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: