OKLAHOMA CITY (AP) — Oklahoma Forestry Services officials say 2017 is already among the most active years on record for wildfires.

The agency has responded to more than 800 wildfires so far that resulted in more than 450,000 acres of burnt woodlands and grasslands. That ranks in the top five wildfire seasons in Oklahoma, state forester George Geissler told The Oklahoman (http://bit.ly/2nAnxs8 ).

Geissler said the number could increase if the state sees "a bad summer season," noting that it doesn't take much for another 100,000 acres to burn, especially if the rain ends.

"It has been a very unusual year for us. This year we also had to bring in . personnel from 34 different states, in different capacities, to address the fires," Geissler said

The most common source of the wildfires has been human activity, including people welding or discarding cigarettes, or dragging chains along roads, Geissler said. A less common source has been high winds downing power lines, causing them to arc on dry vegetation.

Geissler noted that some of the fires were intentionally set.

"We know for a fact that someone was lighting fires in the eastern part of the state," he said, adding that no arrests have been made in connection to those fires.

The wildfires have burned acres of wooded areas, land used to feed livestock and thousands of miles of fences.

Geissler said it's difficult to determine what the damage costs are statewide because the fires have affected different terrain.