Environmental Weeds - The Nature of the Problem

Plants growing in their natural habitat have evolved in association with a range of other organisms...other plants, fungi, insects, birds, micoorganisms...they are part of a balanced ecosystem which exerts controls on the growth and development of the plants. Those controls may limit the rate of growth of a plant and its reproduction in a number of ways. Fire may routinely destroy parts of the ecosystem, requiring the plants to regularly re-establish; insects, bird and animals may eat a large portion of the seed; insects may damage the plants so that much of the plant's energy goes into repair of damaged tissues.

When a plant is taken to some other geographical area, whether within the same country or overseas, all or part of those other components of the ecosystem will almost certainly not be present. Under such circumstances, plants may grow more vigorously and spread more rapidly than they can in their natural environment. If they escape from cultivation, mainly through seeds being spread by wind, by birds or by gardeners disposing of garden wastes in bushland (or on land which drains to bushland), they are potential pest species. The development from a potential pest to an actual pest may take many years to occur or it may never occur. Unfortunately, if a plant does become a pest species, by the time the threat is recognised it is often difficult to develop effective control strategies.

	In their natural habitat, species in the "Black Wattle" group such as Acacia parramattensis are subject to attack by borers. Without this control, this and other species have become weeds overseas. Photo: Brian Walters

Of course, most exotic plant species do not become weeds. People all over the world cultivate plants from all parts of the globe and it is relatively few that end up causing problems. Other controls such as climate and soils may restrict their growth. But the potential for problems is there.

Are Australian plants any different to plants native to other parts of the world in their potential to be weedy?

There's no reason why they should be, but introducing any untried plant into a new environment always involves an element of risk, no matter where the plant originated. To minimize the possibility of YOU being responsible for the introduction or spread of a weed, perhaps the following suggestions could be considered:

• Grow indigenous plants. These are plants native to your particular geographical area but, unfortunately, it's not always easy to obtain these plants from nurseries....you may need to seek out local revegetation groups or grow the plants yourself.
  
  
• Grow plants that are well established in the horticultural trade in your area. These are likely (but not certain) to have proven themselves non-invasive.
  
  
• Become familiar with weed lists for your local area and avoid any plants listed (just because they are listed does not necessarily mean they won't be available from a nursery). These lists may not always be available but a check with a local agricultural department or local government authority may be useful.
  
  
• If you plan to grow a species not normally cultivated in your area (eg. by importing seed from Australia or elsewhere), check with a local botanic gardens, agricultural department, weed control council, National Parks Authority or botanical faculty at a University as to the potential for the species to become invasive.
  
  
• If you're satisfied that there is minimal threat and go ahead and cultivate a new plant in your district (particularly if the garden is near natural bushland), keep it under observation. If it looks like it may become rampant through suckering or prolific seed formation and germination, be ruthless!
  
  
• If in any doubt....DON'T PLANT! It's not worth the risk!