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Wildlife, Animals, and Plants |
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FIRE CASE STUDIES
1st CASE STUDY:
CASE NAME:Controlling broom snakeweed with fire in New Mexico REFERENCE:McDaniel, K.C.; Hart, C. R.; Carroll, D. B. 1997 [70] SEASON/SEVERITY CLASSIFICATION:Spring (March-April)/not specified Summer (June-July)/not specified STUDY LOCATION:Burns were located near Corona, in central New Mexico. PREFIRE VEGETATIVE COMMUNITY:The prefire plant community was a blue grama (Bouteloua gracilis) grassland. Preburn associates included winterfat (Krascheninnikovia lanata), cholla (Opuntia imbricata), wolftail (Lycurus phleoides), sand dropseed (Sporobolus cryptandrus), bottlebrush squirreltail (Elymus elymoides), threeawns (Aristida spp.), scarlet globemallow (Sphaeralcea coccinea), and verbena (Verbena bracteata). TARGET SPECIES PHENOLOGICAL STATE:
Spring - broom snakeweed was in bud stage with little green foliage. SITE DESCRIPTION:
Average annual precipitation - 397 mm FIRE DESCRIPTION:Burning conditions:
spring summer
Air temperature 4.4-24.8oC 20.6-35.3oC
Wind 3-10 m/s 3-8 m/s
Relative humidity 13-45% 9-39%
Fine fuel biomass 176-850 kg/ha 290-786 kg/ha
Broom snakeweed biomass 16-2,510 kg/ha 59-1,500 kg/ha
Fine fuel moisture 4-16% 9-12%
Soil moisture 2-11% 2-13%
Soil temp. at 10 cm 4-20oC 21-33oC
FIRE EFFECTS ON TARGET SPECIES:Mortality and crown destruction were unrelated to shrub size, vigor, or proximity to other broom snakeweed plants. Mortality of broom snakeweed was related to duration of heat > 60 degrees C. As relative humidity, windspeed, and fuel moisture increased, heat decreased and broom snakeweed mortality declined. Specific results were as follows:
spring summer
Crown consumption 8% 66%
Plant survival
Aerial regrowth 2% 7%
Basal regrowth 33% 1%
No regrowth 65% 92%
Spring burns produced less average crown destruction (8%) and shrub mortality (65%) than did summer burns (66% crown destruction and 92% mortality). Following spring burns, larger branches were often only charred and most shrubs (92%) were not burned completely to the ground. On plants that survived spring burning, most (94%) produced shoots from the basal area at or near the surface. Broom snakeweed mortality averaged 65% after spring burns with a range of 28 to 97%. Spring fires with average thermocouple readings of less than 300 C reduced broom snakeweed by 50%. Temperatures in excess of 350 degrees C reduced broom snakeweed by more than 80%.
FIRE MANAGEMENT IMPLICATIONS:
The study revealed that "ideal weather conditions must converge before, during, and after a prescribed burning event in order to maximize broom snakeweed control and forage growth on these grasslands." Attempts to carry out prescribed burns were often unsuccessful due to unsuitable weather and poor fuel conditions. Often prescribed burning in central New Mexico can be difficult except under extreme weather conditions. Fires will not carry if blue grama, the primary fuel source, is green. Overall success depends on quantity and uniformity of fuel and the degree of desiccation. Deferral of grazing for at least one season prior to burning is suggested.
2nd CASE STUDY:
CASE NAME:Spring and fall prescribed burning in basin big sagebrush REFERENCE:Sapsis, D. S. 1990 [86] 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:Preburn vegetation was a basin big sagebrush (Artemisia tridentata ssp. tridentata)/Idaho fescue (Festuca idahoensis)-bluebunch wheatgrass (Pseudoroegneria spicata). Associated species included western yarrow (Achillea millefolium) and threadstalk milkvetch (Astragalus fillipes). TARGET SPECIES PHENOLOGICAL STATE:Not specified. SITE DESCRIPTION:
Aspect - north 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 (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/m sq) 3,253 3,935
Total energy (flaming & smoldering,
kJ/m sq)* 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 <0.05
FIRE EFFECTS ON TARGET SPECIES:Fall burns completely eliminated broom snakeweed. Broom snakeweed numbers on spring burns were reduced from 400/ha prior to burning to 112/ha the first postfire year. This represents a decrease of 72%. Results were as follows: Treatment 1987 1988 1989
(fall prefire) (spring prefire) (postfire yr 1)
Fall burn 500 0 0
Spring burn ND* 400 112
Control 889 1121 946
*ND = no data
Related categories for SPECIES: Gutierrezia sarothrae | Broom Snakeweed |
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