Wildfire field guide
Surface Fire vs Crown Fire vs Ground Fire: what is the difference?
The three terms describe the fuel layer where fire is burning: at the surface, below it in organic ground fuels, or above it in the tree and shrub canopy.
Three fuel strata
Where the fire burns changes how it behaves.
Wildland fire can burn through different vertical layers of fuel. NWCG terminology distinguishes surface fire, ground fire and crown fire according to the fuel stratum carrying combustion.
Burns loose surface debris and low vegetation such as leaves, dead branches, grass and shrubs.
Consumes organic material beneath the surface, including duff, roots or peat-like fuels.
Advances through the crowns of trees or shrubs, sometimes linked to the surface fire and sometimes able to propagate more independently.
Surface fire
The most common visible spread layer.
Surface fire travels through fuels above the mineral soil but below the main canopy. Its behavior can range from low-intensity creeping to fast, high-intensity spread depending on wind, slope, fuel continuity and fuel moisture.
Surface fire can also provide the heat needed to ignite ladder fuels and tree crowns.
Ground fire
Slow spread can still mean deep, persistent burning.
Ground fire burns organic material beneath the surface litter. USDA fire-behavior literature describes fuels such as duff, organic soils, roots and buried rotten wood as typical ground fuels.
Crown fire
Not every burning tree crown is the same thing.
NWCG distinguishes several forms of crown involvement:
- Passive crown fire: individual trees or groups torch as the surface fire passes, but the fire is still fundamentally driven by the surface phase.
- Active crown fire: a solid flame develops in the crowns and the surface and crown phases advance together as a linked unit.
- Independent crown fire: fire advances through the crowns without needing energy from the surface fire to sustain movement.
This is why seeing one tree torch does not automatically mean a sustained crown fire is running through the canopy.
Transition
Fire can move between fuel layers.
A wildfire is not locked into one category. A surface fire can ignite ladder fuels and torch into the canopy. Crown fire can later drop back to surface fire if canopy continuity, wind or other supporting conditions change.
Operational descriptions therefore need a timestamp and location: “crown fire observed” describes behavior at a particular place and time, not necessarily the entire incident.
Connect the concepts
Fire type, intensity and spread belong together.
Rate of Spread →See how quickly different portions of a fire can advance across the landscape.
Head, Flank and Rear →Understand why behavior can differ around one fire perimeter.
Spotting and Spot Fires →Learn how embers can create new ignitions beyond the main fire front.
Sources
NWCG and USDA terminology.
NWCG — Independent crown fire ↗
Published 21 September 2026.