Lantana (Lantana camara L.)
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2.3 Lantana impactsLantana is classed as a weed in more than 60 countries (Swarbrick et al. 1995) and is considered to be one of the ten worst weeds worldwide (Sharma et al. 2005). It infests millions of hectares of grazing land globally and is of serious concern in 14 major crops including coffee, tea, rice, cotton and sugarcane. It was declared a Weed of National Significance in Australia because of its widespread distribution and impact on agricultural industries and biodiversity. Lantana costs the Australian grazing industry more than $104 million in lost production and $17 million in management efforts every year (2005–06 values) (AECGroup 2007). The majority of these costs are associated with reduced livestock-carrying capacity, increased property maintenance expenditure and stock poisoning. In commercial forests, lantana raises production expense, increases the risk of damage by fire and impedes access. For example, it is estimated that lantana accounts for 30 per cent of the establishment costs and up to 50 per cent of harvesting costs of hoop pine plantations in south-east Queensland (Wells 1984). In addition, the invasion of natural ecosystems by lantana puts at risk populations of more than 1400 native species, including 279 plant and 93 animal species listed as rare and/or threatened under state and federal legislation (NLMG 2010). In Queensland alone, approximately 107 000 hectares of endangered regional ecosystems contain lantana (DERM 2010). Where infestations are dense, lantana excludes native species through smothering and allelopathic effects (Gentle & Duggin 1997b). It dominates understoreys, prolongs succession and reduces biodiversity (Fensham et al. 1994; Gentle & Duggin 1997a; Lamb 1982; Stock & Wild 2006; Swarbrick et al. 1995). Not all the impacts of lantana are negative. It provides a substitute habitat and food source in highly disturbed environments for some fauna, and despite Australia-wide restrictions on sale and distribution, lantana still has limited social value as an ornamental plant. These positives must be recognised so that management and education programs can be adapted to avoid further damage. However, on balance, the impacts of lantana are overwhelmingly negative. To encourage a change in attitudes and commitment to lantana management and control, it is important that the public are made aware of this fact and inspired through evidence that action does achieve positive and measurable outcomes. 2.4 Control methodsThere are a range of control methods suggested for lantana, including manual, mechanical and chemical removal; as well as land management techniques that promote competition. However, the validity of each technique and the manner in which they should be integrated is determined by site-specific circumstances. Consequently, it is recommended that land managers refer to the Lantana best practice management and decision support tool (Stock et al. 2009) for more detailed information. Although there are now management techniques available for the majority of circumstances, options are still limited for hard-to-access areas and for the control of stressed plants. There are also major gaps in knowledge about implementation of fire management across the range of environments in which lantana grows. In addition, there are gaps in our knowledge of lantana’s ecology and biology, and current long-term research of population dynamics aims to determine the most vulnerable points of the life cycle to target with traditional and biological control methods.
2.4.1 Biological controlLantana was the first weed in the world to be the target of a comprehensive biological control program, when 23 insect species collected from Mexico were introduced to Hawaii in 1902 (Walton 2005). It was also the focus of Australia’s first biological control program, with the introduction of four insects to Australia in 1914 (Walton 2005). To date, 18 of the 31 biological control agents that have been introduced to Australia have established successfully. These agents have varying impacts on the growth and fecundity of lantana populations, but as yet none have provided effective control (Zalucki et al. 2007). Horticultural hybridisation has produced an estimated 650 phenotypes of lantana throughout the world (Day et al. 2003). Observations of differing host specificity between varieties of L. camara suggest that the collection of new biological control agents from plants of genetically similar origin may increase the success rate of control programs. Unfortunately, due to hybridisation, there are no naturally occurring species of lantana that genetically match Australian varieties. However, recent research has indicated that Australian L. camara populations have their genetic origins in the Caribbean and Venezuela (Watts et al. 2009); consequently, these countries could be targeted for collecting biological control agents. It has also been recommended that future biological control research programs may be improved by targeting insects that feed on stems and roots, in addition to the existing leaf and flower feeders (Zalucki et al. 2007).
2.5 Socioeconomic factors affecting managementWidespread weeds such as lantana pose significant barriers to effective management because of the cost and time associated with control. Together with the serious impacts caused to economic and environmental systems, management can seem an insurmountable challenge causing flow-on social and psychological effects to individuals and communities. Surveys of production land managers in 2003 and 2006 indicated that the major limiting factors to the adoption of control are time (74.3 per cent of respondents in 2003 and 74.5 per cent in 2006), cost of control (49.0 per cent in 2003 and 34.1 per cent in 2006) and difficulties due to terrain or accessibility (39.8 per cent in 2003 and 47.5 per cent in 2006) (AECGroup 2007b). Although these surveys represent only a portion of the groups involved in managing this weed, barriers to control are likely to be similar across groups. In environmental systems, lantana performs a limited number of ecosystem functions through the provision of food and habitat to fauna in disturbed environments. Although it is recognised that the negative impacts of this weed far outweigh the positives, further research and extension in this area is vital to give conservation land managers the confidence to manage this weed without causing further ecosystem damage. Finally, there is a section of the population that remains either ignorant or unconcerned about the impacts of lantana. If livelihoods and lifestyles are not directly impacted, competing priorities usually hold sway. This trend is causing increasing issues in peri-urban areas where weed infestations on lifestyle blocks can impact adjacent farming communities and environmental systems. Clark et al. (2004) identified four needs to ensure that increased management occurred:
The lantana WoNS initiative has been working toward these goals, but will require sustained focus from stakeholders to achieve long-term attitudinal and behavioural change. |