Life underground persists after severe forest fires

The "red soils" show up as light colored patches in this photo from the B&B Fire Complex. Their shape often outlines the location where downed logs or other debris burned.

Another piece of conventional wisdom about severe forest fires appears to be falling. First, Oregon State University professor Beverly Law showed this year that such fires emit far less carbon than had been assumed, closer to 10 percent of above-ground live carbon stocks instead of 30 percent. Now, two forest scientists — Jane E. Smith and Cassie L. Hebel — have shown that life persists in severely burned soils, contrary to the assumption that such soils are sterilized by intense heat.

According to the June 2010 issue of Science Findings from the Pacific Northwest Forest Service, the two OSU graduates have found that life in so-called “red soils” does take a major hit. In soil samples from the 2003 B&B Fire Complex in the central Oregon Cascades, nutrients (carbon, nitrogen and phosphorus) were depleted by more than two-thirds, and microbial abundance was about 60 percent less than in less severely burned “black soils.” Not surprisingly, plants take longer to recover in these conditions, but recovery does occur.

Hebel, who now works for Watershed Sciences in Corvallis, also showed that severe burning may affect competition between native and invasive species. Non-native plants do not grow as well in severely burned soils as they do black soils. In contrast, native plants grow as well in both types of soil and may thus have an advantage in red soils.

You can read more about Hebel’s research, which was conducted in affiliation with OSU’s Subsurface Biosphere Initiative.

Smith, who has MS (forest ecology) and Ph.D. (botany and plant pathology) degrees from OSU, is a research botanist with the PNW Research Station and continues to study soil recovery after fire and salvage logging.