. It helps new seedlings by temporarily reducing competition from established vegetation and creating ash beds suitable for germination. Fire is used:

Fire fact

Eucalypts and some members of the Proteaceae family such as some banksia species have a swelling at the base of the stem just below the soil that contains dormant buds, which burst into life when the top growth is killed by fire. This is known as a lignotuber.

Fire and grasslands

Applying fire early in the dry season to annual sorghum grasslands kills the sorghum before viable seed is set. This decreases the amount of annual sorghum in the next two or three years in favour of other perennial grasses. Applying fire to grasslands when fire intensity is higher reduces the survival of shrub and tree species. But if fire is applied when fire intensity is low, it allows tree and shrub species to survive, favouring the development of a woodland structure. For further reading visit the Bushfire and Natural Hazards CRC.

Protective equipment checklist
The fire/nitrogen cycle
(Select image for larger view)

Australian plants have adapted to persist in a fire prone environment along with regular droughts and the nutrient poor soils that are a feature of our environment.

Most plants can re-shoot from protected buds on their stems or roots, so they can recover rapidly after a fire. Thick bark protects these buds from the damaging heat of fires.

Many plants hold their seeds in thick woody fruits or capsules, where they are protected from fire. The heat of the fire assists in opening the capsules, allowing the seeds to be shed within a few days. When the seeds fall to the ground they land in the ash bed, which is high in the nutrients needed for strong seedling growth.

Nitrogen is in short supply in most Australian soils, but is vital for plant growth as it is required for amino acids, which are the basic building blocks of cells. When a fire burns a plant, most of the nitrogen within the plant is lost to the atmosphere. This is compensated for by the fire-stimulated regeneration of legumes and other plants that can fix nitrogen from the atmosphere.

Bacteria in the root nodules of the plants are able to convert nitrogen from the atmosphere into a form that can be used by plants. Many of the first plants that appear after a fire, such as wattles (acacias) and pea-flowering plants which are often called 'fire weeds', have this nitrogen converting ability, and are able to rapidly rebuild the nitrogen supplies in the soil that are subsequently available to all the plants at the site.

Parks and Wildlife has done extensive plant conservation research on this topic.