THE FINNIS REYNOLDS CATCHMENT
ABOUT THE PROJECT
Steered by Territory Natural Resource Management (TNRM), the Finniss Reynolds Catchment Group (FRCG) project has been operating since 2012 to address the problem of Mimosa pigra across the catchment.
The project engages and supports various people and organisations to share knowledge and resources in order to improve land management at a catchment scale through the physical management of the weed by undertaking aerial spraying and on-ground activities throughout the catchment.
FACILITATING STAKEHOLDER ENGAGEMENT
The catchment poses many challenges for stakeholder engagement and pest management activities as it is a large area, spanning across 5,500 square kilometres, that is comprised of Indigenous land, pastoral properties, national parks, crown land, weekender blocks and rural residential blocks.
MENACING MIMOSA IN THE
FINNIS REYNOLDS CATCHMENT
The floodplain pastoral properties of the Top End have been under threat from the prickly, pervasive weed, Mimosa pigra for many years.
In the Finniss and Reynolds River catchments the weed causes many land management problems as it reduces the biodiversity value of floodplain habitat, blocks access to cultural sites and reduces the grazing value of pastoral land by blocking stock from accessing pastures.
Mimosa seeds are water-borne and can reach floodplains from isolated plants and small infestations further upstream in drainage lines and billabongs.
As floodplain waters recede at the start of dry season each year, germinating seedlings become adult plants within a year, forming impenetrable thickets that produce huge banks of long-lived seeds. Seeds on the surface may germinate within a few months, but in addition, there are seeds which become buried in soil or leaf litter, and these may persist for twenty years or more, only germinating when the soil is disturbed.
Feral pig activity also intensifies the establishment and spread of Mimosa throughout the catchment.
Despite this, the project has successfully brought together and engaged land mangers and representatives from pastoral properties, Indigenous rangers, the Northern Land Council (NLC), Weeds Management Branch (NTG), Litchfield National Park, NT Land Corporation and various small property owners.
A Technical Advisory Group was used in the early stages of the project, to help guide best practice weed management in the catchment and buffer against knowledge losses occurring through management staff turnover on properties.
The group structure of the project has been an important aspect in increasing relationships and knowledge transfer between the people managing land in the catchment.
CHALLENGES TO TREATING MIMOSA
Colin Deveraux has many years of experience with Mimosa pigra management in the Finniss area. Starting on a small property on the north side of the river, he transferred his knowledge from there to Twin Hill Station on the broader Finnis floodplain, and later again to the Biodiversity Fund project.
Colin emphasizes that successful treatment of Mimosa is all about timing. Aerial herbicide spraying of Mimosa needs to specifically occur while the plants are actively growing, but also before flowering and seed set. Ideally, this is at the beginning of the wet season, as the rain helps new seedlings germinate and grow up high enough that they’re easy for the pilots to see in the pasture while they are undertaking aerial spraying.
Mapped Mimosa infestations throughout the catchment
However, every wet season is different, and some years there is only a small window to get the treatments carried out with optimal timing. If you go too early, the new plants coming up can get missed and grow throughout a whole season and make seed before a pilot comes by to spray again. On the other hand, you also want to avoid spraying at the last minute, as plants that are partially submerged in floodwaters do not die easily.
Therefore, it is critical to perform spraying treatments annually, at the appropriate time, without missing a year. It’s also very important to keep an eye out for Mimosa plants that don’t die despite being sprayed, so that these plants can be treated with alternate herbicides.
20 year herbicide treatment program at Twin Hill Station successfully sprayed all old growth Mimosa
70% reduction in feral pig population across the catchment
ACTIONS, PROGRESS & OUTCOMES
On Twin Hill Station, persistence against Mimosa pigra has paid off with herbicide treatment of all old growth Mimosa now completed after a long and extensive twenty-year treatment program.
Aerial spraying is also successfully being undertaken nearby at Labelle Downs and Welltree stations to keep central floodplain paddocks clear and push Mimosa back upstream along the Reynolds River. Furthermore, on Finnis River Station, floodplains continue to remain clear, with treatments focused on Mimosa pockets under paperbarks. While on Tipperary station, the focus is on treating all plants in the upper most parts of the Finnis Reynolds Catchment in order to reduce seeds coming down the river to Litchfield Station on the floodplain below.
While all properties have their own priority areas and works programs, overall the key ingredients to successful Mimosa treatment have been annual follow up prior to flowering, prevention of soil disturbance, and retention of good grass cover, which included the introduction of appropriate pasture grass species such as Olive hymenachne.
Additional activities undertaken within the Finnis Reynolds Catchment include:
the collection of baseline data on feral pig density and aerial culling of feral pigs to achieve a 70% reduction in targeted pig populations
the mapping of Mimosa infestations within the catchment
an increased establishment of biocontrol agents within the catchment
fauna surveys to identify priority fauna species in the area; and
annual aerial spray programs to treat large scale infestations of Mimosa each wet season
FUNDING & EXPENDITURE
Funds for the project have come from the Federal Government’s Biodiversity Round 1 Fund (2012-2017), the National Landcare Program, and most recently, contributions have been received from the Ichthys LNG Project and the Community Benefit Fund.
The mimosa aerial spray program has been a huge investment, with approximately $700K of Australian Government funding matched dollar for dollar by the pastoral properties in the catchment, between 2013 and 2017. Where properties have participated, it has taken between three and five years to see a reduction in the amount of treatment needed in a given paddock.
Expenditure of around $90 per hectare has been needed over five years to ‘reclaim’ areas from thick mimosa, which equates to a floodplain pasture protection value of around $20/hectare. Whilst treated floodplain areas continue to need ongoing annual investment to address the soil seed bank, this treatment is at a much lesser cost than the initial investment.