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

Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera
5 The impact of bitou bush and boneseed invasions on
fauna
In the past, studies on the effect of plant invasions on fauna have received little attention (French
and Eardley 1997; Adair and Groves 1998). However, recent studies involving a range of weed
species have highlighted the diverse ways in which birds and mammals (Lawrie 2002),
invertebrates (French and Eardley 1997), reptiles (Hoefer pers. comm.) and amphibians
(Wellington pers. comm.) interact with weeds. Some interactions have negative effects on fauna.
For example, Spartina invasions can convert tidal mudflats into grasslands, resulting in the loss of
habitat for many wading birds (see Lane 1992). Some interactions have positive effects on fauna.
For example, introduced plants with spines or thorns can provide protection to rare mammals like
the southern brown bandicoot (see Regel et al. 1996). Such weed–fauna interactions can also
affect groups of species in different ways. For example, bird species were both negatively (8
species) and positively (10 species) affected following Scotch broom invasion (see Bell 1990).
Weeds affect fauna in different ways: altering food resources, feeding substrate, nesting/breeding
sites, shelter and protection from predators, roosting and perching sites, and movement corridors.
An audit system has been proposed by Lawrie (2002) based on observations of animals (or animal
signs such as scats) within infested areas, to determine weed–fauna interactions. In Australia 225
bird species have been recorded interacting with 482 introduced plant species, and 43 mammals
interacting with 55 introduced plant species (Lawrie 2002). The information obtained by this audit
system does not provide a complete picture however, as it is biased towards positive interactions.
For example, declines in fauna density are unlikely to be recorded without rigorous studies. In
addition, the proposed audit system does not provide detailed information on the exact nature of
effects on fauna and detailed studies are needed in some areas to provide information in addition
to that obtained from the proposed audit system.
The removal of weeds from sites that have been infested for many years may affect fauna that
have modified their lives as a result of these infestations. For example, the removal of
blackberries in Belair National Park, South Australia may lead to a decline in the threatened
southern brown bandicoot, as blackberries provide protection from predators (see Regel et al.
1996). Blackberry removal programs therefore need to consider the introduction of replacement
measures to protect these threatened bandicoots. Historically, such impacts have rarely been
considered in weed control programs.
Information on the interactions between weeds and fauna, both positive and negative, needs to be
collected and incorporated into weed management strategies (Lawrie 2002). Information on the
effect on fauna of controlling weeds also needs to be collected and incorporated into such
strategies.
5.1 Interactions between bitou bush and vertebrates (birds and
mammals)
Information on the impact of bitou bush invasion (and its control programs) on vertebrates (native
or introduced) is limited. Dodkin and Gilmore (1984) highlighted the need to collect information
on the impacts of bitou bush on fauna, however, only a handful of studies have been published
since. The impact of bitou bush invasion on fauna was acknowledged by the NSW Scientific
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