In simple terms, a weed is a plant growing where it is not wanted.

Both introduced and native plants have the potential to become weeds, if they have certain 'invasive' characteristics including:

  • the production of large numbers of viable seeds which may remain dormant in the soil for a number of years
  • effective dispersal mechanisms such as spikes, hooks and wings, or fruit that attracts animals
  • rapid establishment and growth of seedling, which allows them to out-compete other plants
  • the ability to reproduce and regenerate vegetatively
  • the ability to invade recently disturbed lands such as road verges and gravel pits
  • the ability to release self-protecting toxins that interfere with the growth of surrounding plants (allelopathic).

Common terms used to describe weeds

Declared plant
A weed that has been ‘Declared’ under the Biosecurity and Agriculture Management Act 2007 and Biosecurity and Agriculture Management Regulations 2013. Use the Western Australian Organism List to search for declared plants within a particular region of Western Australia and contains information on the status of a plant, its declaration, a brief description and control methods.
Environmental weed
An introduced plant that establishes in natural ecosystems and adversely modifies natural processes, resulting in decline of invaded communities.
A plant occurring in a place where it is not native.
Invasive plant
One that is introduced and successfully reproduces resulting in the establishment of a population that spreads and threatens ecosystems, habitats or species with economic or environmental harm. Not all introduced species are invasive if there are controls on their spread or competitiveness.
Naturalised plant
A plant that is not native to an area but has become established and can reproduce there. Not all naturalised species become weeds or have detrimental environmental or economic effects, but many do.
A plant that requires some form of action to reduce its harmful effects on the economy, the environment, human health and amenity (Australian Weeds Committee 2006), and can include plants from other countries, or other regions in Australia or Western Australia.

Why are weeds a problem?

Weeds, along with other invasive species, now pose one of the most significant threats to biodiversity (Australian Weeds Strategy).

Weeds can have a significant impact on natural values by:

  • successfully out-competing native species for available nutrients, water, space and sunlight
  • reducing the natural diversity by smothering native plants or preventing them from growing back after clearing, fire or other disturbance
  • replacing the native plants that animals use for shelter, food and nesting
  • altering fire regimes, often making fires hotter and more destructive.