Assessing the Risk of Mimosa Pigra Spread from Peter Faust

Section 3 Assessing the risk of Mimosa pigra identify the inherent risk for each potential vector, spread from Peter Faust Dam current mitigation, residual risk (i.e. risk remaining given present management action) and what options 3.1 Introduction were available to address this residual risk. For this exercise NRW staff were divided into regional This section of the report addresses the question of managers and research scientists. The risk of an how best to allocate finite funds in the management adverse event such as the spread of M. pigra seed of M. pigra at Peter Faust Dam. Regular surveys of the can be considered as its likelihood multiplied by its perimeter of the dam, combined with good access consequences. Some vectors could have different tracks and clearance of Melaleuca for detection of consequences. For example, wildlife might move seed M. pigra, are clearly required to ensure no further higher up the catchment, whereas water flow will move production of M. pigra seed. These are a high priority seed directly down the catchment, where impacts are for management and are not considered here as likely to be greater (see Section 1.5). For the vectors negotiable or optional activities, but were nevertheless examined here, the likelihoods and consequences ranked with other management actions. However, the were not considered separately. long-term persistence and vast amount of the seed in the soil will require monitoring for possibly more than An initial workshop was then held in Proserpine in 20 years. This also means that there is a reasonable September 2005 to enable face-to-face discussion of chance of seed being transported outside the dam each vector and the potential mitigation measures. site. The possible routes of transport were identified A scoring system was used to assess the feasibility and the associated risk was assessed through a series of various management options. Some stakeholders of meetings with stakeholders. Options for managing (i.e. Proserpine Chamber of Commerce and tour these hazards were then considered, along with the operators) were unable to attend the workshop, feasibility of implementation. so their input came through face-to-face meetings with NRW and SunWater staff. The results of this 3.2 Methods workshop were circulated in a draft of this report and a further workshop was conducted in March 2006 Conducting risk assessments by using expert with participants having a greater familiarity with the judgement and involving stakeholders has become risk-assessment process and a longer time to consider common practice in environmental management alternative management options. Risk scores, the (Burgman 2005). The approach taken here draws scoring system to assess feasibility of management on these experiences. The six stages of this risk options, and the resultant scores were reassessed assessment, shown in Figure 14, involved close and alternative management options identified at this interaction with all key stakeholders (see Section 2.5 workshop. and Appendixes 1 and 2). The potential pathways for seed transport away from the dam were first identified At the September 2005 workshop, management by NRW officers and SunWater staff. These are options were given a feasibility score out of 10 using ‘hazards’ in risk-assessment terminology (Burgman part of a system for assessing feasibility of controlling 2005), but are given the more specific term ‘vectors’ pest impacts in Queensland (Walton 2005). A here. Vectors are usually considered as carriers of management option is feasible if it has widespread disease, but have been used more broadly to include community and government support, it is relatively weed seed transport (e.g. Walden et al. 2004). Initially inexpensive, it is logistically possible and it is effective these vectors were split into those associated with at reducing pest impact and not simply reducing pest moving seed within the dam and vectors moving seed population size. For each management option, points away from the dam. This dichotomy was subsequently were allocated for each of 12 attributes covering seen as largely unnecessary as the vectors and sociopolitical, technical and financial aspects of the associated management actions were generally the option (Table 1). This latter assessment is consistent same, although the consequences were different. with the national post-border weed risk management protocol developed by the Weeds Cooperative This list of potential vectors was mailed to all Research Centre (Virtue et al. 2005) and weed risk stakeholders prior to a workshop to see if any vectors assessments conducted in other states had been missed, to score the risk of each vector (e.g. Virtue 2004). Higher scores in Table 1 reflect on a scale of 1–10, and to consider the current and greater feasibility of management. Most attributes potential mitigation measures (i.e. management are self-explanatory. The difficulty was modifying actions) for each vector. Participants were asked to Risk of Mimosa pigra spread in Queensland � 13 the original attributes in order to apply them to Participants at the workshop were broken into management options to reduce risk, rather than groups to work on sets of management options. Each following their original intention to more generally group then reported back to the workshop, enabling control a pest across the entire state. A description of participants to contribute to the assessment of all some attributes is therefore given below. options. The advantage of using a scoring system • Of the sociopolitical attributes, landholder over, for example, subjective judgement is that it is support refers to the extent to which landholders transparent and to some extent repeatable, allowing (i.e. SunWater and the local grazier) would have to a large number of attributes to be examined together change present management practice and whether and easy comparison of management options. An they would consider the change worthwhile. equal weighting was given to sociopolitical, technical and financial attributes, but this could also be • State government commitment refers to all agencies reworked. While the assessment is quantitative, some whose support would be required. attributes will be poorly known for a management • Under technical and financial attributes in the option and attribute scores will vary among assessors. original use of this scoring system (Walton 2005) The source of variation can at least be readily a contrast is made between the technical ability identified and the score reassessed with more to reduce numbers (i.e. a high proportion of the assessors or with better information. If an attribute population) and the ability to reduce the financial for a management option was unknown, it was given impact. For this study the contrast is of the ability a low feasibility score of 1. Thus the assessment was to simply stop seed movement (or remove seed or biased towards better known management options. plants) with the ability to reduce the risk of seed A further benefit of using a scoring system is that it spread. These might differ if the management identifiesthose attributes that need to be addressed if option cannot target a high-risk activity or area. the option is to be more seriously considered. • Only some life stages (e.g. adults versus seeds) Scores for the 12 attributes of feasibility were added, of a pest may be susceptible to or targeted by a and then divided by 30 to give a value out of 10 to management action, and so these management be on the same scale as the risk score (see above). options are less feasible than options affecting all The feasibility score was then multiplied by the risk life stages. For M. pigra there are three relevant score to give a total score out of 100, which can be life stages: a long-lived seed bank, seedlings and used to compare and rank management options. For mature plants. Most of the management options this calculation an average risk score was required for considered in this report attempt to reduce the risk each vector from the range offered by stakeholders. of seed spread through stopping actual transport This average was determined from a separate of seed. However, detection and removal of meeting between NRW officers and SunWater. The seedlings and adult plants are obviously important score represented a weighted average based on each in reducing the risk of further seed production and stakeholder’s expertise. therefore seed spread. • Logistics of implementation refers to the influence of such things as access (e.g. remoteness, terrain), number of personnel required and equipment on the ability to carry out the option. • Surveillance refers to monitoring compliance with and the effectiveness of the management option (e.g. change in the number of illegal campers as a proportion of all visitors). • Duration of the action refers to whether the management option requires ongoing input (e.g. policing use of the dam at all times), periodic input (e.g. policing only during peak visitation periods) or is a single event (e.g. erection of a sign or fence). Assessing this attribute can be problematic because management options are not mutually exclusive and it is difficult to assess options such as signs, fencing and policing in isolation. Interactions between options should therefore also be considered. 14 Risk of Mimosa pigra spread in Queensland � Table 1. Attributes and associated scores (out of 25) used to assess feasibility of management options. For each management option, scores were then

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