http://www.abc.net.au/news/2012-11-02/i ... es/4350896
Even these enviro groups see the need for designated areas for dirt bikes, although hearing farmers complain about weeds being spread by bikes is a tad ironic especially coming from canola growers. They mention clubs are not discouraging riders, well according to the state governments inaction it appears on the surface it isnt a problem

We have increasingly less public land to ride every year, anything we can access often gets trashed by a few so they fence it off. We have no public forests to ride in as such pretty much all of it has been locked up by the state government or councils. The ride parks are very few, boring, small, and full of lunatics or there are a few MX tracks.
http://www.motorcyclingsa.org.au/docume ... 121213.pdf
It seems from this paper there are many stake holders getting involved so it is now up to the reluctant state government to do something other than ignore the issue.
There has been a campaign steadily growing here to introduce designated marked tracks, recreational reg, enforcement of licencing and rego to reduce the idiots who ride illegally, cut fences and have no respect for anything.
So in the meantime any area I know of is kept a very close secret amongst a few, or we have to go 3+ hours out of Adelaide or head for Vic which is like Disneyland for us.