ANCHORAGE, Alaska (AP) — Following a winter marked by little snow and warmer temperatures, fire crews on Monday were tackling two large wildfires burning on mostly treeless tundra in the southwest part of the state.

Weekend rain helped tamp down the lightning-caused fires that through Monday have burned 63 square miles in the Yukon Delta National Wildlife Refuge, about 50 miles northeast of the commercial hub town of Bethel.

Alaska gets fewer fires in tundra than in forests, and tundra fires tend to be smaller, but they are not unheard of, according to Fish and Wildlife Service fire ecologist Lisa Saperstein.

Tundra fires are more common in southwest Alaska, but rare in the far north, she said. In 2007, a lightning-caused fire burned 400 square miles in the Brooks Range in the North Slope in an area where lightning is an anomaly.

The current fires are burning about 400 miles south of where the 2007 fire took place. Both fires are located in a biologically dynamic area where waterfowl nest, Saperstein said.

"There's lots of vegetation," she said. "And where you have vegetation, it's fuel."

According to a 2013 report by the University of Alaska Fairbanks Cooperative Extension Service, climate change could be a factor in a growing number of fires in tundra ecosystems over the next century.

Since the current tundra fires are not threatening people or buildings, crews were expecting to depart from one of the fires on Monday and continue mopping up hotspots at the other larger blaze, fire information spokesman Tim Mowry said.

Many Alaska wildfires are allowed to burn themselves out without crews if they are remote and far from any infrastructure. The bigger of the two fires, for example, had grown to 39 square miles by Monday, but crews were not immediately assigned to fight it until it had grown to almost half that size, Mowry said.

The amount of snow that falls during winter can expose an area to higher risk of fire because there is less moisture in the ground.

"But you still need something to ignite it," Saperstein noted.

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This story has been corrected to say show that 2007 fire burned 400 square miles, instead of 400 acres.