Contents

• What are Environmental Weeds?
• The Disaster of Prickly Pear
• The Victorian Catchment & Land Protection (CaLP) Act
• Noxious Weed Lists For Other States
• Other Environmental Weeds
• A Litany Of Horticultural Disasters
• The Cost of Environmental Weeds
• Sleeper Weeds
• Is there a place for exotic plants in our gardens?
• Alarming Report From Weeds CRC

What are Environmental Weeds?

            Indigenous plants are an integral part of the local ecosystem and there is a complex web of interactions between them, other indigenous plants, disease micro-organisms, mammals, birds and insects. As a result of the combined effects of these checks and balances long term take over bids by any one individual species is prevented.

            When you plant an exotic plant, or even an Australian native plant of distant origin, in that same ecosystem equivalent checks and balances on the species are very unlikely to be present. As a result it is possible for that species to mount a successful and prolonged take over bid of the ecosystem. 

            Environmental weeds behave in a very similar manor to human cancer cells so it is also appropriate to describe them as environmental cancer.

            As the environmental weed infiltrates the surrounding indigenous vegetation and spreads throughout it indigenous plant species are progressively lost until little else remains but the weed. Indigenous mammals, birds and insects soon become locally extinct as their food sources and preferred nesting sites etc disappear. They are often replaced by feral animals such as rabbits, foxes and rats.

            It is important to note here that the process of invasion by environmental weeds is aided by:

1. Land clearing

2. Soil disturbance, e.g. excavations

3. Dispersal of propagates (seeds, bulbs, rhizomes, stems, leaves) through:

   1. Mowing and slashing

   2. Earth moving

   3. Livestock & pets

   4. Wild animals

   5. Wind

   6. Water

   7. People - shoes & clothing

             This huge loss of biodiversity results in a greatly 'downsized' and simplified ecosystem that does not provide any where near the same level of 'ecosystem services'. Such an ecosystem has no where near the resilience of the original one. It is much more susceptible to continued degradation such as further weed invasion, salinity, erosion and loss of productivity.

              Once an ecosystem is degraded to this extent it requires huge amounts of effort and expense to halt the decline. It is rarely possible to restore the ecosystem to the same level of biodiversity, resilience and productivity.

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The Disaster of Prickly Pear

            Prickly pear (Opuntia) is in our history books as one of the most invasive weeds ever imported into Australia. It  had a devastating impact on life in rural eastern Australia during the early part of the 20th century. Special acts of Parliament were passed to enforce control measures in an attempt to halt its spread through Queensland and New South Wales. The story started over two hundred years ago.

Click here to read the full story on the North West Weeds website.

PPDC Inspector Jack Bailes standing in amongst a major common pear area - Scone 1938 (photo Norris J Small)

PPDC Inspector Alf Britton and large patch of rope pear - Cobar area 1938 (Photo NJ Small). Rope pear was a popular garden plant in dry areas...

The Victorian Catchment & Land Protection (CaLP) Act

            A subset of environmental weeds pose a major threat to agriculture, as well as the environment and biodiversity. Consequently the  CaLP Act declares these species as 'noxious weeds'.

          Landowners, whether private or public, have a statutory duty to control or eradicate noxious weeds from their property and/or road sides adjoining their properties.

            Here is the current list of declared noxious weeds for Victoria. For full details of these plants and the CaLP Act click here.

Noxious Weed Lists For Other States

• Northern Territory
• Tasmania
• New South Wales
• Western Australia
• South Australia (including feral animals)
• Queensland

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Other Environmental Weeds

             Environmental weed are only added to state noxious weed lists many years after their introduction when they are causing major problems for agriculture. Unfortunately by this time they have spread beyond any hope of eradication and the environmental damage is done.

             Worst still, some environmental weeds don't grow in major agricultural areas, and are unlikely to ever be added to the noxious weeds lists despite the devastating damage they do to our environment and our native flora and fauna.

             You may have heard the term 'sleeper weed'. This refers to exotic plants that are recognized as being potential environmental weeds within the conservation sector. Such plants may simply require sufficient time (perhaps decades) to be spread through retail distribution and garden escapes etc. Eventually these escaped populations reach a critical mass where reproduction and spread occurs rapidly.

            Awareness of environmental weeds is slowly growing within the general public and the nursery and landscaping sector, however change will not be fast enough to stop many hundreds or even thousands of new environmental weeds entering Australia. By the time we finally get serious about biosecurity we may have lost most of our native flora.

            Here is a list of environmental weeds in the Melbourne region as widely recognized by conservation workers and the environment departments of local councils. These are not yet declared as noxious weeds under the CaLP Act. Note the presence of popular garden plants in this list.