The threat posed by weeds is ranked as the second greatest cause of biodiversity decline after habitat loss. It is estimated that there are approximately 2,800 weed species in Australia, with 71 recognised as Weeds of National Significance (WONS).¹  Eight of the top 20 WONS species are present on the Central Coast. These include Blackberry, Lantana, Bitou Bush, Salvinia, Willows, Gorse, Bridal Creeper and Alligator Weed.

The Central Coast area is located within a high rainfall area (approximately 1000mm – 1200mm pa) with a diverse range of soils and plant communities. This feature along with disturbances related to agriculture, forestry and urban development along with vegetation disturbance for roads, railways, powerlines, pipelines and other infrastructure developments has created areas where weed species establish and thrive.

Excessive weed invasions in some habitats can result in significant changes to the vegetation structure and plant species composition to the extent that the native fauna diversity is adversely affected. It is at this stage that weed invasions can become a real environmental, ecological and economical problem.

Care must be taken in controlling or removing weeds as they may have become habitat, shelter or a food source for many native animals and using herbicide may be problematic as they may effect some species, such as frogs.

Key Threatening Processes

Key threatening processes are the things that threaten - or could threaten - the survival or evolutionary development of species, populations or ecological communities. Key Threatening Processes relating to weeds that are listed under Schedule 3 of the Threatened Species Conservation Act, 1995 include:

• Invasion and establishment of Exotic Vines and Scramblers (eg. Morning Glory, Bridal Creeper).
• Invasion of native plant communities by Bitou Bush (Chrysanthemoides monilifera ) and boneseed.
  
• Invasion of native plant communities by exotic perennial grasses (eg. Kikuyu Grass, Rhodes Grass, African Lovegrass, Vasey Grass, Paspalum).
• Invasion, establishment and spread of Lantana camara.

• Invasion and establishment of Scotch Broom (Cytisus scoparius).

What are Weeds?

• Weeds are often introduced species, but they can also be native species growing outside their natural range (non-endemic).²
• Weeds are often problem plants, they are usually plants that seed and fruit prolifically and can rapidly invade natural areas.
• Weeds occur in both terrestrial and aquatic ecosystems.
• Ecosystems in southern Australia are generally subject to multi-species invasion, at a local scale a single species may dominate but in general no one species will dominate an entire area.³

Weed Significance

Weeds can be assessed on a variety of levels:

• Weeds of National Significance represent the most serious weed problems in Australia and are determined by four criteria: Invasiveness; Impacts; Potential for Spread; Socio-economic and environmental values.

• Noxious weeds are weeds listed under the Noxious Weeds Act, 1993.
• Local Weeds include weeds that are listed on Local Government weed policies.

Weed Facts

• In Australia; Approximately 70% weeds are garden escapees.⁴ It costs farmers $4 billion annually in weed control costs and lost production.⁴
• In NSW; In 2005-06 the Department of Environment and Climate Change spent $18 million in weed and animal control in National Parks.⁴
• On the Central Coast; It is estimated that volunteers contribute about $4 million annually to the control of weeds in bushland reserves.

Impacts of Threat

Invasion of weed species has a negative impact on biodiversity and ecological communities. Some of the threats of weed infestation include:

• Reduced natural species diversity as a result of direct competition and disruption of essential ecosystem processes.⁵
• Disruption and displacement of local fauna through loss of habitat.
• Reduction in genetic diversity by reducing the genetic base of a population at a local, regional and national scale.⁵
• Competition with native species for nutrients, space, pollinators, sunlight and water.²
• Suffocation of native plants, prevent regeneration and changes the structure and function of an ecosystem.²
• Degradation of the aesthetic, social and environmental value of natural areas.
• It provides areas that harbor pest animals, diseases and pathogens.

The Local Problem

• Increased nutrient runoff and changes to soil moisture and content in bushland areas are significant factors causing an increase in weed invasion.
• The following weeds are considered to be the Weeds of Regional Significance for the Central Coast region: Blackberry, Crofton Weed, Alligator Weed, Lantana, Salvinia, Water Hyacinth, Bitou Bush, Green Cestrum, Morning Glory, Privet, Pampass Grass, Giant Parramatta Grass, Mother of Millions, Camphor Laurel, Bridal Creeper and Madeira Vine.

Management Issues

• Biological Control agents have been released for Alligator Weed, Bitou Bush, Bridal Creeper, Lantana, Salvinia, Prickly Pear, Noogoora Burr, and Water Hyacinth with varying success.
• Bushcare, Landcare and Dunecare groups have been instrumental in controlling many weeds.
• Education programs for Nurseries and the community to promote suitable natives or alternative plants for gardens.
• Councils have an active program in place that manages the control of noxious weeds on land under the care and control of Council.
• Councils also have an inspection program for private property that includes the enforcement of the Noxious Weeds Act.

Community Actions

• Become familiar with identifying weed species.

• Remove weed species from your garden and control weeds on your land (eg. Lantana, Privet).

• Consider the possibility of exotic garden species becoming weeds in the nearby bushland.  Remove species that have this possibility, or alternatively remove seed heads, spent flower heads or fruit.

• Plant locally occurring native (endemic) species, consult your local nursery for more information.

• Do not dump garden waste.

• Become a member of your local environment group and get involved in local activities.

• Participate in rehabilitation programs with your local Landcare, Bushcare or Dunecare group.

• Improve your skills, knowledge and understanding of native vegetation.

Useful Web Links

• Department of Environment and Water Resources - www.environment.gov.au
• Department of Environment and Conservation Native Plant Schemes - ‘Garden Plants under the Spotlight’, ‘Flora and Fauna Program’, ‘Australian Plants Society’ & ‘Bushland Friendly Nursery’ www.environment.nsw.gov.au
• NSW Weed Strategy - www.agric.nsw.gov.au

• Weeds Factsheet Information - www.weeds.crc.org.au
• ‘Friends of Strickland” Community Group - www.forest.nsw.gov.au

Further Reading

• Local noxious weed lists are available from your Local Council.
• Loughran, A. 2006, Native Plant or Weed? Pick the Difference, NSW Department of Primary Industries.
• Richardson, F.J., Richardson, R.G. and Shepherd, R.C.H. 2006, Weeds of the South-East - and identification guide for Australia, R.G and F.J. Richardson.  

Bibliography

1. Coutts-Smith, A.J. and Downey, P.O. 2006. Impact of weeds on threatened biodiversity in New South Wales. Technical Series No.11, CRC for Australian Weed Management, Adelaide.
2. Department of Environment and Conservation (updated 20 December 2004), ‘Weeds’. Retrieved 8 September 2006 from http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Weeds.
3. Adair, R.J. and Groves, A.H. 1998, National Weeds Program: Impact of Environmental Weeds on Biodiversity, Environment Australia, Canberra.
4. Parliamentary question by Mr Ian Cohen March 2006, answered May 2006 http://parliament.nsw.gov.au/prod/lc/qalc.nsf/0/0EA53638858C302ECA25713F00283445.
5. Muyt, A. 2001, ‘Bush Invaders of South-East Australia , R.G. & F.J. Richardson, Meredith, Victoria.