Weeds

Content: What is a weed? | Noxious weeds | Environmental weeds | Weeds are a problem because: | Weed control

What is a weed?

A weed, generally speaking, is a plant growing where it is not wanted or growing out of place. A few terms are used when defining weeds.These include:

• ‘naturalised’ - a plant introduced into a region that is flourishing as if it were native to the area;
• ‘exotic’ - a plant foreign to an area (may be a native to another part of the same country) but not fully naturalised;
• ‘introduced’ - a plant not present in the area before European settlement.

Weeds often have one or more of the following characteristics that allow them to flourish in urban bushland:

• the lack of natural predators and diseases (left behind in the country of origin);
• rapid seedling growth and high seed output;
• produces seed after only short period of vegetative growth;
• high tolerance to climatic and soil variation;
• vigorous vegetative reproduction;
• a lack of special environmental requirements for germination.

Noxious weeds are plants which, if left uncontrolled, will spread widely and cause serious economic loss to agriculture or have some detrimental effect upon humans, animals, the environment or community in general. Provided there is a reasonable and enforceable means of control, such plants are candidates for declaration as noxious plants. They are usually hard to eradicate, spread rapidly and may have toxic properties.

Environmental weeds are plants that pose a threat to bushland reserves but have not been declared noxious by the Department of Agriculture. There is no legal responsibility to eradicate these weeds, but it is recommended that they be controlled to prevent degradation of our remaining bushland. They include many popular garden plants, eg Privet, Asparagus Fern and Honeysuckle. The local weed list includes the main weeds found in the Illawarra region and it is constantly being revised as new weeds appear on the scene or as non-invasive weeds become naturalised and become a problem.

Weeds pose a great threat to bushland in the urbanised Wollongong City area. Weeds flourish in gardens and other areas where the native vegetation cover is disrupted. Broad scale urban development leads to disturbed soil, increased nutrient levels in water ways, altered fire regimes, increased volumes of refuse and removal of large areas of native bushland. This has created the ideal conditions for environmental weeds to colonise and flourish in much of the Illawarra’s remnant bushland, and with four-to-six new weeds entering Australia each year this situation is continually exacerbated.

Weeds a problem because:

• their invasion may bring about irreversible changes in the structure, composition and ecology of naturally occurring communities;
• they compete with native species for water, nutrients, light and space. This may ultimately reduce the population size and alter the species composition of the native vegetation;
• they repress the juveniles of canopy species which leads to the eventual elimination of native canopy species, replaced by a weed understorey;
• they bring about unavoidable changes in the natural fire regime because of different flammability and responses to fire itself, which results in changes in the types of native plant present;
• they enrich the soil by adding nutrient-rich leaf litter, resulting in a permanently enriched soil profile;
• their presence leads to a decrease in species diversity creating an unattractive environment, with a subsequent devaluation of the area and a consequent decrease in conservation values for the bushland;
• they create a change in available food sources and habitat value for wildlife with a consequent shift in faunal populations.

Weed control
Weeds are really a symptom of an underlying cause or impact. It is important to address the impact where possible in addition to removing weeds. There are a number of different weed removal techniques that can be applied in urban situations. These hand removal techniques may, in some cases, be supported by carefully introduced biological controls.

In many cases natural bushland is dependent on natural disturbances such as fire, flood and high winds for regeneration to take place. If these disturbances are too frequent or are ongoing they can have a detrimental effect on natural bushland and encourage the growth of weeds. The greater the degree of disturbance the greater the degree of weed invasion.