Developing a strategy for rehabilitating riparian vegetation of the Hawkesbury-Nepean River, Sydney, Australia

Abstract

Situated on the southeastern coast at 34°S 151°E, Sydney was established in 1788 as Australia's first permanent European settlement. Clearing of natural vegetation and environmental degradation associated with the country's largest population concentration over the past 200 years have severely affected the nearby Hawkesbury-Nepean River. A strategy for rehabilitation of the riparian vegetation to conserve and enhance the natural conditions remaining along the river, with particular emphasis on habitat and natural biodiversity, has been developed. The study area encompassed the most modified part of the river, where it passes alternately through 80 km of sandstone terrain, where the natural vegetation of waterside scrub backed by open-forest remains largely unchanged, and 135 km of floodplain terrain, where most of the indigenous tall open-forest has been cleared and associated wetlands have been greatly modified. Indigenous riparian zone vegetation was recognized as critical to the maintenance of river health, providing a reservoir of biodiversity as a major value, upon which other values, including enhancement of water quality, bank stablility and erosion control, depend. As 47 per cent of study area riverbank was found to have less than 25 per cent tree cover, the strategy recommended that all remnant native vegetation and remnant native trees along the river be protected and that a substantial long-term aim should be the establishment of a 50-metre wide strip of native riparian forest vegetation on each bank along the full length of the river, to be linked ultimately with other areas of natural vegetation on the floodplain. To provide practical resources for revegetation, the strategy assembled a botanical database, including maps showing present tree cover and the past extent of floodplain vegetation types, descriptions and locations of sites where significant native riparian vegetation remains, ecological information on approximately 300 locally indigenous riparian and wetland plant species, guidelines on selection of appropriate species, replanting methods and determination of priorities at both site and landscape scale.