• A plant out of place (environmental weed that may be either exotic or native).
  
• A pest plant.
  
• A plant where local natural control methods have not developed.

• Animal fodder
• Ornamental gardens
• Ornamental parks and forestry planting
• Inappropriate disposal of garden waste
• Clearing of land for farming activity
• Plants used to prevent erosion or wind breaks etc
• Dispersal of seeds – wind, water, birds, animals, humans, machinery
• Spread underground – new shoots, bulbs, tubers, rhizomes
• Self pollination

Weeds are extremely opportunistic. Disturbances to natural habitats by human activities such as clearing for farming, animal grazing, forestry, urbanisation and introduction of feral animals such as hares result in rapid colonisation of weeds. Weeds thrive for example where fertilizers, dumping of garden refuse, organic wastes, etc are washed into bushland due to the extra nutrients they contribute to the soil.

• Reduce the survival of native plants and animals.
  
• Choke waterways such as creeks, wetlands and flood plains.
  
• Degrade water quality.
  
• Compete with native vegetation for sunlight, space and nutrients.
  
• Decrease biodiversity.
  
• Decrease food, shelter and natural habitat for native fauna.

Weeds Australia: www.epa.gov.au/biodiversity/invasion/weeds.html
Greening Australia: www.qld.greeningaustralia.org.au/weedguide

NRM Factsheets:
The Department of Natural Resources and Mines has on its website information sheets for individual environmental weeds and the Environmental Weeds list ( 200 most invasive environmental weeds in SEQ) www.nrm.qld.gov.au/factsheet