Queensland Primary Industries and Fisheries Minimising the risk of spread of Mimosa pigra from Peter Faust Dam, Proserpine Edward Attard, Cassandra Chopping, Peter Austin, Jason Williams and Tony Pople � Final report to the Department of Agriculture Forestry and Fisheries and the Department of Environment and Heritage May 2006 Edward Attard and Tony Pople Land Protection, Department of Natural Resources and Water GPO Box 2454, Brisbane Qld 4001 Cassandra Chopping and Peter Austin Land Protection, Department of Natural Resources and Water PO Box 63, Mackay Qld 4740 Jason Williams SunWater, 126 Giddy Road PMB 5013, Ayr Qld 4807 Published by: � ©State of Queensland (Department of Natural Resources and Water) 2006 � ii Risk of Mimosa pigra spread in Queensland � Contents Summary and recommendations v � Section 1–Overview of Mimosa pigra ecology, distribution, impacts and management 1 � 1.1 General introduction 1 � 1.2 Global distribution and history of introduction to Australia 2 � 1.3 M. pigra life history 2 � 1.4 Potential distribution in Australia 4 � 1.5 Current and potential impacts in Australia and overseas 4 � 1.6 Control options and cost 4 � Section 2–Management of Mimosa pigra in Queensland 5 � 2.1 Introduction 5 � 2.2 State wide strategy 6 � 2.3 Management of M. pigra at Peter Faust Dam 6 � 2.4 Research on M. pigra in Queensland 11 � 2.5 Key stakeholders and their responsibilites 11 � Section 3–Assessing the risk of Mimosa pigra spread from Peter Faust Dam 13 � 3.1 Introduction 13 � 3.2 Methods 13 � 3.3 Vectors of seed spread 17 � 3.4 Management options 21 � 3.5 Ranking management options 25 � 3.6 Making management decisions 27 � 3.7 Monitoring and performance evaluation 27 � Acknowledgments 28 � References 29 � Appendixes 31 � Risk of Mimosa pigra spread in Queensland � iii iv Risk of Mimosa pigra spread in Queensland � Summary and A number of preliminary recommendations can be drawn from this risk assessment: recommendations Monitoring and control In February 2001 the first infestation (~100 plants) 1. Current monitoring and control of M. pigra must of Mimosa pigra in Australia outside the Northern be continued, including washdown of vehicles and Territory was found at Peter Faust Dam, near identifying tracks as ‘clean’ and ‘dirty’. However, Proserpine, in central coastal Queensland. This shrub monitoring could be more strategic. Greater effort continues to have major environmental, economic can be directed to periods when germination is and social impacts on the coastal floodplains of most likely and in higher density areas the Top End of the Northern Territory, where it forms (i.e. temporal and spatial stratification). Access dense, almost monospecific stands. At risk of invasion to areas with M. pigra seed and the high detection by M. pigra in central Queensland are canefields, probability of M. pigra seedlings needs to be cattle-grazing areas and wetlands of conservation maintained by clearing Melaleuca regrowth. significance. 2. Although considered a low priority, monitoring of In 2001 a stakeholder group was assembled, downstream areas is needed if new incursions are comprising the local cattle grazier, SunWater to be identified before their eradication is no longer (which is responsible for management of the dam), feasible. Such delimitation is an important criterion the Queensland Cane Growers Organisation Ltd for eradication. This is likely to be best achieved (Canegrowers), Whitsunday Shire Council and the through a combination of direct monitoring using Queensland Department of Natural Resources and trained surveyors and educating landholders in Water (NRW). Over the next five years the group identifying M. pigra and the risks associated with oversaw a range of on-ground activities to eliminate its spread. M. pigra from the site. This work included describing Livestock management aspects of the biology of M. pigra at the site, investigating control measures and regular monitoring 3. As a high priority, cattle that have been grazed in of the site and removal of plants. However, the M. pigra-infested areas should be held in presence of vast numbers of M. pigra seed in the soil M. pigra-free paddocks for at least seven days at the dam and their likely persistence for more than before transport, as practised in the Northern 20 years means that the potential ways that this seed Territory. A formal agreement is required between could move from the dam (‘vectors’ of seed spread) the local grazier and government to cover need to be identified and managed. These vectors additional costs. include fluctuating water levels, wildlife, cattle and 4. The highest risk (i.e. high M. pigra seed density) recreational users of the dam, particularly fishers. area. on the south-western shoreline, should ideally In mid-2005 a risk assessment involving the major be fenced to exclude cattle, but was considered a stakeholders was therefore conducted to identify and lower priority than other management options. evaluate these vectors and then to canvass a number Restricting access of management options to minimise the risk of 5. Currently recreational users have physical access to M. pigra seed spread. These options were then ranked most areas of the dam. The difficulties of policing according to the risk (likelihood × consequence) of necessitate restricting road access to the higher risk seed spread from a particular vector and the feasibility areas through fencing and locked gates as a high of managing the vector. The latter considered the priority. Access to the western shoreline by boats sociopolitical, economic and technical feasibility of is more problematic, requiring good signage and implementing each management action. identification of the prohibited area perhaps using A further meeting among stakeholders is required to marker buoys. review the risks of potential vectors, the management Education options, their scores and resultant ranks. To be efficient, limited funds should be allocated to 6. Recreational users of the dam need to be made management options that generate the greatest better aware of M. pigra, its impacts and how it can reduction in overall risk of weed spread. Stakeholders, be spread. There are now several warning experts and managers therefore need to compare the signs around the dam, but there needs to be cost of options and their ability to reduce risk. greater exposure of the problem in the media. Risk of Mimosa pigra spread in Queensland � v Pig control 7. As a high priority, pig hunting (other than by authorised hunters) should be banned and 1080 baiting used to control numbers. Compliance 8. An awareness campaign, restricting access and banning pig hunting will all fail unless they are supported by policing the movement of people within the dam area. Enforcing these restrictions is difficult and could require anemergency quarantine notice that stipulates how the dam can be used and allows authorised officers to police use of the dam and issue fines. Performance evaluation 9. Monitoring is required to determine the effectiveness of management action. Appropriate indicators to monitor are likely to be reductions in the activity of people, pigs and cattle in the M. pigra-infested areas, use of washdown facilities and the survey effort downstream of the dam. vi Risk of Mimosa pigra spread in Queensland � Section 1 Overview of Mimosa pigra ecology, spreads into its potential distribution area, which distribution, impacts and management includes wetlands throughout northern Australia. Working against this effort is the vast number of 1.1 General introduction M. pigra seed in the soil, some of which may remain viable for more than 20 years (Lonsdale 1992). An infestation of Mimosa pigra was discovered at This long timeframe increases the risk of seed Peter Faust Dam (see Section 2) near Proserpine in being transported outside the site. This report central coastal Queensland (Figure 1) in 2001. This describes an assessment of this risk and how it can is the first known Australian infestation of this weed be best managed. outside the Northern Territory, where it has major Section 1 of this report provides an overview of the environmental, social and economic impacts. Similar problem, including relevant aspects of the ecology impacts are possible in Queensland where it might of M. pigra. Section 2 describes the current invade canefields, cattle-grazing areas and wetlands management of M. pigra at Peter Faust Dam. of conservation importance. Section 3 presents the risk assessment, which uses Fortunately the outbreak at Peter Faust Dam appears stakeholders to identify various hazards, their risks to have been contained in the immediate area around and potential management options. the dam, thus providing a good chance of eradication. Over the five years since 2001 managers undertook monitoring, removal and research of M. pigra at Peter Faust Dam in an attempt to eradicate the weed. The program is costly, but is offset by the cost of potential impact and ongoing control if the weed Figure 1. Location of Peter Faust Dam in central coastal Queensland Risk of Mimosa pigra spread in Queensland � 1 1.2 Global distribution and history of 1. M. pigra can withstand the anaerobic conditions of introduction to Australia inundation and flooded soils by having roots near the surface to take up oxygenated water (Miller, The native range of M. pigra is central and southern Nemestothy and Pickering 1981). At Peter Faust America, spanning the tropics from northern Mexico Dam M. pigra was originally found growing in o o (~25 N) to central Brazil (~23 S) (Walden et al. 2004). more than five metres of water (Figure 3) and later It has spread throughout the tropics, including in areas of Melalaeuca with large mats of aerial Australia (Figure 2). It was probably introduced to roots where water levels had receded (Figure 4) Australia in the 1870s, either accidentally in seed (Chopping 2004). samples for the Darwin Botanical Gardens, as seed 2.