CORVALLIS — Over the last 30 years, the landscape annually affected by forest fires has slowly increased across the Pacific Northwest, and in some regions, severe blazes account for a higher proportion of the area burned than in the past.

As a result, the ecology of some of the region’s forests is changing in unprecedented ways.

Scientists calculated that less than one-half of 1 percent of the region’s forest is subject to fire in any given year. But in a project using satellite imagery and ground-based tree inventories, they also found that, in areas historically dominated by low- and mixed-severity fires, nearly a quarter of the burned landscape was subject to patches of high-severity fires that often exceeded 250 acres in size.

Studies of fires prior to 1900 suggest that severe fires occurred over smaller patches of forest and accounted for a much smaller proportion of the total burned area than they do today.

To reach their conclusions, researchers analyzed images taken by the LANDSAT satellite between 1985 and 2010. The study evaluated burned area and fire severity in seven different ecosystems, ranging from high-elevation subalpine forests to those dominated by western hemlock, ponderosa pine and Douglas fir. Since high-severity fire kills trees outright, the scientists were able to link fire-related tree mortality to changes in images from year to year.

“Large fires can have significant social and economic costs, but they are also playing an important role in the ecology of our forests,” said Matthew Reilly, lead author and a post-doctoral researcher in the College of Forestry at Oregon State University.

“From a regional biodiversity perspective, they are enhancing diversity by creating early seral habitats (the first stage of forest development dominated by grasses, forbs and shrubs). These provide important habitats for species that depend on open conditions and fire-killed trees (or snags). Such habitats are very rare and dispersed across the region but are concentrated in hotspots of high-severity fire like Southwest Oregon, Santiam Pass in central Oregon, the North Cascades in Washington and more recently the Blue Mountains, following the Canyon Creek Complex fire near John Day.”

For the complete story, see the April 17 edition of The Observer.