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Wildlife, Animals, and Plants |
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FIRE CASE STUDIES
1st CASE STUDY:
CASE NAME:Oregon sagebrush burn REFERENCE:Sapsis, D. B.; Kauffman, J. B. 1991 [83] SEASON/SEVERITY CLASSIFICATION:
fall (9/25/87)/moderate STUDY LOCATION:The study was located in the John Day Fossil Beds National Monument in eastern Oregon. Specific location was T 11 S; R 26 E; sections 31 and 32. PREFIRE VEGETATIVE COMMUNITY:The prefire vegetation consisted of a basin big sagebrush (Artemisia tridentata ssp. tridentata)/perennial bunchgrass community. The understory was dominated by Idaho fescue (Festuca idahoensis) and bluebunch wheatgrass (Pseudoroegneria spicata). TARGET SPECIES PHENOLOGICAL STATE:Based on seasonal development reported for basin big sagebrush in eastern Washington, new shoots of basin big sagebrush would have been developing at the time of this spring burn, and flowering would have been occurring at the time of the fall burn. SITE DESCRIPTION:Site characteristics were as follows: slope north slopes of 20-60% elevation 2,296-2,821 feet (700-860 m) soils clay loam mean annual precipitation (1978-1988) approximately 11 inches (290 mm)Preburn fuel loadings were as follows: fuel fall spring live sagebrush attached dead* 1.06 0.42 Total live* 4.11 1.67 foliage* 0.84 0.32 1-hr TL* 1.16 0.44 10-hr TL* 1.35 0.52 100-hr TL* 2.18 0.89 dead sagebrush 1-hr TL 0.11 0.11 10-hr TL 0.23 0.26 100-hr TL 0.50 0.46 Totals standing live* 4.11 1.67 standing dead* 1.96 1.26 grass/herbs 3.01 2.67 1-hr TL* 1.80 0.86 10-hr TL* 2.22 1.03 100-hr TL* 2.72 1.35 *difference significant at P < 0.05 TL= time-lag fuels FIRE DESCRIPTION:"The objective of this study was to quantify total aboveground biomass and to investigate the variable nature of fuel consumption and fire behavior in basin big sagebrush-dominated ecosystems resulting from burning under different levels of fuel moisture and plant phenology."
Burns were ignited with a drip torch in a strip head firing
pattern. Specific characteristics were as follows: fall spring flame length* (m) 4.14 1.74 fireline intensity (IFL)* (kW/m) 6441 883 reaction intensity (IR)(kW/m2) 591 346 flame height* (m) 2.17 1.12 flame depth* (m) 10.35 2.56 rate of spread* (m/s) 1.57 0.23 heat per unit area (kJ/m2) 3253 3935** total energy* (kJ/m2) 18,119 9,267*** residence time (s) 6.92 11.66 fuel consumption* (Mg/ha) 9.80 5.231 *significant difference at P less than 0.05% **Heat per unit area measured only during flaming phase of combustion ***Total energy is heat release per unit area during both flaming and smoldering combustion Weather conditions were as follows: date fall spring time of burn 9:35-13:45 12:35-15:26 temperature C 15-18 23-35 rel. humidity% 41-48 21-34 windspeed (kph) 0-15 0-17 fuel moisture content% soil surface 2.90 3.21 dead grass/herb 8.88 7.36 live grass -- 142.60 sagebrush foliage 97.19 186.02 10-hr TL 4.59 4.99Flame length in fall averaged more than 13 feet (4 m); in spring burns flame length averaged less than 7 feet (2 m). The rate of spread was 6 times faster in fall burns although the temperature was lower and relative humidity higher.
FIRE EFFECTS ON TARGET SPECIES:Virtually all aboveground biomass was consumed by fire. Fuel consumption was twice as much in the fall burns as in the spring burns. Approximately 85% of 10-hour fuels were consumed by the fall burn and 52% were consumed by spring burns. Fuel consumption was as follows: fall spring
fine fuels (Mg/ha) 3.64 2.76
(%) 94.54 92.31
1-hr TL (Mg/ha) 1.65 0.66
(%) 91.66 76.74
10-hr TL (Mg/ha)* 1.90 0.54
(%) 85.59 52.43
100-hr TL (Mg/ha)* 2.63 1.27
(%) 96.69 94.07
total* (Mg/ha) 9.80 5.23
(%) 92.54 83.95
*significant difference at P less than 0.05%
FIRE MANAGEMENT IMPLICATIONS:Fire in basin big sagebrush communities is described as "stand-replacing." Fires in sagebrush are variable in terms of fuel consumption and fire behavior. Many factors contribute to variability including fuel characteristics, weather, and topography. 2nd CASE STUDY:
CASE NAME:Spring and fall prescribed burning in basin big sagebrush REFERENCE:Sapsis, D. S. 1990 [90] SEASON/SEVERITY CLASSIFICATION:
Fall (9/25/87)/not specified STUDY LOCATION: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:Prefire vegetation was a basin big sagebrush (Artemisia tridentata ssp. tridentata)/Idaho fescue (Festuca idahoensis)-bluebunch wheatgrass (Pseudoroegneria spicata). Understory species included Idaho fescue, bluebunch wheatgrass, western yarrow (Achillea millefolium) and threadstalk milkvetch (Astragalus fillipes). TARGET SPECIES PHENOLOGICAL STATE:Not specified SITE DESCRIPTION:
Aspect - north FIRE DESCRIPTION:The objectives of this study were "to quantify fuel loads, environmental conditions, fire behavior, and vegetative response corresponding to these 2 (spring and fall burn) fire treatments." 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 (k/h) 0-15 0-17
Soil M.C. (moisture content, %) 2.90 3.21
Dead grass/herb. 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)* 6,441 883
Reaction intensity (heat release rate)
(kW/m2) 591 346
Flame height (m)* 2.17 1.12
Rate of spread (m/s)* 1.57 0.23
Heat/area in flaming front
(kJ/m2) 3,253 3,935
Total energy (flaming & smoldering)
(kJ/m2)* 18,119 9,267
Residence time (s) 6.92 11.66
Fuel consumption (Mg/ha)* 9.80 5.23
N/A = not available
* = significant at p <.05
FIRE EFFECTS ON TARGET SPECIES:The frequency of basin big sagebrush increased in spring burns one year after treatment. No increases were noted 2 years after fire in fall-burned units. According to Sapsis [90], "factors relating to the greater fire severity (e.g. consumption, total energy) in the fall burns reduced the rate and degree of reinvasion in the fall burn plots." Basin big sagebrush was completely eliminated by the fall burn. Spring burning resulted in an 84% decrease in density. Aboveground biomass (Mg/ha) for spring and fall burn units are as follows: Fuel Category Treatment Live basin big sagebrush fall spring attached dead* 1.06(0.12) 0.42(0.16) foliage* 4.11(0.48) 1.67(0.63) 1-hour TL* 1.16(0.19) 0.44(0.16) 10-hour TL* 1.35(0.22) 0.52(0.19) 100-hour TL* 2.18(0.25) 0.89(0.33) *significant difference between treatments at p less than 0.05% (numbers in parenthesis are the standard error of the group mean) TL=time-lag fuels FIRE MANAGEMENT IMPLICATIONS:Results suggest that fall burns which exhibited greater fire severity were most effective in reducing basin big sagebrush.
Related categories for SPECIES: Artemisia tridentata spp. tridentata | Basin Big Sagebrush |
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