Natural values of Kakadu

Charles Darwin University; Kakadu National Park; Parks Australia - Australian Government

SITTGDE013 – Interpret aspects of local Australian Indigenous culture

7 Natural values of Kakadu

This section starts with a list of interesting weblinks, please visit and read the links below:

History and beauty from a geological perspective

Flora and Fauna

Weed management in Kakadu

For Park management purposes, a weed is defined as any naturalised (established and reproducing in the wild) plant that is not native to Kakadu.

Weeds compete with native plants for light, moisture and nutrients and often do not provide appropriate food and shelter for native wildlife. Particularly invasive weeds reduce plant and animal diversity, change burning regimes, and alter the structure, function and species composition of natural ecosystems.

Kakadu remains one of the most weed free conservation areas in Australia. Only a small number of weeds found in the Park are considered invasive: mimosa, salvinia, para grass, mission grass, gamba grass, candle bush, calopo, Gambia pea, golden shower, poinciana and coffee bush. Of these, mimosa, salvinia and para grass are given priority for control because of their potential to spread over large areas.

You can play an important part in preventing the introduction of weeds and minimising their spread-check your vehicles, trailers and equipment before entering the Park, keep to established roads and tracks, and don’t enter quarantine areas.

Mimosa (Mimosa pigra) is a Central American woody shrub that under ideal conditions grows up to four metres tall and is highly invasive. Large infestations are on the Adelaide River floodplain, the Daly, Finniss and Mary Rivers and on the East Alligator floodplain near Gunbalanya (Oenpelli).

Factors that contribute to mimosa’s success are a lack of natural enemies, a rapid growth rate, production of large quantities of easily transported viable seed, and a tolerance of drought and flood. Unchecked, mimosa forms impenetrable thickets across floodplains.

In Kakadu the threat posed by mimosa was identified early, and prompt action has meant that the Park is free of large mimosa infestations-it remains virtually an ‘island in a sea of mimosa’. Controlling the plant takes considerable resources: since the 1980s four people have been employed full time in the Park to locate and destroy mimosa by pulling out or mattocking small plants and applying herbicides to larger ones.

Salvinia (Salvinia molesta) and another noxious weed, the water hyacinth (Eichornia crassipes), were discovered in the Magela Creek system in 1983. The water hyacinth was successfully eradicated but salvinia spread rapidly into other tributaries of the East Alligator River and onto the Magela floodplain. Despite quarantining of the area and cooperation from the public, a new infestation was found in Nourlangie Creek in 1990. During the wet season salvinia is flushed out of Nourlangie Creek into the South Alligator River.

A biological control agent, the weevil Cyrtobagus salviniae, was introduced soon after salvinia’s discovery. It effectively controls the weed most years. Towards the end of the dry season the weevil population rapidly decreases because most of the salvinia has been eaten. During a poor wet season, high nutrient levels cause the salvinia to grow faster than the weevil population can regenerate. This results in a blanket of salvinia over the water, but as the weevil numbers increase the salvinia is reduced later in the year.

With the help of the CSIRO division of entomology, a management plan has been developed to closely monitor the weevil’s effect. Floating booms are also used to contain salvinia, and occasionally a low-impact herbicide is used to prevent excessive build-up of the weed and reduce the chance of it spreading further.

Para grass (Brachiaria mutica) was introduced to the area as pasture grass in the 1930s. Like mimosa, para grass can take over huge areas of floodplain, growing vigorously when grazing pressure is reduced and after burning. The grass is quickly filling in a number of Kakadu’s wetlands and threatening wildlife habitats. Biological control is not an option at the moment since para grass is still being promoted as a valuable pasture grass for cattle outside the Park. Control involves pulling out small infestations and using herbicides in larger areas.

Management of feral animals in Kakadu

Feral animals in Kakadu are animals introduced by non-Aboriginal people, that were once either domesticated or native to another country and that now lives and breeds in the Park. Among the feral animals in Kakadu are Asian water buffaloes, cattle, pigs, horses, donkeys, cats, dogs, rats, mice, house geckos and European bees. Cane toads were recorded in Kakadu for the first time on 12 March 2001.

The management objective for feral animals in Kakadu is to limit, as far as possible, their adverse effects on the environment while taking into account the views and economic interests of traditional owners.

Buffalos in Kakadu

Asian water buffalos were introduced into northern Australian settlements between the 1820s and the 1840s, as work animals and for meat. As these settlements were abandoned, the buffaloes were released and quickly spread across the lowlands of the Alligator Rivers region.

By the 1960s buffalo numbers had reached enormous proportions and the damage they were causing was obvious. Buffalos cause damage in a number of ways. Their sheer size, weight and hard hooves compact the soil and inhibit plant growth, causing erosion. Their habit of wallowing erodes river banks and muddies the water, making it unsuitable for many aquatic plants and animals. They eat large volumes of grasses and other plants, competing directly with native wildlife. And as they move from one wetland area to another they create ‘swim channels’: where these channels intersect with tidal creeks, saltwater is able to move into freshwater swamps, often killing a number of plants and animals intolerant to saltwater.

Buffaloes carry tuberculosis, which can be spread to domestic cattle. Because of the severe implications for the export meat industry, the Brucellosis and Tuberculosis Eradication Campaign was established nationwide to eradicate feral cattle and buffaloes from all areas. The Campaign provided funding to reduce buffalo numbers in the Park. The removal of buffaloes from Kakadu National Park began in 1979. Of an estimated population of 20 000 buffaloes, it is thought that only a few hundred remain (Press et al. 1995).

The difficult nature of the country and the consequent costs make total eradication almost impossible. The Brucellosis and Tuberculosis Eradication Campaign ceased at the end of 1997. As a result Park staff have taken over responsibility for monitoring and controlling the buffalo numbers. Since the reduction in buffalo numbers degraded areas have recovered dramatically. There are fewer buffalo wallows, there is clear water in billabongs, there is less salt intrusion, and plants such as red water lilies, grasses and sedge plants-valuable food for native animals-are reappearing.

Buffalo has become an important part of the diet of Aboriginal people in the region. A small herd of domesticated buffaloes is retained in the Park to provide meat for Aboriginal traditional owners.

Other feral animals

Pigs cause damage to a broad range of Kakadu’s habitats. They degrade the environment around springs and small rainforest patches, especially in the wet season. They also dig up areas in their search for food and compete directly with magpie geese and Aboriginal people for bulbs that grow along the wetland shores. The ground they expose is vulnerable to weed infestation-pigs are thought to be the main agents of spreading the weed mimosa through the Park. Park staff control pigs close to known mimosa infestations on an opportunistic basis and feral pig control work is conducted regularly.

Horses are particularly common in the southern woodlands of the Park. They spread weeds and damage waterholes by eroding soil and fouling the water. Recent control measures have reduced the number of horses along the Kakadu Highway.

Cats are present in low numbers throughout the Park. Casual observations and research from southern Australia suggest that cats’ hunting activity is having a detrimental effect on native wildlife. Cats are not allowed to be kept as pets in the township of Jabiru. They are shot by Park staff each wet season along floodplain and creek margins. Again, this is done on an opportunistic basis.

Dogs that have become feral have some impact in that they interbreed with the dingo population in the Park, changing the dingo gene pool. Jabiru residents are allowed to keep up to two dogs within the confines of the township and Park residents can keep dogs at the discretion of the Director of National Parks.

Cane toads were found in Kakadu National Park on 12 March 2001.
Cane toads are poisonous throughout most of their life cycle and current information suggests that they will have an initial impact on animals such as snakes, goannas and quolls, who will try to eat them. Evidence from other areas affected by Cane toads suggest numbers will stabilise after an initial period. No effective control measures are available. Cane toads in the Park are likely to be one of the most pressing management problems facing Kakadu in the coming decade.

Interesting links showing more about Kakadu’s natural value.

Gallery of animal images
Freshwater fish of Kakadu
Estuarine fish of Kakadu
Scenery pictures of Kakadu