Boreal forest fires

A wildfire near the village of Venetie burns Tuesday, June 24, 2008.

FAIRBANKS — A new study of the Yukon Flats region has revealed that the world’s boreal forests are burning at an historically unprecedented rate. Not only that, but the authors concluded fire rates likely will continue to grow in coming decades.

Both fire frequency and the amount of total biomass burned are higher now than they have ever been in the past 10,000 years, according to the study, which was published Monday in the Proceedings of the National Academy of the Sciences.

The researchers chose the Yukon Flats region because fire frequency there has been higher than nearly anywhere else in the North American boreal forests.

The boreal forests, also known as taiga, stretch over most of Russia and Canada and through the Alaska Interior, just below the Arctic Circle. The boreal forest biome is by far the largest expanse of wooded area in the world, covering more than 10 percent (6.41 million square miles) of Earth’s total land surface. It also holds nearly a third of the world’s stored carbon.

The 450 fires Alaska has seen this year have burned more than 1 million acres — more than fires in all other 49 states combined, according to statistics from the National Interagency Fire Center.

Chris Maisch, state forester and director of the Alaska Division of Forestry, has been involved in Alaska forestry for more than 30 years. He said both the length of the fire season and the intensity of the fires has increased even just in the past decade.

“We’re observing change,” Maisch said. “There’s no doubt about it.”

The start of the statutory fire season used to be May 1, but the state was forced to move that up by a month in 2006. It also moved the end of the season forward to the end of August to prevent a budget increase, but according to Maisch they’ve had to request emergency funds multiple times to continue operating through September.

In the Yukon Flats, researchers sampled charcoal records from 14 separate lakes to infer biomass burning during most of the Holocene epoch — a geologic time-frame spanning from about 11,700 years ago to the present.

They combined these historical data with observational records of the past 60 years to reach their findings. Until now, the era of highest biomass burning took place about 800 years ago, in what experts refer to as the Medieval Climate Anomaly.

During that time temperatures were higher than normal, but not as high as they have reached presently.

Although a great amount of biomass burned during the Medieval Climate Anomaly, fire frequency was relatively low. Ryan Kelly, the paper’s lead author, said they believe this was in part because the forest was made up of less combustible deciduous trees.

The deciduous trees tend to move in to heavily burned areas following forest fires.

If temperatures continue to warm, as most climate models propose, areas like the Yukon Flats may not slow down, even with the less-combustible makeup, according to the study.

“Many studies (usually based on models) have predicted that fire frequency, fire severity and/or area burned will rise dramatically over the coming century,” Kelly said. “Given that most of our study area has burned recently already, it seems like this would require deciduous forest stands to burn more than they do at present, and some studies have suggested that will in fact happen.”

If temperatures continue to rise and fire activity continues to increase, the effect on both a local and global scale could be dramatic.

In Interior Alaska, Kelly predicted increased fire activity would lead to forest makeup shifting from coniferous species such as black spruce to deciduous species like aspen and birch. That could, in turn, change wildlife patterns throughout the Interior.

The increases have had noticeable effects in Alaska. The shrub line has moved farther north, Maisch said. Tundra fires have become more common and carry-over fires — where the burning continues below ground through winter — have been happening with increasing frequency.

The human population in the Interior has been increasingly inundated with smoke, which can cause and trigger respiratory problems.

Budget-wise, forest fires have eaten away at state and federal money. Only 10 days into the fiscal year this July, the forest service had spent $6.8 million fighting several project fires and had to apply for emergency funding, Maisch said.

On a global scale, Kelly said, the “vast quantity of carbon” released into the atmosphere by boreal forest fires could significantly affect the climate worldwide.

“Few areas have detailed paleofire records for comparing the Medieval Climate Anomaly to present, but the Yukon Flats does, and there we find that the current fire regime is beyond anything from the Medieval Climate Anomaly,” Kelly said. “That’s pretty compelling evidence that something unusual is going on today.”