Threats to Australian Plants
Background
When botanists Joseph Banks and Daniel Solander set foot on the east coast of Australia in April 1770, they entered a botanical paradise. By chance, the landfall of Captain James Cook's "Endeavour" coincided with one of the most botanically rich areas of Australia and Banks and Solander spent countless hours collecting and drawing the numerous new plant species that confronted them. Earlier collections had been made by Dutch explorers on the west coast but the collections made during the voyage of the "Endeavour" were far more comprehensive and extensive.
In the 200+ years following European settlement, the Australian flora has suffered greatly in the name of progress. Surprisingly, the flora around the original settlement at Port Jackson has suffered somewhat less that is the case in many other parts of the country. This can be attributed to the fact that the rugged sandstone topography has made large-scale development an expensive proposition. Overall, however, it is believed that around 76 plant species have become extinct during the two centuries since European settlement with approximately another 301 species being at serious risk in the short term. Of course, no one knows how many species may have been lost before they were botanically described.
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| Top: Acacia pubescens - at risk through too frequent fires. Bottom: Hakea bakeriana - at risk through lack of fire. Photos: Brian Walters | |||
Plant loss occurs through a variety of mechanisms not always due to human intervention. Natural processes may result in climatic changes which can lead to extinction or gradual evolution of species as they cope with the changed conditions. These are long term effects which may take place over millions of years. In contrast, plant loss due to human activities are far more dramatic and can produce irreversible effects in a few decades.
In 1984, Leigh, Boden and Briggs (see Further Information) described the main recognised threats to Australian plants and the number of species effected by each threat. These are:
- Grazing
- Agriculture
- Forestry
- Roadworks
- Mining and Quarrying
- Urbanization and Industrial Development
- Horticultural Collecting
- Fire (including lack of fire)
- Competition
- Herbicides
- Low Numbers
In addition to these, a range of other threats include recreation, rubbish dumping, railway maintenance, water storage, insect attack, erosion. A number of species are effected by more than one threat.
Most of the impacts of human activities are obvious. It's not difficult to imagine the effect that urban development, quarrying, roadworks and agriculture might have on a rare plant in the area being developed. Other threats are more subtle in their impacts. For example:
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| Phaius tancarvilliae - at risk through horticultural collecting. Photo: Keith Townsend |
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- Fire - This is one of the more misunderstood factors in the Australian environment. The widely held view is that "the bush regenerates after fire". Unfortunately this is only partly true and both the frequency and intensity of fire can have a marked impact on the composition of the flora in a particular area of vegetation.
Some plant species rely solely on seed for their regeneration after a fire (other plants may be able to regenerate by vegetative shoots from the roots or from the burnt stems). Most plants require a number of years following germination before they reach maturity and are able to flower and set seed. If fire occurs more frequently than the time that the plants take to mature, the plants may be eliminated from the particular area. This is a factor that must be considered by bushfire control authorities who routinely initiate "control burns" for the protection of property. Threatened plants in this category include Acacia pubescens, Banksia lullfitzii, Persoonia rudis and Tetratheca remota. Some other plant species, such as Hakea and many banksias, depend heavily on fire for regeneration. These are species which retain seed within woody capsules which remain closed until stimulated to open by the heat from a bushfire. Other plants threatened by lack of fire include Swainsona laxa and Swainsona recta.
- Horticultural Collecting - Unfortunately there are people in the community who "must have" particular plants in their collections and who are quite prepared to remove plants from the wild irrespective of the rareity of the plants or their chances of survival in cultivation. Large scale collection also occurs by people out for "a quick buck". Threatened species in this category include Eucalyptus rhodanthe (rose mallee), Calochilis richae (bald-lip beard orchid) and Phaius tancarvilliae (swamp lily).
- Low Numbers - There is usually a lower limit to the numbers of plants in a population below which the viability of retaining the species in the long term is dubious irrespective of the degree of protection provided. One unforeseen event such as fire or unauthorised clearing could see the entire population wiped out. Threatened species known to exist in excessively low numbers include Grevillea batrachioides (WA), Grevillea rara (WA), Logania insularis (SA), Owenia cepiodora (Qld/NSW) and Wollemia nobilis (Wollemi pine - NSW).
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| Grevillea batrachioides - at risk through low numbers existing in the wild. Photo: Brian Walters | |||
Further information on the key threatening processes affecting the Australian flora can be found on the website of the Department of the Environment, Water, Heritage and the Arts (see Further Information.)
Thanks to John Wrigley, Cas Liber, John Atkinson and Angus McLeod for providing comments and suggestions.