Ground char [Depth of burn]

n. Visual estimate of burn severity that serves as an indicator of potential root damage or soil heating.

 

  • Discussion

 

Ground char, also referred to as “depth of burn,” is a surrogate measure for the downward heat pulse into the soil and is used to determine burn severity and potential root damage (Ryan 1982).  Ground char is usually measured in ground char classes (see table 1 below). These classes, developed by Ryan (1982), describe the burn severity around the base of an individual tree as evidenced by post-fire soil and vegetation characteristics (see table 1 below).  The classes described in the National Park Service’s Fire Monitoring Handbook (USDI National Park Service 2001) can be assessed at the individual-tree level or plot level (see table 2 below).  

 

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Table 1. Ground char classes developed by Ryan (1982).

 

Ground Char Class

Substrate

Unburned

No visible effect to the soil. Fire did not reside on the area although some damage may have occurred to above ground tissues from convected or radiated heat.

Light Burn

Litter and duff layers are scorched or charred, but the duff is not altered over the entire depth.

Moderate Burn

Litter is completely consumed and the duff is deeply charred or consumed, but the underlying mineral soil is not visibly altered.

Deep Burn

Litter and duff are completely consumed and the structure and color of the mineral soil surface are visibly altered.

 

 

Table 2. Ground char classes in Fire Monitoring Handbook (USDI National Park Service 2001).

 

 

Substrate

Forest vegetation

Shrubland vegetation

Grassland vegetation

Unburned (5)

Not burned

Not burned

Not burned

Not burned

Scorched (4)

Litter partially blackened; duff nearly unchanged; wood/leaf structures unchanged.

Foliage scorched and attached to supporting twigs.

Foliage scorched and attached to supporting twigs.

Foliage scorched

Lightly Burned (3)

Litter charred to partially consumed; upper duff layer may be charred but the duff is not altered over the entire depth; surface appears black; where litter is sparse charring may extend slightly into soil surface but soil is not visibly altered; woody debris partially burned; logs are scorched or blackened but not charred; rotten wood is scorched to partially burned.

Foliage and smaller twigs partially to completely consumed; branched mostly intact.

Foliage and smaller twigs partially to completely consumed; branched mostly intact; typically, less than 60 percent of the shrub canopy is consumed.

Grasses with approximately two inches of stubble; foliage and smaller twigs of associated species partially to completely consumed; some plant parts may still be standing; bases of plants are not deeply burned and are still recognizable.

Moderately Burned (2)

Litter mostly to entirely consumed, leaving coarse, light colored ash (ash soon disappears, leaving mineral soil); duff deeply charred, but not visibly altered; woody debris is mostly consumed; logs are deeply charred, burned out stump holes are evident.

Foliage twigs and small stems consumed; some branches still present.

Foliage twigs and small stems consumed; some branches smaller branches (0.25-0.50 in.) still present; typically, 40 to 80 percent of the shrub canopy is consumed.

Unburned grass stubble usually less than two inches tall, and mostly confined to an outer ring; for other species, foliage completely consumed, plant bases are burned to ground level and obscured in ash immediately after burning.

Heavily burned (1)

Litter and duff completely consumed, leaving fine white ash (ash disappears leaving mineral soil); mineral soil charred and/or visibly altered, often reddish; sound logs are deeply charred, and rotten logs are completely consumed.

All plant part consumed, leaving some or no major stems or trunks; any left are deeply charred.

All plant parts consumed leaving only stubs greater than 0.5 in. in diameter.

No unburned grasses above the root crown; for other species, all plant parts consumed.

Not Applicable (-1)

Only inorganic material on site before burn.

None present at time of burn.

None present at time of burn.

None present at time of burn.

 

 

  • See Also

  • References

    • Ryan, K. C. 1982. Techniques for assessing fire damage to trees. In: Lotan, J., ed. Fire, its field effects: proceedings of the symposium sponsored jointly by the Intermountain Fire Council and the Rocky Mountain Fire Council; 1982 October 19-21; Jackson, Wyoming: Intermountain Fire Council: 1-11.

    • USDI National Park Service. 2001. Fire Monitoring Handbook. Boise, ID: National Interagency Fire Center. 283 p.

     

  • Notes

    • Author 

      Sharon Hood, Forester

      Rocky Mountain Research Station