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Plants which have an adverse affect on human health, the environment, livestock on agriculture can be declared a noxious weed. The NSW Noxious Weeds Act 1993 requires the control or removal of plants declared noxious weeds.
Like the Cane Toad some noxious weeds, have been deliberately introduced as Garden Plants, agricultural crops and animal fodder and then turn out to be better adapted to high levels of nutrients, storm water runnoff and free of predators.
As these plants take over from the local provenance vegetation, native animals which relied on the local species loose their source of food and habitat. The local provenance plants, may have also relied on these butterflies and insects for cross polinatation.
Sticky or Asthma weed a native of the mediterranean arrived as seeds in clay clinging to Italian marble which was made into fireplace surrounds -Parietaria Judaica. In the dry exposed climate of Malta and the Mediterranean the sticky stems help the plant cling to rocks and it provides food source and habitat to the Red Admiral (Vanessa atalanta) Butterfly for example. However, in Sydney, with more sunlight, more water, ideal nutrients, wind and animal dispertion, no predators it is a noxius weed.
Fruit and Seeds from Garden plants can be carried by the wind or birds into the bush or neigbouring gardens and become environmental weeds.
Plants that can be seen in Sydney Bushland and which spring up in gardens uninvited include:
Australian Native species such as the Cootamundra Wattle have also become weeds, when relocated to other parts of Australia. While West Australian natives adapted to dry sandy alkaline conditions often do not do well in Sydney.
Long cultivated Camphor Laurel (provides Camphor Oil and Timber) and Mulberry Trees (food for silkworms) untended have become weeds and damage the ecosystem, in Australia. Australian Eucalypts and Accacias have also become problematic elsewhere in the world where they were used for reforestration projects. As well as providing habitat and food, plants also affect they draw on nutrients, affect the soil, water table, create microclimates.
There are a wide range of plants that are native to the Sydney Area. The Rozelle Bay Community Native Nursery in Annandale, propagates plants from nearby bushland and has successfully reintroduced a wide range of Local Provenance Plant Species to Inner Sydney - which has attracted a wide range of native birds and Butterfles.
Native Bees can be seen buzzing around the blue flowers of Commelina Cyanea but not the similar looking, noxious weed Tradescantia fluminesis, which has white flowers). Commelina is a native of NSW and Queensland and Tradescantia is a native of South America. Commelina is a self sowing annual, whereas the heavier Tradescantia can be seen all year round.
The Sydney Weeds committee has created a pamphlet to encourage gardeners and nurseries to choose and stock alternatives to plants that have become weeds in Australia. For alternatives see Nursery Industry Garden Escapes Project - "Grow Me Instead!"
www.ramin.com.au/eco-sydney/camphor-laurel-and-other-weeds.shtml © Ramin Communications 2009-2010. Last modified 7 June 2011.