AllRefer - Species: Western Juniper | Juniperus occidentalis: FIRE CASE STUDIES

The study was located approximately 5 miles (10 km) west of Dayville in east-central Oregon. The site was located in John Day Fossil Bed National Monument in T 11 S R 26 E , sections 31 and 32.

PREFIRE VEGETATIVE COMMUNITY:

Preburn vegetation was a basin big sagebrush (Artemisia tridentata ssp. tridentata)-Idaho fescue (Festuca idahoensis)-bluebunch wheatgrass ((Pseudoroegneria spicata) community. Dominant understory species included Idaho fescue, bluebunch wheatgrass, yarrow (Achillea millefolium) and threadstalk milkvetch (Astragalus fillipes). Western juniper (Juniperus occidentalis) did not occur as a dominant or codominant in the prefire vegetative community. Western juniper presumably grew as scattered individuals (many of which were seedlings). Prefire cover of western juniper was 369 individuals per ha.

TARGET SPECIES PHENOLOGICAL STATE:

SITE DESCRIPTION:

Aspect - north
Slope - 20-65%
Elevation - 2,297-2,625 feet (700-860 m)
Soils - very stony, clay-loams
Annual precipitation - 10-14 inches (250-360 mm)

FIRE DESCRIPTION:

Both burns were ignited with drip torches using a strip-head firing pattern. Pretreatment fuel loads ranged from 5-12 Mg/ha. Fuel loads in fall treatment units averaged 10.5 Mg/ha and in spring treatment units, fuel loads averaged 6.2 Mg/ha. Large amounts of herbaceous fuels (> 3 Mg/ha) were present.

Burning Conditions:

	Fall	Spring
Time of burn	9:35-13:45	12:35-15:26
Temperature (^oC)	15-18	23-25
Relative humidity (%)	41-48	21-24
Windspeed (km/h)	0-15	0-17
Soil m.c. (moisture content, %)	2.90	3.21
Dead herbaceous m.c.*	8.88	7.36
10-hr timelag m.c.	4.59	4.99
Sagebrush foliage m.c.*	97.19	186.02
Live grass m.c.	n/a	142.60

Fire Behavior:

	Fall	Spring
Flame length (m)*	4.14	1.74
Fireline intensity (kW/m)*	6441	883
Reaction intensity (heat release rate, kW/m²)	2.17	1.12
Flame depth (m)*	10.35	2.56
Rate of spread (m/s)*	1.57	0.23
Heat/area in flaming front (kJ/m²)	3253	3935
Total energy (flaming & smoldering, kJ/m²)	18,119	9267
Residence time (s)*	6.92	11.66
Fuel consumption (Mg/ha)*	9.80	5.23

n/a=not available
*significant difference between fall and spring burning (p<0.05)

FIRE EFFECTS ON TARGET SPECIES:

Both spring and fall treatments killed all western juniper:

Treatment Density/ha

1987 1988 1989

fall 456 0 0

spring n/a 369 0

control 733 733 1040

(difference between treatments not significant at p<0.1)

Western juniper frequency (%):

1987 1988 1989

4 0 0

FIRE MANAGEMENT IMPLICATIONS:

Prescribed fire was effective in limiting the abundance of western juniper. Prescribed fire may represent an effective and economical management tool for rangelands.

FIRE CASE STUDIES

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