The role of phosphorus and heavy metals in the spread of weeds in urban bushlands: an example from the Lane Cove Valley, NSW, Australia

Weed invasion of bushland in the Lane Cove Catchment, to the north west of central Sydney, is related to contamination of the floodplain by heavy metals and nutrients, increased frequency of flooding resulting from the urban development that surrounds the bushland, and site disturbance. Weed species are significantly different between the floodplain areas and the disturbed hillslope areas, probably as a result of differences in soil pollution, microclimate, and the nature of the disturbance. Seed availability does not seem to be a critical factor in determining weed invasion and composition. Weed invasion of disturbed upland areas could be reduced by replanting native plants. For contaminated floodplains there is little that can be done to restore the original vegetation unless the source of pollution is removed, and even then some considerable time may be required before pollution levels in the floodplain sediments decline. Use of native mesic vegetation, which is more adapted to higher nutrient levels, may be necessary for the management of contaminated floodplains. Whether the introduction of stormwater control systems into new subdivisions can avoid the contamination of urban floodplains is uncertain. There is an argument for accepting the inevitable contamination of urban floodplains and deliberately managing landscape ecology for this eventuality.