The father of Lawson Schalm, the firefighter who torched the CN trestle bridge outside of Mayerthorpe last year, said he will always support his son.

"My family is dedicated to supporting Lawson 100 per cent, unconditionally," said Albert Schalm. "We love him very, very much."

Still, he acknowledged the difficulty in accepting that his son set 18 fires in and around the town over a 12-day period in April 2016.

"He let his community down," Schalm said. "It was a very sobering experience."

Defence lawyer Ed O'Neill entered guilty pleas in Mayerthorpe provincial court to each of four counts of arson while Lawson Schalm, now 20, stood quietly beside him.

Schalm joined the Mayerthorpe fire department when he was 15 and stood four feet 11 inches, while weighing 91 pounds, fire chief Randy Schroeder wrote in a community impact statement read in court by Crown prosecutor Dallas Sopko.

"I'll never forget the smile on his face," Schroeder wrote in the letter.

Chief devastated

When they realized Schalm was behind the string of arsons, Schroeder said he was devastated.

His was one of two community impact statements read in court Friday.

The other was from Karen St. Martin, Mayerthorpe's chief administrative officer.

She said the fires caused immense stress, fatigue and turmoil among volunteer firefighters, who later underwent counselling. They felt betrayed, she wrote in her statement.

Schroeder said firefighters were "running on vapours" responding to call after call, "wondering when the next call would come and where."

Many fires were at night and volunteer members had a tough time maintaining their day jobs, he said.

The cost of responding to the fires and psychological services for members amounted to $8,653.52.

Lawson Schalm is pictured in an image from a Facebook page listed under his name. (Supplied/Facebook)

Fires sparked by cigarette lighter

Schalm lit grassy areas on fire with his cigarette lighter, and while most were put out before they spread, the CN trestle went up in flames and was destroyed.

"The accused did not intend to light the trestle itself on fire," the agreed statement of facts said.

However Schalm's experience as a firefighter, meant "he was reckless as to whether the grass fire would extend to the trestle."

The trestle fire involved nearly 40 firefighters, water bombers and CN crews. One firefighter was taken to hospital for smoke inhalation.

Rebuilding the bridge cost CN $7,561,593.

Crown prosecutor Dallas Sopko asked for a five-year prison sentence, arguing that breach of trust is the most aggravating factor. O'Neill asked for 18 months and three years probation.

Judge Charles Gardner deferred sentencing, saying he disagrees with both the Crown and defence submissions and needs time to consider the statement of facts.

Gardner plans to deliver his sentence July 6.

In the meantime, Schalm will remain on bail while living with his parents.

Mayerthorpe, has a population 1,300 and is 120 kilometres northwest of Edmonton.