NSW Bitou Bush Threat Abatement Plan - Department of ...

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Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera
River to Batemans Bay, areas free of bitou bush are interspersed with heavy infestations. South of
Batemans Bay, bitou bush only occurs in isolated disjunct infestations. The survey undertaken in
2000 (see Thomas and Leys 2002) estimated that more than 36,000 ha of private and public land
in New South Wales were infested with bitou bush. Of this area 6,700 ha was heavily infested
(bitou bush dominant), 9,000 ha was infested at a medium level (bitou bush present but not
dominant) and 20,100 ha had light infestations (scattered plants). In addition, the survey recorded
bitou bush up to 10 km inland. A map of the density of bitou bush in New South Wales is
presented in Appendix 11.
3.2.2 Arrival and spread of boneseed in Australia
The exact date and manner of arrival of boneseed to Australia is unknown. The first known record
is from a Sydney garden in 1856. The first known locations elsewhere in Australia include
Melbourne 1858, Adelaide 1892, Ulverstone (Tasmania) 1931 and Perth 1948 (Weiss et al. 1998).
Since its introduction, boneseed has been cultivated widely in most states. The majority of the
present day infestations can be attributed to escapes from gardens and nurseries (Adair and
Ainsworth 2000). Today, boneseed is widespread in South Australia (Mt Lofty Ranges), Victoria
(e.g. the Mornington Peninsula, the You Yangs, Ottways NP, Dandenong Ranges NP and near
Wimmera) and Tasmania (parts of the East Coast), with historic infestations in Western Australia
near Perth, the status of which is unclear. In New South Wales, boneseed occurs in coastal areas
from the Hunter River southwards, as well as in south-west New South Wales (e.g. Dareton).
Additional scattered infestations occur on the Central Coast, where it usually grows together with
bitou bush in non-dunal areas, and in the Sydney Metropolitan Area, where dense infestations are
found on clay soils along railway corridors.
3.2.3 Invasion by bitou bush and boneseed
Bitou bush and boneseed possess a range of attributes that contribute to their invasiveness and
ability to compete: rapid growth (including seedlings), a range of growth forms (bitou bush: shrub
or creeper), the capacity to grow in a wide variety of habitats, high fecundity, various vectors for
seed dispersal (particularly vertebrates) and seed dormancy. These attributes do not always result
in invasion or species dominance however.
Some native species have the ability to persist despite bitou bush’s vigorous growth rate and
dominance. For example, bitou bush has higher seedling vigour and greater survival at each life
stage than the native shrub coastal wattle (Acacia longifolia subsp. sophorae) (Weiss et al. 1998;
Vranjic et al. 2000), which nonetheless persists in bitou bush infested areas.
Bitou bush and boneseed, like many invaders, have an increased capacity to invade due to the
absence of their natural predators. Over the past 20 years six biological control agents have been
released on bitou bush, four of which have established, and six agents for boneseed, none of
which have established (see Downey et al. submitted). The lack of natural predators, and
deliberate plantings to stabilise sand dunes and remediate sand mining sites, has increased the
dominance and spread of bitou bush in Australia.