Most soil in Windy Fire’s path is moderately burned

USDA determines that 47% of soil impacted by the Windy Fire was moderately burned, 10% severely

PORTERVILLE – The Windy Fire’s effect on the earth in the Sequoia National Forest has been a mixed bag according to the USDA and U.S. Forest Service.

Last week their Burned Area Emergency Response (BAER) assessment teams stated that the “soil burn severity” map showed approximately 43% of the 97,456-acre fire are either unburned/very low and/or low, while 47% sustained a moderate burn severity and about 10% a high burn severity.

It is important to note that the BAER team assesses the effects on soils and not the effects to vegetation. Burn severity characterizes the soil surface and below-ground impact, whereas vegetation effects are determined based on mortality and vegetation canopy changes.

Changes in soil cover, water repellency and soil physical/biological changes determine the severity burn level of the soil. Changes in water repellency are a frequently-discussed fire effect. Water repellency is a natural soil property. Fire can increase the severity and thickness of the water repellent soil, significantly affecting post-fire water runoff.

Low burn severity indicates only partial consumption of fine fuels while litter coverage remains relatively intact on the soil surface. Burning time at the soil surface was short, leaving root systems and root structure undamaged. Vegetative recovery time in the low category will vary based on ecological community but is expected to recover in the short-term.

Moderate burn severity indicates nearly all soil cover of vegetative litter and fine fuels was consumed or converted to ash. Because soil cover is significantly reduced, accelerated water runoff is expected. Charring of the mineral soil occurs in moderate burn severity classification as well as shallow root burning. The extent of the burning of the leaves and needles on the trees (aka tree canopy) can be unpredictable and can range from high to relatively low mortality which is why a closer look at the ground is required to determine the actual severity level of the soil burn. Water repellency is often found at the surface and is increased for both in severity and thickness of the water repellent soils which reduces the ability of precipitation to infiltrate the soil surface.

High burn severity is the result of higher intensity fire behavior or longer burning time at the soil surface. As a result of the high heat, nearly all the soil cover of vegetative litter and fuels has been consumed leaving bare soil prone to the impacts of precipitation and resulting water runoff. The surface mineral soil has been reduced to powder (single grain) and often several inches thick. This single grain soil is very easily transported or moved during rain events resulting in excessive soil erosion and sediment loading in rivers, streams and creeks.

The roots in the high burn severity areas tend to be completely consumed by the resulting heat of the fire above the soil surface. Water repellency does not exist at the surface because water repellent compounds have been vaporized and tend to be found below the powdered soil surface, but the repellency thickness and more severe burning tend to be much greater than a Moderate SBS soil. Generally, there is 100% tree mortality in High SBS soils. Fire-adapted shrubs and vegetation such as bear clover, manzanita, and deer brush tend to come back with vigor because of root sprouts. However, because seed sources are consumed in these High SBS areas, conifers may take many years to re-establish without tree planting.

BAER assessment teams are multi-disciplinary teams sent to federal lands following significant wildfires. Their role is to characterize the fire effects to watersheds, identify imminent post-fire threats to human life, safety, property, infrastructure, critical natural and cultural resources. Once the assessment is complete, the team develops BAER emergency treatment recommendations to mitigate identified risks. After the assessment, local land managers work with other BAER team members to implement and the assessment team’s recommended treatments and action stabilization measures.

The team begins their assessment immediately after the fire threat passes. According to the USDA the burn severity map also shows the acreage for each of the landowners for the 97,456 acres to be: 75,275 acres for the Sequoia National Forest; 19,401 acres for the USDI Bureau of Indian Affairs; 1,774 acres of private/other lands; and 1,006 acres for the USDI Bureau of Land Management.

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