Management of Chrysanthemoides monilifera subsp. rotundata in Western Australia

Abstract

One of Australia's most serious weeds, Chrysanthemoides monilifera subsp. rotundata (bitou bush) was recently found for the first time in Western Australia as a well established population in Kwinana, a major port and industrial area south of Perth, the State's capital. This population is remote from other bitou bush infestations in Australia and had escaped detection despite extensive surveys in the same State for the other subspecies that is present in Australia, Chrysanthemoides monilifera subsp. monilifera (boneseed). The main reasons it went undetected are thought to be the tightly controlled access to this area because of mineral processing and port activities, the unusual invasion route via a heavy industrial area and the morphological similarity to a native species when it is not flowering. Two surveys defined the core population of 1038 plants that are spread along the coast over a 25-ha semi-circle with about a 500-m (1640 ft) diameter. Subsequent surveys of first a 500 m buffer zone and later a 1-km (0.621 mi) buffer found four additional plants, indicating that there is considerable potential for dispersal. We concluded that the survey has not delimited the distribution because of the potential and evidence for long distance dispersal. Cooperation by the various land managers has led to all plants being killed, as an initial step to management of this species. Other steps to be undertaken include an awareness campaign in the area that would need to be surveyed for delimitation of the spatial distribution and seed bank assessment to measure potential dispersal both in space and through time. It remains to be determined what is the best strategic response: eradication or containment.

Long term monitoring of recruitment dynamics determines eradication feasibility for an introduced coastal weed

“…T. Norl. (Asteraceae; hereafter, bitou bush), as a well-established population in Kwinana, a major port and industrial area near Perth, Western Australia (Weiss et al 1998, Scott andBatchelor 2014). Our initial surveys in 2012 documented a restricted extent for this bitou bush incursion, aside from the potential for seed export from the site (Scott and Batchelor 2014).…”

“…The focal population was located in the Kwinana region of Perth, Western Australiaan industrial port area with mixed land-use, including fragments of low-quality native vegetation, and high levels of industrial goods traffic on and off-shore (32°12.652'S, 115°46.018'E). Scott and Batchelor (2014) provides details on the context of the focal population, including local climate, landscape and features that influence delimitation and detection. Initial surveys of the population started in September 2012 (Scott and Batchelor 2014), continued through 2013 and were repeated each year in March and April from 2014 to 2018 (Figures 1,2).…”

“…The Kwinana bitou bush population has existed, as verified from aerial photography, since at least 1995 (Scott et al 2019). The Kwinana population is unusual because the nearest populations of bitou bush are found more than 3,000 km to the east as an introduction in eastern Australia, or more than 8,000 km to the west as a native species of southern Africa (Scott and Batchelor 2014). This specific context makes it feasible to consider eradication as a management goal for bitou bush in WA, rather than local extirpation where there is a possibility of recolonization (Wilson et al 2017).…”

The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa

“…), with more recent studies continuing to emphasize seed recovery location as the only means of determining seed dispersal distances (e.g. Scott & Batchelor ). This approach provides limited understanding of rare long‐distance dispersal events when compared with a contemporary vector‐based approach that utilizes vector characteristics and behaviour to determine seed dispersal distances (Nathan et al .…”

“…A traditional seedcentred approach to understanding dispersal has inferred dispersal distances from fruit/seed morphology and the potential pool of consumers (Higgins et al 2003), with more recent studies continuing to emphasize seed recovery location as the only means of determining seed dispersal distances (e.g. Scott & Batchelor 2014). This approach provides limited understanding of rare long-distance dispersal events when compared with a contemporary vector-based approach that utilizes vector characteristics and behaviour to determine seed dispersal distances (Nathan et al 2008, Schurr et al 2009, Tsoar et al 2011.…”