Burn Severity
From a landscape perspective, burn severity is defined as the degree of environmental change cuased by fire. Heterogeneity in burn severity is a result of the spatial variation of factors such as fire intensity, topography and vegetation type. Burn severity can be broken down into several categories, useful in gauging post burn ecological responses:
- Unburned
- Low Severity Burn
- Medium Low Severity Burn
- Medium High Severity Burn
- High Severity Burn
| Rank | Burn Severity | Description | Characteristics |
|
0 |
Unburned |
Fire extinguished before reaching microsite |
• Leaf litter from previous years intact and uncharred • No evidence of char around base of trees and shrubs • Pre-burn seedlings and herbaceous vegetation present. |
|
1 |
Low Severity Burn |
Surface fire which consumes litter yet has little effect on trees and understory vegetation. |
• Burned with partially consumed litter present • Evidence of low flame heights around base of trees and shrubs (<0.5 m) • No significant decreases in overstory & understory basal area, diversity or species richness from pre-burn assessments • Usually burning below 80 ° C |
|
2 |
Medium-Low Severity Burn |
No significant differences in overstory density and basal area, & no significant differences in species richness. However, understory density, basal area, and species richness declined.
|
• No litter present and 100% of the area covered by duff • Flame lengths < 2 m • Understory mortality present, little or no overstory mortality |
|
3 |
Medium-High Severity Burn |
Flames that were slightly taller than those of Medium-low intensity fires, but these fires had occasional hot spots that killed large trees, With significant reduction in the understory |
• Soil exposure on l-50% of the area • Flame lengths <6m • High understory mortality with some overstory trees affected |
|
4 |
High Severity Burn |
Crown fires, usually a stand replacing burn with relatively high overstory mortality |
• Soil exposure >50% • Flame lengths >6m • Higher overstory mortality >20% • Usually burning above 800 ° C |