populations from taking hold on the island. Land degradation According to Jared Diamond, "Australia's number-one environmental problem [is] land degradation". Land degradation results from nine types of damaging environmental impacts: Clearance of native vegetation Overgrazing by sheep Rabbits Soil nutrient exhaustion Soil erosion Man-made droughts Weeds Misguided governmental policies Salinization Logging and woodchopping Clearcutting of old growth forests is continuing in parts of Australia. This often involves the destruction of natural ecosystems and the replacement with monoculture plantations. Australia had a 2018 Forest Landscape Integrity Index mean score of 7.22/10, ranking it 46th globally out of 172 countries. Land clearing In the prehistory of Australia the Indigenous Australians used fire-stick farming which was an early form of land clearing which caused long term changes to the ecology. With European colonisation land clearing continued on a larger scale for agriculture – particularly for cattle, cotton and wheat production. Since European settlement a total of 13% of native vegetation cover has been lost. The extinction of 20 different mammals, 9 bird and 97 plant species have been partially attributed to land clearing. Land clearing is a major source of Australia's greenhouse gas emissions, and contributed to approximately 12 percent of Australia's total emissions in 1998. The consequences of land clearing include dryland salinity and soil erosion. These are a major concern to the landcare movement in Australia. The clearing of native vegetation is controlled by Federal laws (indirectly), State law and local planning instruments. The precise details of regulation of vegetation clearing differ according to the location where clearing is proposed. Soil salinity Soil salinity affects 50,000 km² of Australia and is predominantly due to land clearance. Waterway health The protection of waterways in Australia is a major concern for various reasons including habitat and biodiversity, but also due to use of the waterways by humans. The Murray-Darling Basin is under threat due to irrigation in Australia, causing high levels of salinity which affect agriculture and biodiversity in New South Wales, Victoria and South Australia. These rivers are also affected by pesticide run-off and drought. Australian waterways facing environmental issues Rivers and creeks in urban areas also face environmental issues, particularly pollution. Victoria Port Phillip (contamination – silt; sediment; toxins; household chemicals; garden chemicals; E. coli; litter; flotsam and jetsam) Yarra River (contamination – E. coli; litter – 13 traps; logging; erosion; salinity) Maribyrnong River (contamination – arsenic and heavy metals; litter