Dorset Fire and Rescue Service say that arsonists are believed to have started a fire which destroyed heathland on Ham Common in Poole yesterday.
Large fires at Canford Heath and Studland are also thought to be the result of individuals deliberately starting fires.
The service is calling on people to recognise the serious danger posed by the wild fires to people and property.
The South's latest landmark, costing £40m, officially opens today. The Twin Sails in Poole is designed to ease congestion between the town and Hamworthy. Celebrations are planned to mark the opening, with a visit from the Princess Royal on Monday