Single Publication

BAER Team Special Report - Soil Burn Severity vs. Vegetation Mortality

The Burned Area Emergency Response (BAER) team measures two different elements, soil burn severity and vegetation mortality, to help guide their assessment of emergency risks and imminent threats to critical values, including life and safety, Forest Service property and critical natural resources following a wildfire.

Soil Burn Severity: We tend to think of wildfire burn severity in terms of the visual impacts to above-ground vegetation, but the post-fire landscape response (erosion, flooding, and mass movement) is generally more strongly correlated to soil burn severity. Soil burn severity is a critical indicator of recovery.

Even when the soil looks lifeless, fine, hair-like roots can still persist beneath the surface. These roots not only store energy for fire-adapted plants to recover more quickly after a fire, but they also act as a net that can help stabilize the soil against erosion. When assessing soil burn severity, soil scientists examine the condition of these fine roots to help determine post-fire recovery and likelihood of erosion. 

Pre-fire ground cover, forest type, fire behavior, slope, aspect, and other factors all influence soil burn severity. The BAER team’s watershed specialists (soil scientists, hydrologists, and geologists) use these factors to help ground-truth different burn intensities to tease out patterns of how fire affected and changed the properties of the soil. From the soil burn severity map, geologists can predict debris flow hazards, hydrologists can predict changes to stream flows, and soil scientists can predict erosion potential.

Vegetation Mortality: Above ground vegetation can aid in the recovery of a burned forest. For example, in areas where the trees were scorched and killed, those conifer trees will drop their needles, which provides very helpful natural ground cover. Since post-fire soil erosion is a major concern of soil scientists, this natural ground cover plays a crucial role in slowing the interaction between rain drops and soil particles that would otherwise get washed down the hillslope.

The BAER team creates a vegetation mortality map that focuses on the wildfire effects to the forest and is reported in percent of basal area loss. Basal area is the average amount of an area (such as an acre) occupied by tree stems. This product helps other scientists, such as wildlife biologists, botanists, and silviculturists understand what to expect from this changed landscape for wildlife habitat, invasive weeds, and timber production.

While lots of trees and other vegetation died, nature is resilient, and we’ve already seen evidence of many plant species sprouting up amongst the newly blackened and open canopy forest.