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

Abstract

Citation: Scott JK, Batchelor KL, Webber BL (2019) Long term monitoring of recruitment dynamics determines eradication feasibility for an introduced coastal weed. NeoBiota 50: 31-53. https://doi. AbstractBitou bush (Chrysanthemoides monilifera subsp. rotundata) is a Weed of National Significance in Australia and has impacted a significant portion of the eastern coastline. Its discovery in Western Australia was, therefore, a cause for concern. Assessment and control of the isolated and well-defined population began in 2012. To assess the feasibility of eradication in Western Australia as a management outcome for bitou bush, we applied a rigorous data-driven quantification and prediction process to the control program. Between 2012 and 2018 we surveyed over 253 ha of land and removed 1766 bitou bush plants. Approximately 97 person-days were spent over the six years of survey. We measured the seed bank viability for five years starting in 2013, with the 2017 survey results indicating a decline of mean viable seeds/m 2 from 39.3 ± 11.4 to 5.7 ± 2.2. In 2018 we found only ten plants and no newly recruited seedlings in the population. No spread to other areas has been recorded. Soil core studies indicate that the soil seed bank is unlikely to persist beyond eight years. Eradication of the population in Western Australia, defined as five years without plants being detected, therefore remains a realistic management goal. The information generated from the documentation of this eradication program provides invaluable insight for weed eradication attempts more generally: novel detection methods can be effective in making surveys more efficient, all survey methods are not entirely accurate and large plants can escape detection, bitou bush seeds persist in the soil but become effectively undetectable at low densities, and migration of seed was unquantifiable, possibly compromising delimitation. Continued monitoring of the Western Australian population will determine how much of a risk these factors represent to eradication as the outcome of this management program. John K. Scott et al. / NeoBiota 50: 31-53 (2019) 32 A peer-reviewed open-access journal NeoBiota

Genomics reveals the history of a complex plant invasion and improves the management of a biological invasion from the South African–Australian biotic exchange

“…Evidence from glasshouse experiments (Gross et al, 2017 ) and field observation (Scott, Batchelor, Jucker, & Webber, 2019 ) points to bitou bush being an obligate outcrossing taxon. Vegetative reproduction is rare (Scott, Batchelor, & Webber, 2019 ), but when it does occur, it is mainly from plants in mobile dunes or as a consequence of stem sections being covered by soil. The impact of bitou bush on ecosystems is via competitive displacement of native vegetation, production of allelopathic compounds, and alteration of soil biogeochemical cycling (Ens et al, 2009 ; Lindsay & French, 2004 ; Mason & French, 2008 ).…”

“…Regional extirpation is also being attempted at the southern limit of the range in Victoria, but this may be complicated by hybridization with boneseed (Adair & Butler, 2010 ). In Western Australia, eradication from the entire state is being attempted and may be more feasible, although the current management program still has years to run (Scott, Batchelor, & Webber, 2019 ).…”

“… (a) World map with, inserts for (b) southern Africa, (c) eastern Australia and (d) Western Australia (Kwinana Industrial Estate) showing distribution of bitou bush (based on records from GBIF for southern Africa and eastern Australia; and Scott, Batchelor, & Webber ( 2019 ) for Western Australia. Larger dots show sample locations of Chrysanthemoides monilifera used in this study (listed in Table S1 ).…”

“…Considerable effort has been spent on managing the worst of the exchanged weeds in both countries, including eradication attempts (e.g., Chrysanthemoides monilifera ssp. rotundata ; Scott, Batchelor, & Webber, 2019 ) and classical biological control programs (e.g., Asparagus asparagoides ; Morin et al, 2022 ). However, both countries have ecosystems spanning a wide range of climates and many of the most problematic weeds occupy a broad realized niche (e.g., Lycium ferrocissium ; McCulloch et al, 2020 ).…”

A weed risk analytical screen to assist in the prioritisation of an invasive flora for containment

“…Wilson et al (2017) provide a recent summary on the topic. The emerging conclusion is that eradication is feasible in a relatively small number of cases (Panetta 2015;Scott et al 2019;Williams et al 2019;Hulme 2020), owing largely to attributes that distinguish weeds from other invasive organisms, such as the potential for development of persistent seed banks. Difficulties in achieving eradication are generally more pronounced for weeds of natural, as opposed to highly modified ecosystems (Panetta and Timmins 2004;Panetta 2009;Moore et al 2011).…”