Adult left in the room has big shoes to fill

BOB Brown is a giant of the environmental movement.

A former medical practitioner turned state MP in Tasmania, he was the brains behind opposition to the building of the Franklin River dam. He moved into federal politics, founded the Greens and grew the party to a point where it won nine Senate spots, a lower house seat and an influence-peddling alliance with the Gillard government.

Brown's departure now puts one-time school teacher and former Tasmanian state MP Christine Milne into the Greens leadership. She has big shoes to fill - in terms of replicating Brown's charisma and political adeptness.

Milne is an adult in the room in the Greens parliamentary caucus, to be sure. But she is no Bob Brown. She does not have his gravitas inside or outside of the party. Replicating Brown's achievements will be nigh impossible for Milne following on from the 2010 election performance, which instantly marks her as a step down from the party's founder.

Most challenging for Milne will be managing the factions within the party. Greens are divided into two tendencies - the so-called watermelons, red on the inside and green on the outside, and the traditional environmentalists such as Brown and Milne.

The watermelons are defined by social activism on issues such as refugees and wealth redistribution, and they are on the rise. They disproportionately dominate the party's membership, even though the voting base for the Greens is largely swelled by environmentally attuned voters, perhaps less supportive of the Greens' social agenda. Potential challengers to Milne's authority within the social activist grouping include Sarah Hanson-Young and former NSW MLC Lee Rhiannon.

Brown was always able to hold the watermelons at bay because of his stature. Milne will be able to do so only if she is elevated by electoral successes.

In Milne's favour is the quirkiness of the half-Senate voting system. Even though the Greens won six Senate spots at the last election, at the next election they need to win only three spots to emulate their 2007 performance, thereby retaining their current numbers.

When Don Chipp resigned as leader of the Australian Democrats in 1986, the fear was that new leader Janine Haines would struggle to fill his shoes. In fact, the Democrats had much growing yet to do, and Haines contributed to that process. Haines had instant charismatic appeal, including as Australia's first female leader of a political party. Milne has shown no such appeal so far. And Milne takes over a far more electorally successful political movement. She must match or better Brown's success if the Greens are to avoide going into decline.