Huge Eucs hey, head south from here, sydney and Melbourne got big ones.
You might want to see an Australian immigration officer/ visa guru type of guy first. Here's a link to the website
http://www.immi.gov.au/
This link is for working holiday makers and you have to be between 18 and 30 y.o. plus the country you are from must be listed.
http://www.immi.gov.au/allforms/visiting_whm.htm
Dig around on that site, what will be difficult is finding some-one to sponsor you for a temorary resident visa.
I know a company that did that and brought out a guy from Overseas (I wont say where coz some people will argue). It's a big risk as you only go on what they say, the guy was not up to speed and couldn't perform the job as well as he boasted. Cut a long story short the guy was flown back and all of this at the employers expense.
There's also a skills matching data base and Tree Surgeons are on the desired list for employment. Maybe you can list yourself.
I think you need to talk to some-one or spend some time on that site. I certainly am not in the position to sponsor you as that's a pretty heavy committment, but that doesn't mean others aren't, maybe you can visit and show employers what you are made of and then they'll sponsor you.
Most of the guys who have visited just hang out for a while, pick up a bit of cash etc but if you are looking for more than that you'll need to go by the book.
I hope I've helped.