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Weeds
A weed is any plant growing where it is not wanted. Weeds tend to spread easily and grow rapidly therefore choking out native vegetation. Plants may be weeds in one place but a useful plant in another.
Weed invasion is a major issue for many of the remaining stands of bushland in the Blacktown area.
The spread of weeds
Weeds spread when a propogule (such things as seeds, cuttings, tubers) are carried into an area where they can then grow.
Weeds are spread by various means:
- Dumping of garden waste
- Stormwater washing propogules into local creeks
- Animals which carry barbed or sticky seeds in their fur or feathers, eg Cobbler's Pegs
- Animals eating plants and then defeacating the seeds
- Wind which can blow feathery or wing shaped seeds, eg Dandelion
The pronged seeds of Cobblers Pegs (Bidens pilosa) are very good at attaching themselves to passing animals. |
Dandelions are a good example of a weed that utilises wind to spread its seeds. |
Why weeds take hold
Weeds, by their very nature, colonise an area very quickly, usually at the expense of the native vegetation. In significantly sized stands of undisturbed native bushland, it is very hard for weeds to take hold, as the native vegetation is well adapted and thriving in the prevailing conditions. It is in the disturbed areas where the weeds have the advantage as natives are slow at colonising.
In urban areas where isolated pockets of bushland rather than large stands are the norm, it is much easier for weeds to invade and it is along the edges of remnant bushland where habitat disturbance is greatest.
Factors such as those listed below significantly increase the spread and colonisation of weeds.
- increased light
- excess water runoff
- nearby roads leading to increased chemical interference from soot, car exhaust
- easier access for dumpers
- increased nutrients from mown grass or tree felling
Another disturbance associated with the urban environment that promotes weed invasion is stormwater drainage into local creeks. Stormwater run off from car parks, roads, open spaces, playing fields and gardens means that creeks which once were seasonal now flow all year round and the water they carry is rich in nutrients. These conditions encourage the growth of exotic species which are more suited to high water and nutrient conditions than are Australian native plants.
