THE new Greens leader, Christine Milne, has pledged to expand her party's influence by building bridges with the rural and business communities, saying all these parties have more in common than they have ever acknowledged.
But her expansion plans do not extend to the ''old economy'' of the mining industry, which she said was mounting an unprecedented assault on the environment.
Senator Milne outlined her plans after the shock resignation yesterday of Bob Brown. After 16 influential years in federal politics, Senator Brown, 67, announced he had had enough. He stood down as party leader and said he would leave the Senate in June.
The Prime Minister, Julia Gillard, who has suffered politically because of her minority government's dependence on the Greens, said the agreement between the Greens and the government stood but she would not accede to any unreasonable demands.
''We would expect them to conduct themselves responsibly and reasonably, working with the government to achieve big changes for the Australian people, including bringing the budget back to surplus and continuing to deliver services for Australian families,'' she said.
Senator Milne, a reputed tough operator, drove the negotiations that resulted in the carbon tax.
She has been a vocal opponent of planned tax cuts for big business to be contained in the budget on May 8 and is demanding greater reductions in diesel excise rebates granted to miners.
Senator Milne, who was raised on a dairy farm, is a Tasmanian, like Senator Brown. She said one of her first tasks would be to tour rural Australia to ''highlight that the Greens and farmers share many values and have much common interest. The Greens and the bush have misunderstood ourselves for some time. I'm going to try to put that right.''
But Senator Milne said there was a split between the old and new economies and her overture to business applied only to ''progressive businesses''.
''We are seeing the biggest assault on the environment in Australia we have seen in a very long time,'' she said.
''Not just because of climate change but because of the rapaciousness of the mining industry and the willingness of both the Liberal and Labor parties in Australia to cave in to the few.
''If ever the Greens were needed in Australian politics, in public life, in redefining the debate in Australia, it's now.''
Senator Brown leaves the party at its height, having established it as the third force in Australian politics, supplanting the now-extinct Australian Democrats.
It holds the balance of power in the Senate with nine senators and has one lower house MP, Adam Bandt.
While Senator Milne's ascension to the leadership was unanimous, Mr Bandt was elected the deputy leader, beating Scott Ludlam and Sarah Hanson-Young.
The opposition said the Greens would become even more left-wing under Senator Milne and had no kind words for Senator Brown.
The Opposition Leader, Tony Abbott, forecast the party would decline but continue to control Labor in the process.
''The Greens will continue to control this government … because the Gillard government is utterly dependent on the Greens for its rather tenuous hold on power.''
Senator Brown was confident the party would continue to grow and said his departure now would be good for renewal.
He said the abuse heaped on him in recent years by the opposition, talkback radio hosts and other detractors was ''small beer compared to what I copped in Tasmania in the 1980s, particularly as a gay member of the [State] Parliament''.
Senator Brown said he still planned to be an activist for the environment and looked forward to spending more time with his partner, Paul Thomas.
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