The fire burned two hectares of young pines in the Flagstaff Forest near Whare Flat about 5pm on Saturday, November 30.
Three helicopters were used to fight the blaze, which City Forests chief executive Grant Dodson described as a ''callous act''.
A scene examination indicated that the fire was deliberately lit, police said in a statement today.
Police believe members of the public in the area at the time may be able to help with the investigation.
Anyone with information is asked to contact Dunedin Police on 471 4800.
Information can also be provided anonymously to Crimestoppers on 0800 555 111.