Police are appealing for witnesses after travellers allegedly forced their way on to Kinson Common on Tuesday evening.
It comes as one of the councillors for the area questioned why such offences seemed to go unpunished.
But Dorset Police said that alleged law-breaking such as vandalism were investigated in the same way as any other case.
Kinson councillor, Dennis Gritt, right, told the Daily Echo: “It’s an act of vandalism, what they did to the gates, and I can’t understand why people cannot be prosecuted in that situation.”
He said, although it was the first traveller incursion on the common in around 10 years, he was also frustrated that little progress had been made on a solution to the issue in decades.
Fellow councillor, Ron Whittaker, who represents Throop and Muscliff and lives near the common, said he was equally frustrated – in this instance by the fact that the first available court date to seek eviction of the group that could be secured by the council was Wednesday, July 23.
Cllr Whittaker, right, said that it appeared that the common’s protected status counted for nothing.
Chief Inspector Mike Claxton said: “When policing unauthorised encampments (UAEs) Dorset Police applies the law in the same way to both UAEs and the settled community. Crime and antisocial behaviour will not be tolerated.”
Police confirmed that the council had reported the damage to the gate and it was being investigated.
A spokesman said it had been reported that the metal gate had been forced open – there was a failed attempt to cut a titanium padlock before casing around it was broken.
Any witnesses should call police on 101, quoting reference 15:407.