Deliberate grass fires 'socially accepted', says Forestry Commission Wales
It is "quite normal" for people to start grass or forest fires in parts of Wales and it has being happening for generations, claims a forestry expert.
Jake Morris of Forestry Commission Wales said it was seen by young people as a way of having fun and their parents and grandparents did it.
Mr Morris will present his theory on BBC Radio 4's Costing The Earth programme on Tuesday.
Meanwhile, the cause of a mountain fire in Pontardawe on Monday was accidental.
Mid and West Wales Fire and Rescue Service said 25 firefighters were called to Mynydd Marchywel at 19:00 BST, where forestry and grass was alight.
The fire service has received hundreds of calls about grass fires across Wales already this year.
Mr Morris was the co-author of a report last year which blamed bored youths in deprived areas for starting thousands of forest and grass fires in south Wales between 2000 and 2008.
Mr Morris said: "If you talk to local residents they will talk about setting fires as something their parents and their grandparents have always done.
"It seems to be treated as something that's quite normal by certain pockets or the local population.
"The problem in the modern context is particularly prevalent amongst young people and there it's associated with, again, with high levels of social deprivation.
"And if you talk to young people and to young fire setters they will constantly tell you that there's nothing to do and this is a way of having fun, of thrill seeking, of seeing how big an impact in terms of the numbers of fire engines, and if you can get a helicopter out then all the better."
Roger Graef, a criminologist, author and filmmaker, said young people started fires because it was exciting.
He said he had experience of problems on the Meadow Well estate in North Shields, in the north-east of England, where there had been riots in the early 1990s.
"It's a deprived area, there are lots of empty houses. The kids as young as six and seven would find it very exciting indeed to set fire to one of these houses and then sit next door and watch all the excitement when the firemen came," he added.
"The firemen knew exactly who they were. Two of them told us on camera, would you believe it, it was just thrill seeking."
Dave Burton, a fire officer from Pontyclun in Rhondda Cynon Taf, said he thought there was a "certain element of boredom" among people who started fires.
"As a fire service we've become more aware," he added.
"We don't put our blues and twos (sirens and flashing lights) on as much.
"We try not to make such a big fuss over it. We're obviously doing the education through the schools as well, so it's something we're trying to tackle head on."
A crackdown aimed at reducing the number of grass fires in parts of south and mid Wales over Easter was launched last month.