Advice to the Minister for the Environment, Heritage and the Arts from the Threatened Species Scientific Committee (the Committee) on Amendments to the List
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Summary of assessment: The Blue Gum High Forest is restricted to small bushland remnants nestled amongst the northern suburbs of Sydney which constitute less than 5 percent of the original forest area. The fragmented state of the ecological community makes it highly susceptible to invasion by weed species, many of which are escaped garden plants. Invasive species such as Camphor Laurel, Lantana, Privet, Ochna and Blackberry which occur in at least 50 percent of remnant areas have replaced the native woody component, altering the native floristic structure and composition of the ecological community and also degrading habitat for a range of native bird and mammal species. Existing remnants of the Blue Gum High Forest continue to be threatened by weed invasion. The Committee judges that this threatening process is adversely affecting the Blue Gum High Forest of the Sydney Basin Bioregion.Littoral Rainforest and Coastal Vine Thickets of Eastern Australia The Littoral Rainforest and Coastal Vine Thickets of Eastern Australia (‘Littoral Rainforest’) is currently listed as a critically endangered ecological community under the EPBC Act. As its name suggests, the ecological community represents a complex of rainforest and coastal vine thickets on the east coast of Australia. Typically, the ecological community occurs within two kilometres of the coast or adjacent to a large salt water body, such as an estuary and, thus, is influenced by the sea. The structure of the ecological community is typically a closed canopy of trees that can be interspersed with canopy gaps that are common in exposed situations or with storm events. The Littoral Rainforest contains a range of plant life forms including trees, shrubs, vines, herbs, ferns and epiphytes (TSSC, 2008). The Littoral Rainforest, originally an almost continuous archipelago of patches along the eastern coast of Australia, has undergone a reduction in extent and fragmentation primarily as a result of coastal development, sandmining and agriculture (Bradley and Merrilyn, 1992). This fragmentation and reduction in patch size have increased the ecological community’s vulnerability to other threats including invasion of escaped garden plants. Whether the ecological community is protected in reserves or not, the risk of escaped garden plant invasion increases where patches of the ecological community are located near human habitation and/or are subject to visitor disturbance (TSSC, 2008). A study by Peel (in prep.) found that the majority of weeds recorded were incidentally introduced through human activities, including domestic gardens and associated refuse dumping. Escaped garden plants that invade littoral rainforest, notably Lantana, Bitou Bush and Rubber Vine, are now recognised as Weeds of National Significance (WoNS). The establishment of transformer weeds, many of which are escaped garden plants, in littoral rainforest patches can have a significantly detrimental effect (TSSC, 2008). Transformer weeds are highly invasive taxa with the potential to seriously alter the structure and function of the ecological community. Whilst it is accepted that the ecological community can tolerate a significant amount of weed cover due to its relative resilience, if left unchecked, such weeds will eventually take over and destroy the affected patch (TSSC, 2008). Peel (in prep.) observed the impact of escaped garden plants in 2002-03 in the Marlo Estuary, Victoria, where weed invasion alone (i.e. without any other disturbance) had destroyed a third of the littoral rainforest stand and left the remaining two thirds in a state of severe decline. The escaped garden plant species that caused this degradation included Blue Periwinkle (Vinca major), Cape Ivy (Delairea odorata) and Wandering Jew (Tradescantia albiflora). Peel (in prep.) concluded that the ecological community, in this area, could disappear in the next five to ten years without proper intervention. Given the aggressive nature of transformer weeds, it can generally be deduced that seriously infested patches of the ecological community will be lost in the short to medium term in the absence of effective control of escaped garden plants (TSSC, 2008). In New South Wales, many coastal habitats, including Littoral Rainforest, have been invaded by Bitou Bush which can smother canopy species and may form dense growth around the edge of the ecological community (Adam, 1992). The NSW Threat Abatement Plan for Bitou Bush recognises that this escaped garden plant poses a serious threat to littoral rainforest in northern NSW by invading the rainforest margins and canopy gaps, thereby disrupting recruitment processes (NSW DEC, 2006). In northern New South Wales, remnant stands of the ecological community have been invaded by escaped garden plants such as Cat’s Claw Vine (Macfadyena unguis-cati) and Madeira Vine (Anredera cordifolia) (Adam, 1992). Along the eastern coastline, Asparagus Fern (Asparagus aethiopicus) and Lantana are well established in many patches of the ecological community where they pose a serious threat to littoral rainforest species through their habit of climbing and smothering (TSSC, 2008). Not only are established trees killed by these weeds, but germination and recruitment of seedlings are severely hindered if not inhibited (Bradley and Merrilyn, 1992). The presence of various escaped garden plants typically of the warm temperate climate zone of south-eastern Australia, such as Cape Ivy, Bitou Bush, Lantana and Madeira Vine, in the sub-tropical zone of northern NSW (Williams, 1993; Peel, in prep) demonstrates that certain escaped garden plants have the capacity to significantly expand their range on the eastern coastline to the detriment of the Littoral Rainforest ecological community. Summary of assessment: The Littoral Rainforest ecological community has undergone a reduction in extent and fragmentation primarily as a result of coastal development, sandmining and agriculture. This fragmentation and reduction in patch size have increased the ecological community’s vulnerability to other threats including invasion of escaped garden plants (TSSC, 2008). Invasive garden plant species such as Lantana, Bitou Bush, Rubber Vine, Blue Periwinkle, Cape Ivy, Wandering Jew, Cat’s Claw Vine and Madeira Vine compete with native vegetation, altering the native floristic structure and composition of the ecological community. Existing remnants of the Littoral Rainforest are likely to continue to be threatened by escaped garden plants as these invasive species expand their range on the eastern coastline (TSSC, 2008). The Committee judges that this threatening process is adversely affecting the Littoral Rainforest and Vine Thickets of Eastern Australia. |