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Fort Hood Center for Cooperative Ecological Research
1996 Crown Fire
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On 21 February 1996 three fires were reported on separate ranges in the Live Fire Area on Fort Hood. Fires are common in this area as they are sparked by artillery training activities. These fires usually only burn small areas of grassland. However, on this particular day, the fires quickly burned from grasslands into woodlands, becoming crown fires, and burning habitat of federally listed golden-cheeked warbler (Dendroica chrysoparia).
The reasons that these fires spread so quickly included drought conditions, record-breaking high temperatures, low relative humidity, and gusting winds. Click here to see weather data.
The army, required to suppress any fire that threatens endangered species habitat, quickly acted to put out the fires.
Due to unusual weather conditions, the fires proved difficult to stop. The army Fire Department, with the help of 22 fire departments from surrounding communities, extinguished the fire on March 7, after 15 days. This picture shows what areas of warbler habitat looked like immediately after the fire.
Objectives
The objectives of this study are to determine the extent of the fire using GIS and to monitor long-term vegetation succession.
Mapping Methods
To map the extent of the fire, we used custom aerial photographs to digitize polygons on-screen in ArcView. Using the resulting GIS layer, the area of the polygons was totaled and it was determined that 4,015 ha (9,921 acres) burned. This layer was then combined with the pre-burn endangered species habitat layer to determine the loss of endangered warbler habitat. A total 2,313 ha (5,783 acres) of golden-cheeked warbler habitat burned.
Vegetation Methods
For long-term vegetation monitoring, we selected sites that were heavily burned by the fire and that had been classified as warbler habitat prior to the fire.
We established 65 permanent transects and assessed burn severity ratings soon after the fire. Vegetation regrowth was measured that year, every year since, and will continue many years into the future.
To assess burn severity, we followed the methods presented by National Park Service (1992). Burn severity codes were recorded for substrate and vegetation using the burn severity matrix. Plots were assigned a severity rating of 5 through 1 depending on severity of the burn.
Burn matrix
| Unburned (5) |
Scorched (4) |
Lightly burned (3) |
Moderately burned (2) |
Heavily burned (1) |
|
| Substrate (litter, duff) | not burned |
litter partially blackened; duff nearly unchanged; wood and leaf structures unchanged |
litter charred to partially consumed; upper duff layer burned; wood and leaf structures charred, but recognizable |
litter mostly to entirely consumed, leaving coarse, light colored ash; duff deeply burned; wood and leaf structures unrecognizable |
litter and duff consumed, leaving fine white ash; mineral soil visibly altered, often reddish |
| Vegetation (understory, brush, herbs) | not burned |
foliage scorched and attached to supporting twigs |
foliage and smaller twigs partially to completely consumed |
foliage, twigs, and small stems consumed |
all plant parts consumed leaving some or no major stems and trunks |
To select transect locations, we generated random points in ArcView, using the habitat loss layer.
We further subdivided the landscape based on aspect, slope, and soil.
Class table
| Class | n | Aspect | Soil |
| 1 | 12 | level (slope <4%) | Evant silty clay |
| 2 | 10 | level (slope <4%) | Eckrant-Rock outcrop complex |
| 3 | 10 | north (slope ³4%) | Eckrant-Rock outcrop complex |
| 4 | 10 | south (slope ³4%) | Eckrant-Rock outcrop complex |
| 5 | 13 | north (slope ³4%) | Real-Rock outcrop complex |
| 6 | 10 | south (slope ³4%) | Real-Rock outcrop complex |
Transects were 100 m in length. The beginning and end points were permanently marked with T-posts and metal tags, the locations recorded using a DGPS unit, and photographs were taken.
Woody vegetation regrowth consisted of stump and root sprouts growing from individuals whose roots survived the fire, with few woody species regrowing from seed.
In order to the avoid difficulties associated with identification of separate genetic individuals, woody sprouts were counted by size. Thus, root and stump sprouts were not distinguished from seed sprouts.
The sizes used for woody vegetation were:
- seedling - woody plant <0.3 m tall.
- shrub - woody plant³ 0.3 m tall and <1.8 m tall.
- sapling - woody plant³ 1.8 m tall and dbh <5 cm.
- tree - woody plant³1.8 m tall and dbh ³5 cm (no trees have been sampled yet).
Seven plots (25 sq m) were set up along each transect and sampled. Within each vegetation size, species were listed, the count total of sprouts was recorded, and density was calculated.
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