The original tree, believed to be 116 years old, had its roots damaged when the Octagon was upgraded in the late 1980s, and it was affected by the common plane tree fungus, anthrac nose.
Council community and recreation services manager Mick Reece said the replacement came from an embankment at the Southern Motorway beside Carisbrook.
It had to be a mature tree to make it "people-proof", and less likely to be vandalised.
Because of the work required to move such a large tree, the cost of the exercise was $4000.