Llantysilio mountain moorland's 'heartbreaking' 4x4 damage
Protected heather moorland in Denbighshire has been damaged by vehicles being driven off-road.
A number of areas in the Llantysilio mountains had been restored and countryside managers said it was "heartbreaking" to see the damage.
The moorland is internationally recognised and home to a number of rare species, as well as agricultural land for farmers.
North Wales Police said anyone with information is asked to call 101.
Around three quarters of an acre of land was restored in 2010 alongside the Moel y Faen quarry near the Ponderosa Cafe above Llangollen.
However, following the incident, the grass has been removed in places, soil has been churned up and there are tyre tracks going all the way up the restored area.
"It is heartbreaking to see our efforts so badly damaged in an instant," said Nick Critchley, moorland field officer for the Heather and Hillforts Project.
He said the council's countryside service had been working "tirelessly" with officers from North Wales Police to tackle problems with off-roaders using vehicles illegally in the area, and had "some considerable success".
Volunteers, conservation and off-road user groups had been involved in repairing the damage caused, and there had been plans to spread more heather this spring, he added.
"However, this latest incident shows the message simply isn't getting through to a minority of individuals who think it's appropriate to damage our countryside.
"Heather moorland is internationally rare, is home to a number of rare species, is important agricultural land for many farmers and crucially is very slow growing."
Mr Critchley said it would take "many years" for areas damaged in this way to recover.
"We must work together to tackle this anti-social behaviour," he added.
Off-road vehicle users should ensure they know where they can drive legally before they set out.
"I urge other users of the countryside to contact the police if they see vehicles being used beyond the network of roads and byways available to off-road vehicles," he said.