Essay topic: Fire is a vital influence on Australia biotic patterns. Discuss the adaptations that allow Australian plants and animals to survive in periodically burned landscapes.
Fire plays a natural and often vital role in ecosystems across many parts of Australia. Some plants and animal communities are extremely sensitive to the destructive force of fire and within others it is not only tolerated but also often essential for maintaining biodiversity of species numbers. Fire helps to determine the types of flora and fauna found in an area and influences their evolutionary adaptations to survive the impacts of periodic fires. Research into the effects of fire on Australian biotic communities has provided much insight into the adaptive traits that allow both plants and animals to survive periodic fires. Major adaptations such as underground bud storage and aerial buds allow plants to survive and succeed in periodically burned landscapes, while animals utilise avoidance and other behavioural traits.
Upon germination of a seed, a plant does not move around within its ecosystem, as do animals. This makes them extremely susceptible to fire damage. Plants living in fire prone environments have therefore developed adaptive traits to allow their species to continue after fire has passed through the area. An adaptive trait in vegetation was summarised by Dobzhansky (1965 in Gill, Groves and Noble, 1981, p. 245) as 'an aspect of the developmental pattern which facilitates the survival and/or reproduction of its carrier in a certain succession of environments.'
If fires occur on a frequent basis, such as several times during a species' lifespan, then the plant needs to develop characteristics that allow it to survive the fire; at least until it reaches sexual maturity and can reproduce to ensure the species’ survival. If fire can only be expected once during the plants' lifetime, it is not important if the adult plant survives as long as it can reproduce in quantity immediately after the fire. An example of this type of survival trait is Allocasuarina stricta, which does not survive fire well yet regenerates afterwards in great numbers (Chandler, et al, 1991).
The survivability of plants can vary depending on the development stage reached at the time of the fire occurrence, as well as aspects such as fire severity and the time between fires (Gill et al, 1981). Therefore seedlings and herbaceous plants may be very sensitive whereas a mature plant may have much greater levels of damage tolerance in the way of bud protection through underground storage and/or in bark.
The insulative properties of soil and the characteristics of heat rising makes underground storage of buds a highly effective protective measure. Many plants show a number of methods for placing their buds out of harm. Lignotubers are one of the most common forms of underground buds found in many Australian plants. A lignotuber is a swollen under ground stem acting as a storage device. They are made strong by the presence of lignin; a plant polymer that gives large plants and trees their supportive strength (Raven, et al, 1999). As the plant grows the lignotuber is gradually deposited deeper into the soil. When the foliage is destroyed by fire, the lignotuber releases buds, which emerge to form the new shoot system. It is noted by McCarther (1965 in Gill et al, 1981) that 95% of the Eucalyptus species use lignotubers as a protective regeneration device. Other species of plants have similar structures in the form of root buds and rhizomes. Root buds are areas on the root system which, like lignotubers, start to produce new shoots when damage to the above ground foliage is sustained. A rhizome is a horizontal, often underground, stem that is very common in grasses and some ferns. They are extremely effective in vegetative propagation of the plant as well as offering some protection from fire due to their proximity to the soil. Grasses and ferns such as bracken re-sprout after fire (Trabaud, 1987).
Species that do not have lignotubers or a similar underground system commonly utilise aerial buds. In these species, the bud develops underneath bark. Upon defoliation of the plant, clumps of new shoots grow out from the main stem. Many eucalypts utilise this method of bud protection (Crane, 1972). The bark not only protects the buds but also the critical internal pathways used for water and nutrient movement from the heat of the fire. A similar principle is adopted by Pinus palustris. It protects its buds by covering them with many layers of extremely succulent non-flammable foliage to keep them cool and safe from fire. This, as with most adaptive traits, has its limitations and success depends on such aspects as the fire intensity and speed (Gill et al, 1981).
Unlike underground or aerial epicormic buds, which re-shoot the original plant, an adaptation called ‘serotiny’ gives rise to a new and often increased population of the plant (Trabaud, 1987). Several Australian plants, including the species of Eucalyptus regnans and Banksia ornata, share this ‘serotiny’ trait and have specialised seed capsules that are stored on the plant until fire triggers their release (E. Pharo pers. comm., 2000). The seeds are then deposited into well-lit and highly nutritive soil beds left over by the fire and the burning of the surrounding vegetation.
Many orchids, grasses, lilies and other small flowering herbaceous plants will not flower for many years and then burst into bloom when a fire moves through the area. Some orchid bulbs can lay dormant for up to 20 years waiting for a fire to bring it into growth (DPIEW, 2002). A number of factors could be responsible, such as high nutrient quality of the ash, increased light, and a decrease in competition for resources due to the reduction in neighbouring plants or even the chemicals in the smoke. In any case, fire aids or triggers the plants to reproduce indicating the ability of the species to not only survive fire but also actually harness it to increase their population. Xanthorrhoea australis and other plants within the genus show this fire stimulated inflorescent production method. Casuarinas and Oyster Bay pines cope well with low frequency fire, seeding in large numbers after fire (Chandler et al, 1991).
In contrast to plants, animals are mobile and can therefore move around to varying degrees and in most cases are able to escape the fire itself. Despite this ability to move around, certain animals can be restricted to a relatively small area due to their dependence on particular local biotic factors, like a particular food source or other physical conditions. Research indicates that in areas of Australia with regularly occurring, low intensity fires animals have evolved to be able exploit the burned areas (Chandler et al, 1991).
For an animal to survive a fire it has to avoid the flames, heat and smoke. This avoidance behaviour is one of the key adaptive traits. Animals living in fire prone areas have adapted to survive during the burn and immediately after when resources could be extremely scarce (Trabaud, 1987). Highly mobile animals like birds and kangaroos can generally move out of the fires path. Less mobile animals such as wombats and small mammals need to take refuge in the ground by burrowing or hiding in holes and depressions. Animal adaptations to fire prone habitats include being able to run or fly quickly and for long distances, burrowing, storing food and migration (Gill et al, 1981).
Some animals show quite specific behaviour to protect themselves from the effects of fire. The Acacia ant, Pseudomyrnex species, clears away all vegetation and debris from around the colony to stop it from been burnt and over heating. Other insects like the fire beetle, Merimna atrata, possess infrared radiation-detection organs that allow them to locate forest fires from distances of up to 160 kilometres away. They are attracted to the fire and the female lays her eggs into the charred wood (Chandler et al, 1991).
In contrast to animals such as the fire beetle, there are many animals that are adapted to fire prone environments yet do not necessarily have specific traits to allow survival of fire. For example, the Ground Parrot of southeastern Australia and southwest Western Australia lives in the coastal heath, which becomes uninhabitable if not periodically burned. Another fire prone environment specialist is the rat kangaroo, Bettong penicillata, which prefers the Casuarina species as its habitat. This habitat requires fires every seven or so years to be maintained. Research indicates that certain species that are adapted to these specialised niches would not survive should fire disappear from their area (Chandler et al, 1991).
Most animals living in fire prone areas might be better thought of as opportunistic rather than truly adaptive. In contrast, the previous discussion shows that plants have developed remarkable adaptations to surviving and even encouraging fire. Whether through adaptations or simply opportunistic behaviour, there are countless examples of animals and plants that that live and thrive in fire prone environments. Historical evidence suggests that fires have been shaping the land for many tens of thousands of years and in this time the flora and fauna have evolved to survive and utilise fire.
References. Chandler, C., Cheney, P., Thomas, P., Trabaud, L. and Williams, D. (1991). Fire in forestry Volume 1. Forest fire behaviour and effects. Florida: Krieger Publishing Company.
Crane, W. (1972). Fire in the environment. Symposium proceedings. USA: United States Forest Service.
Department of Primary Industries, Water & Environment. (2002). Fire and vegetation communities. Retrieved on September 2, 2002, from
Gill, A., Groves, R. and Noble, I. (1981). Fire and the Australian biota. Canberra: Australian Academy of Science.
Raven, P., Evert, R. and Fichholm, S. (1999). Biology of plants. New York: Worth Publishers.
Trabaud, L. (1987). The role of fire in ecological systems. The Hague: SPB Academic Publishing.