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:

  • to stimulate the release of seed from capsules held in the crowns of forest trees after timber harvesting
  • to prepare the seed bed by providing ash that is full of beneficial nutrients such as potash
  • in the arid zone, to assist rehabilitation after mineral exploration or grazing
  • to favour the development of either grasslands or woodlands by applying fire in particular seasons and frequencies
  • to manage weeds, some of which, such as rubber vine (Cryptostegia madagascariensis), giant sensitive plant (Mimosa pigra) and prickly acacia (Acacia nilotica), were once treated with herbicides, biocontrol agents or mechanical treatments
  • to manage vegetation structure and composition so there is always suitable habitat available in the landscape, like healthy thickets of melaleucas and poison peas (Gastrolobium) in the south-west forests.

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.

  • The rubber vine is a weed that is controlled through herbicides and fire. Photo © Julie Cox
  • Lush green shoots seen on the branches and stems of trees following a fire are called epicormic shoots. Photo © Parks and Wildlife
  • The scarlet banksia (Banksia coccinea) is one of the many plants that have adapted to fire by producing large woody fruits. Photo © Parks and Wildlife

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.