An illegal bonfire may be the cause of a heathland fire on the same day the service offered a reward for details about another suspicious fire.
More than 30 firefighters tackled the blaze on Canford Heath on Thursday, which was fanned by strong winds.
Following another fire on 200 hectares of heathland on 19 March, police offered a reward of £1000.
Dorset Fire and Rescue said such fires "puts lives at risk".
Dave Cooper, Poole's watch manager, said: "There were signs of an illegal bonfire on the heath which was the most probable cause of this fire.
"It is vital that we work closely together as a community and the emergency services to stop this mindless destruction of our precious heaths and forests by arsonists.
"Not only is it absolutely devastating to the countryside but it puts lives at risk."