Causes of Weed Invasion

Our Blue Mountains townships and villages perch on the ridges above some of the most biologically diverse, fragile and beautiful natural vegetation in the world.

We people have dramatically altered our natural environment, and all human activities carried out in our townships affect our downslope bushland, our National Park, and our streams and rivers.

Urban Runoff:       Off the Garden, into the Bush

Stormwater rushes off all our hard surfaces - roads, roofs, car parks, garages, factories and driveways - carrying with it the pollutants and detritus of everyday life. These include oils and chemicals, rubbish and organic litter, soil from cleared land, fertilisers, pesticides, herbicides, sewage from overflows, weed seeds and animal faeces.

This fast-flowing stormwater cocktail enters the bush, erodes the watercourses, silts the creeks, and changes the nature of the soil. Many of the components of this urban runoff increase the nutrient levels in the soil. Most of our native plants are adapted to low nutrient conditions: they fail to thrive, they may die. But this moist, fertile soil favours the growth of weeds, and invasive species such as Montbretia, Blackberry and Privet soon move in.

Silt-laden stormwater carries weeds into the bush.

Bush Invaders:       Out of the Garden - Into the Bush

Many ornamental plants have escaped from our parks and gardens to become bush invaders.

Some spread their seed on the wind, some rely on water, some eject their seed explosively. Some use us, or birds, or other animals, machinery or soil to move their seeds about, some spread vigorously without the use of seeds at all. Many plants use more than one of these distribution methods.

Weedy plants have certain characteristics in common, including few enemies, fast growth, the ability to grow almost anywhere, and the ability to reproduce and spread rapidly.

All of the weeds on this web site are aggressive competitors with our unique native plant species. Weeds destroy the habitat of our unique indigenous fauna.

Dumping:       Over the Fence, Into the Bush

 Cartoon: dumping weeds over fence

"Not in my backyard!"

Norman Yeend

Some people introduce weeds into bushland by deliberately dumping garden prunings, grass cuttings, leaf litter or soil.

Dumped plants, rakings and clippings quickly grow and invade the bush. Dumped soil introduces weed seeds, buries native plants and their seeds, and compacts the soil.

Disturbance:       Out of the Suburbs, Into the Bush

Why are weeds so prolific along roadsides, bushland edges, along watercourses and tracks?

The cause is human activity again: any kind of disturbance of the original soil conditions leads to weed invasion. Disturbance such as clearing, excavating, slashing, mowing or burning creates opportunities for weed invasion.

The disturbance of driving, riding, parking and walking on bushland vegetation causes erosion and compaction of soil, and introduces weed seeds.

Bush Cancer:       What's Wrong with Weeds?

Weeds are plants free of their natural predators which thrive in changed bushland conditions.

They compete vigorously with our native plant species and frequently dominate and replace them. They degrade and destroy the habitat of our native fauna. They restrict animal and human access to tracks, creeks and waterholes. They reduce local biodiversity, and they permanently change ecosystems.

 Morning Glory dominating native plants

Weeds like Morning Glory
dominate and replace
native plants

Like many cancers, in the early stages the invasion is slow and insidious, but once recognised weeds can be cut out and the bush can recover. If we leave it too long, however, weeds will destroy our bush.

We can help by ...

Free booklet - Weeds of Blue Mountains Bushland

Have a copy of this free booklet posted to you by telephoning Council’s Bushcare Section on
4780 5528
download it now
as a PDF file.
request online
for a copy to be posted.

  • learning to recognise weeds with the free booklet Weeds of Blue Mountains Bushland on which this web site is based
  • understanding how and why weeds spread
  • removing bush-invading plants from our gardens
  • choosing only bush-friendly garden species
  • composting and mulching green waste
  • disposing of other waste at the tip
  • keeping our gardens within their boundaries
  • retaining car wash and garden water on our blocks
  • choosing to use phosphorous-free detergents
  • using only organic slow-release fertilisers
  • mulching to improve water absorption and retention
  • keeping garden wastes out of the road gutters
  • picking up pet wastes and disposing of them responsibly
  • always keeping to authorised bushland tracks
  • encouraging our friends and neighbours to follow these principles
  • and joining a local Bushcare group

Bushcare groups:

The challenge for us all as we become increasingly urbanised is to develop sustainable lifestyle patterns that will enable us to live in harmony with our bushland.