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Weed invasion

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

Causes of weed invasion

Many of our suburbs and towns adjoin some of the most biologically diverse, fragile and beautiful natural vegetation in the world. What we do in our gardens and public spaces has dramatically altered our natural environment. In particular, activities in built-up areas affect our downslope bushland, our National Parks, and our creeks 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, insecticides, herbicides, sewage from overflows, weed seeds and animal faeces.

This fast-flowing stormwater cocktail enters the bush, erodes the watercourses, silts up 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. But this moist, fertile soil favours the growth of weeds, and invasive species such as montbretia, blackberry and privet soon move in.

Montbretia invading a gully affected by urban runoff.

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 seeds on the wind, some rely on water, some eject their seeds explosively. Some use us – or birds or other animals –, machinery or soil to transport their seeds; 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.

Many weed species compete aggressively with our unique native plant species and destroy the habitat.

Dumping: over the fence, into the bush

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, watercourses and tracks?

The cause is human activity again: any kind of disturbance to 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 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.

Weeds like morning glory dominate, smothering and replacing native plants. Photo: Jeanette Nobes.

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 ...

• learning to recognise weeds in bushland and parks
• 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 land
• choosing to use phosphorus-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
• joining a local Bushcare group.

This article is taken from the Weeds of Blue Mountains Bushland web site (http://www.weedsbluemountains.org.au/) in accordance with the conditions of use.