What is a weed?
Working as a bush regenerator I have often pondered this question. There seem to be many definitions of a weed. The common definition which is thrown around a lot that ‘a weed is any plant out of place’ is probably a simplified definition. It is also subjective. What may be a well-liked plant in someone’s garden, could be a detrimental environmental or agricultural weed.
The Macquarie Dictionary defines a weed as ‘a plant growing wild, especially in cultivated ground to the exclusion or injury of the desired crop’ or ‘any useless, troublesome, or noxious plants, especially one that grows profusely’. This is getting a little closer.
The Australian Association of Bush Regenerators (AABR) defines a weed as ‘any plant that colonises and persists in an ecosystem in which it did not previously exist. They may affect the economy, the environment, human health and amenity’.
The Biosecurity Act 2015 NSW defines a weed as ‘a plant that is a pest’. It then goes on to define a pest as ‘a plant or animal (other than a human) that has an adverse effect on, or is suspected of having an adverse effect on, the environment, the economy or the community’.
These last two definitions by AABR and the Biosecurity Act are quite good. They both take into account the effect of weeds on bushland areas, agriculture and the economy. Therefore, it appears land use has a lot to do with the definition of a weed. On a farm a weed could be quite different to what a weed is in the bush or in a residential garden.
Local councils define weeds as differing priority levels according to their regional plan. This includes listing plants as prohibited matter as listed under the Biosecurity Act. Prohibited matter refers to weeds that are banned from entering or being in the state because they pose a high risk to the economy, environment, or community. Examples include Gamba grass, Mexican feather grass, and Parthenium weed.
Categorising weeds is useful from a management point of view. It identifies weeds which are new incursions into an area or ones that can cause the most harm. From a management point of view this does make sense. It means you can tackle new or harmful weeds before they become a problem. From a habitat perspective, a weed is a weed. It matters not to native animals what the category of a weed is. They just need them gone.
Another definition of a weed is a plant that is not endemic to a particular area. For example, the Cootamundra wattle (Acacia baileyana) which occurs naturally within a narrow range surrounding the town of Cootamundra. However, outside this range it spreads quite rapidly and has become a problem in some areas.
This begs the question, which is the correct definition? Perhaps taking into account the context of the site. Whether is it agricultural land, native bushland or residential garden. Also, the actual location seems important as seem plants are weeds in one region but not in others.
