Managing threats to floodplain biodiversity and Indigenous values

This research looked at the extent and spread of the exotic grasses para grass and olive hymenache on the floodplains within Kakadu National Park and how this is impacting on the Indigenous values of floodplains.

These dense weed grasses have significant negative impacts on floodplain ecosystems and negatively impact on the ability of Indigenous Traditional Owners to access floodplain resources.  The research also examined a range of potential management strategies.

Kakadu National Park’s floodplain wetlands are rich in biodiversity and hold great cultural significance for Indigenous Traditional Owners. To this day, Traditional Owners continue to fish, hunt and gather bush tucker on floodplain areas.

Para grass and olive hymenache are exotic grasses which were first planted in Kakadu National Park in the 70s and 80s to feed livestock. They now pose a serious threat to floodplain biodiversity because they spread very quickly and choke out native grasses, destroying aquatic habitat and reducing food for native fauna in the process.

They also have about twice the dry season fuel load of the native grass wild rice, making fires much hotter, which threatens turtles that nest in the floodplain soil during the dry season.  These dense grass infestations impact on Traditional Owners by making it harder to hunt and gather important floodplain resources.

The first step of the research was to determine the extent of the weeds and how quickly they were spreading. The team undertook helicopter-based aerial surveys of all of Kakadu’s floodplain areas.  Researchers then used the maps of the current pattern of invasion together with knowledge about the history of past invasion to build a model that predicts future patterns of spread. The team also collected information on the cost of different management actions to create a model that can test both the cost and effectiveness of different weed management strategies.

To understand which floodplain areas were most important to Traditional Owners and what impacts the weeds were having on Indigenous livelihoods, the researchers sought input from Traditional Owners affiliated with the floodplains of Kakadu. Thirty-seven Traditional Owners helped to describe and map areas of cultural and economic importance, such as sites used for hunting and fishing.

The results of consulting traditional owners showed that almost a quarter of the floodplains were being used for hunting and gathering. Many of the participants were able to describe the harmful impacts of these weeds first-hand, describing how floodplain areas are being damaged and how the exotic grasses are making it much harder to collect floodplain bush tucker in those areas.

A model was developed in order to compare the future patterns of invasion if different weed management activities were undertaken. The project team evaluated the performance of several strategies in Kakadu over a 20-year period. The model includes management costs and can help Park managers plan their weed management activities and make strategic choices about investments in weed control over many years.

The first strategy evaluated was simply no additional management, which was used as a base from which to compare the other scenarios. The second involved a strategic weed management approach to contain and control infestations. The last scenario considered the same management approach, with the addition of actions to help Traditional Owners regain access to important bush tucker sites, which have become overrun by weeds. The strategy that supported both weed management and Indigenous values would deliver the greatest cultural and biodiversity benefits.

The research focused on the floodplains of Kakadu National Park, including Magela Creek floodplain, selected floodplains of the West Alligator River, and the Boggy Plain-Mamukala-Yellow Water floodplain system of the South Alligator River