SPECIES: Gutierrezia sarothrae
Tirmenstein, D. 1999. Gutierrezia sarothrae.
In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
The fully documented scientific name of broom snakeweed is Gutierrezia sarothrae (Pursh) Britt. & Rusby (Asteraceae) [103,102]. Several varieties are recognized [51,50]:
Gutierrezia sarothrae var. microcephala (DC) L. Benson
Gutierrezia sarothrae var. pomariensis Welsh
Gutierrezia sarothrae var. sarothrae
Broom snakeweed intergrades with California matchweed (G. californica) in parts of southern California and northern Mexico .
No special status
Broom snakeweed grows from Saskatchewan and Alberta through the Rocky Mountains and the Great Plains . It extends southward into California and central Mexico, and eastward to Texas, Kansas, and Nebraska [20,25,65]. It is widely distributed in the Mojave Desert and reaches northward into the Great Basin .
FRES21 Ponderosa pine
FRES30 Desert shrub
FRES34 Chaparral-mountain shrub
FRES36 Mountain grasslands
FRES38 Plains grasslands
FRES40 Desert grasslands
FRES28 Western hardwoods
FRES33 Southwestern shrubsteppe
AZ CA CO ID KS MT NE NV NM ND
OK OR SD TX UT WA WY AB MB SK
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
K016 Eastern ponderosa pine
K017 Black Hills pine forest
K018 Pine-Douglas-fir forest
K023 Juniper-pinyon woodland
K037 Mountain mahogany-oak scrub
K038 Great Basin sagebrush
K041 Creosote bush
K046 Desert: vegetation largely lacking
K055 Sagebrush steppe
K056 Wheatgrass-needlegrass shrubsteppe
K057 Galleta-three-awn shrubsteppe
K058 Grama-tobosa shrubsteppe
K063 Foothills prairie
K070 Sandsage-bluestem prairie
K074 Bluestem prairie
K081 Oak savanna
K098 Northern floodplain forest
210 Interior Douglas-fir
236 Bur oak
237 Interior ponderosa pine
302 Bluebunch wheatgrass-Sandberg bluegrass
303 Bluebunch wheatgrass-western wheatgrass
310 Needle-and-thread-blue grama
314 Big sagebrush-bluebunch wheatgrass
320 Black sagebrush-bluebunch wheatgrass
322 Curlleaf mountain-mahogany-bluebunch wheatgrass
323 Shrubby cinquefoil-rough fescue
324 Threetip sagebrush-Idaho fescue
503 Arizona chaparral
505 Grama-tobosa shrub
604 Bluestem-grama prairie
611 Blue grama-buffalograss
701 Alkali sacaton-tobosagrass
703 Black grama-sideoats grama
704 Blue grama-western wheatgrass
705 Blue grama-galleta
707 Blue grama-sideoats grama-black grama
712 Galleta-alkali sacaton
724 Sideoats grama-New Mexico feathergrass-winterfat
725 Vine mesquite-alkali sacaton
Broom snakeweed is a common constituent of many early seral sagebrush (Artemisia spp.)-grassland, pinyon-juniper (Pinus spp.-Juniperus spp.), and desert shrub communities. It has been identified as an indicator in early to late seral communities of northern New Mexico. Codominants include one-seed juniper (J. monosperma), big sagebrush (Artemisia tridentata), black sagebrush (A. nova), winterfat (Krascheninnikovia lanata), ovate saltbush (Atriplex obovata), blue grama (Bouteloua gracilis), black grama (B. eriopoda), galleta (Hilaria jamesii), sand dropseed (Sporobolus cryptandrus), alkali sacaton (Sporobolus airoides), and western wheatgrass (Pascopyrum smithii) .
Broom snakeweed occurs most commonly with creosote bush (Larrea spp.), honey mesquite (Prosopis glandulosa), yucca (Yucca spp.), rabbitbrush (Chrysothamnus spp.), big sagebrush, black sagebrush, shadscale (Atriplex confertifolia), pinyon, juniper, oak (Quercus spp.), Indian ricegrass (Achnatherum hymenoides), grama, and buffalograss (Buchloe dactyloides) [62,97].
Broom snakeweed is listed as a dominant or indicator in the following classifications:
Natural production potential of some Rio Puerco soils in New Mexico 
Phyto-edaphic communities of the Upper Rio Puerco Watershed, New Mexico 
Broom snakeweed provides little browse for domestic livestock . It is of minimal value to cattle and horses  but does provide fair quality winter browse for domestic sheep when green forage is scarce or lacking [62,71]. Utilization by domestic sheep on winter ranges of Utah and Nevada may reach 9.8% to 15% [41,47]. However, Green and others  report only light (less than 3%) use by domestic sheep in west-central Utah. Summer Angora goat use may be fairly heavy on burned-over Arizona chaparral .
Broom snakeweed can be toxic to domestic sheep, goats, and cattle particularly during winter or early spring when poor forage availability forces animals to consume large quantities [15,62,95]. Domestic goats are fairly resistant to broom snakeweed toxicity . Saponins present in the foliage can cause illness, death, or abortion in livestock [95,100]. However, toxicity apparently varies with phenological stage and substrate. Higher toxicity levels are often associated with periods of rapid growth, such as early leaf development, and with growth on sandy rather than calcareous soils . Broom snakeweed is also a secondary or facultative absorber of selenium which may cause illness or death when consumed in quantity . Carpenter and others  report that “production losses from snakeweed poisoning are not significant with only a light infestation."
Broom snakeweed provides only poor quality browse for most large ungulates. It is however, important to pronghorn in some areas, particularly during spring and summer. In parts of Utah, pronghorn utilization may reach up to 28% . Broom snakeweed is considered a preferred pronghorn food in Carter County, Montana from September through December and is eaten in March in northeastern Colorado [87,96]. Broom snakeweed is eaten by mule deer in some big sagebrush-grass communities of northern Utah and south-central New Mexico [4,59]. It receives moderate use by desert mule deer in parts of Texas and Arizona . Broom snakeweed is a winter food source for bighorn sheep on the Cinnabar winter range of Montana . In northeastern Colorado, bison consume broom snakeweed particularly during March and October [79,80].
Broom snakeweed is a major food source for black-tailed jackrabbits in Kansas and south-central New Mexico [22,27]. In a New Mexico study, use of broom snakeweed by the black-tailed jackrabbit was highest in summer and winter .
Broom snakeweed seeds are readily eaten by a wide variety of small birds and mammals. Seeds of broom snakeweed are an important winter scaled quail food in parts of southeastern New Mexico . Broom snakeweed seed forms part of the spring and summer diets of the lesser prairie chicken in eastern New Mexico . The banner-tailed kangaroo rat, Ord’s kangaroo rat and northern grasshopper mouse also eat broom snakeweed seed [7,70].
Broom snakeweed browse is relatively unpalatable to most big game species and to domestic livestock. However, results of a Utah study indicate that it is preferred by pronghorn during spring and summer . Broom snakeweed is described as "at least moderately palatable" to domestic sheep in Idaho . Seeds are palatable to a variety of small birds and mammals. Palatability of broom snakeweed has been rated as follows :
CO MT ND UT WY Cattle poor poor poor poor poor Sheep fair poor poor fair poor Horses ---- poor ---- poor poor Pronghorn ---- poor poor fair ---- Elk ---- poor ---- poor ---- Mule deer ---- poor poor fair ---- White-tailed deer ---- ---- poor ---- ---- Small mammals ---- ---- ---- fair ---- Small nongame birds ---- ---- ---- fair ---- Upland game birds ---- ---- ---- poor ---- Waterfowl ---- ---- ---- poor ----
Protein Crude Ca Phosphorus (%) Fiber (%) (%) (%) Before grazing 6.62 24.0 1.13 .079 After grazing 6.53 24.8 1.13 .079Seasonal differences in nutritional content have been reported as follows :
Protein Ether Ash Ca P K Mg Mn % Extract% % % % % mg/kg--- November 11.8 11.9 5.3 0.69 0.18 1.38 40 140 December 8.4 7.3 4.4 0.62 0.13 0.91 27 298 March 15.2 4.9 14.7 1.32 0.24 2.74 69 1427Differences in crude protein level (%) according to plant part and season have also been reported :
3/29 4/9 4/24 5/18 5/26 6/15 vegetative parts 7.9 7.4 ---- ---- ---- ---- flower ---- ---- 8.0 12.3 ---- ---- pod ---- ---- ---- ---- 9.0 9.0
Broom snakeweed provides cover for many small birds and mammals. Larger plants provide resting sites for black-tailed jackrabbits in New Mexico . Broom snakeweed also provides black-tailed jackrabbits with protective cover against weather and predators such as coyotes on heavily grazed ranges of New Mexico . In some areas, broom snakeweed serves as good cover for both Gambel's and scaled quail [37,107]. In Oregon, the Columbia Basin burrowing owl selected broom snakeweed habitat for nesting . Cover value is rated as follows :
MT ND UT Pronghorn ---- ---- poor Elk poor ---- poor Mule deer ---- fair ---- White-tailed deer ---- poor ---- Small mammals poor ---- ---- Small nongame birds ---- ---- fair Upland game birds ---- ---- fair Waterfowl ---- ---- poor
Under natural conditions broom snakeweed quickly invades disturbed sites and can minimize soil erosion . It reportedly stabilizes loose wind-blown soils in mesquite (Prosopis spp.) sand dunes . Broom snakeweed is rated as low to moderate in both long- and short-term rehabilitation potential .
Plants may be transplanted or established through seed. Broom snakeweed is well adapted to planting in pinyon-juniper, big sagebrush, northern desert shrub, and southern desert shrub communities .
Some Native American peoples traditionally used broom snakeweed to construct brooms and as a treatment for indigestion .
Increases in broom snakeweed may be due to livestock grazing, drought, weather, or fire suppression . Broom snakeweed quickly invades overgrazed rangeland. Cattle sometimes leave broom snakeweed almost untouched while grazing grasses to within 0.5 inch (1.27 cm) of the soil surface . An abundance of this shrub is considered by some authorities as an indicator of range deterioration . Many researchers believe that broom snakeweed may be reduced and species such as blue grama increased by protection from grazing. Grass production increased from 976 lbs/acre to 2,024 lbs/acre during the first year after complete removal of broom snakeweed in Texas . However, increases in broom snakeweed may be due to climatic fluctuations rather than overgrazing [15,49]. West and Tueller  maintain that climatic factors are more important than grazing in determining the extent of broom snakeweed populations.
Broom snakeweed populations fluctuate in response to annual moisture patterns, with rapid increases commonly occurring after drought periods . This plant apparently exhibits only a slight response to late-season irrigation .
The root system of broom snakeweed occurs at approximately the same soil depth as do the roots of many perennial grasses . Competition for water and nutrients is suspected. Broom snakeweed competition can apparently cause decreases in big bluestem (Andropogon gerardii) and blue grama. However, bottlebrush squirreltail (Elymus elymoides) and black grama appear to be unaffected by the presence of broom snakeweed .
Broom snakeweed can be difficult to kill with herbicides, and opinions vary on the optimum time to spray. Clary and others  noted erratic results from herbicides such as tebuthiuron in the Intermountain region. Stands were often reduced by applications of pelleted tebuthiuron, but reestablishment sometimes compensated for the loss of the original plants. Detailed information on the chemical control of broom snakeweed is available [17,19,35,66,91]. In cases where application of herbicide is effective, broom snakeweed populations are controlled for up to 5 years, although grazing practices and fall and winter precipitation received after application can also influence results. In some cases, fire can be used in combination with herbicides to extend the longevity of chemical treatment to beyond 5-7 years .
Mechanical control is generally ineffective in controlling broom snakeweed . Hoeing the plants just below the soil surface can be effective but is difficult or impractical in stony ground . In Arizona, chaining resulted in increases in broom snakeweed and harrowing in central Arizona reduced populations by only 5 to 10% .
Broom snakeweed is susceptible to severe damage by the round-headed borer (Crossidius pulchellus) and mealybugs (Chorizococcus spp.). These insects were believed to be the major factor causing a broom snakeweed die-off in Texas and New Mexico during a particularly dry summer. Eighty-two percent of the mortality was attributed to insects, while the other 18% was thought to be drought-induced .
Broom snakeweed is a bushy, short-lived, native, perennial shrub or subshrub that grows from 8 to 28 inches (20-70 cm) in height [1,43,62,95,71]. Slender, erect, herbaceous branches arise from a woody crown and stem base . Brittle, herbaceous shoots die back during dormancy but can persist throughout the winter [91,97]. Broom snakeweed produces a deep, woody taproot during the first year of growth, and numerous, extensive lateral roots develop as the plant matures .
High water use efficiency and a high degree of drought tolerance enable broom snakeweed to survive on arid or semi-arid sites . Plants are reportedly allelopathic . Yellow flowers are borne in small, finely hairy achenes . Fruit is oval and covered with chaffy scales . Maximum life span is approximately 20 years .
Flowers of broom snakeweed are pollinated by various insects . Regeneration of broom snakeweed, a cool-season germinator, is primarily through light, wind-dispersed seed [60,111]. However, most ripe seeds fall beneath the parent plant, and seed dispersal is described as "inefficient.". Some seeds remain in the dried capitula for several months before dispersal . Broom snakeweed produces sufficient viable seed to ensure the development of abundant seedlings during good years . Studies indicate that a single plant is capable of producing more than 9,000 to 10,000 seeds annually. Most germination and seedling establishment takes place in winter and spring .
Under laboratory conditions seeds have remained viable for at least 2 years . Osman and Pieper  report that seed can remain viable in the soil for "a considerable period of time." Seeds can remain viable in the soil for at least several years [65,85]. Broom snakeweed can mature and set seed within one to two years .
Most seed is dormant at maturity and requires a 4- to 6-month afterripening period before germination can proceed. After 6 months of afterripening, broom snakeweed germinated best at temperatures of 59 degrees Fahrenheit (15 degrees C) and 86 degrees Fahrenheit (30 degrees C). Light enhances germination of afterripened seed, which suggests that germination may be favored at or near the soil surface .
Broom snakeweed occurs on rocky plains, dry foothills, ridgetops, and mountain slopes, and in semi-desert valleys of the Great Plains and Rocky Mountains . It exhibits wide ecological amplitude  and occurs in a variety of communities including pinyon-juniper woodlands, desert shrublands, and sagebrush-grasslands.
Broom snakeweed occurs on a wide range of soil types including dry, well-drained, sandy, gravelly, or clayey loams and heavy clays. Growth is reportedly best on moderately rich limestone, clay loams of broad alluvial slopes, and shallow, rocky, or sandy soil. Growth is generally poor on saline or alkaline soils .
Generalized elevational ranges of broom snakeweed are as follows :3,700-10,000 feet (1,129-3,050 m) in CO
Broom snakeweed rapidly invades disturbed sites and can dominate early successional stages of many communities . Broom snakeweed commonly colonizes burned big sagebrush communities in parts of the Great Basin . It can compete successfully with many grasses, but is unable to out-compete other perennial shrubs and gradually declines as shrubs increase [60,62].
Neuenschwander  reports highest frequencies of broom snakeweed on 22-year old burns in west-central Utah. Although it persists
in some mid to late seral communities , it is generally poorly represented in climax stands. On west-central Utah, broom snakeweed populations declined gradually in the first 50 years after disturbance . On 100 year-old burns, broom snakeweed was reduced to less than 10% frequency . The following generalized successional pattern for mixed plains communities of northeastern Colorado includes broom snakeweed :
1) initial stage
2) forb stage (9 years after disturbance)
3) short-lived perennial grass stage (14 years after disturbance)
4) Aristida spp. stage (broom snakeweed is present, particularly on ant mounds) (20 years after disturbance)
5) mixed prairie association (40 years after disturbance)
In mesquite (Prosopis glandulosa) communities of the Southwest, succession proceeds as follows :
1) annual grasses and forbs; short-lived perennials
2) some perennial grasses and forbs; broom snakeweed
3) broom snakeweed assumes dominance
4) mesquite dominates the site
Costello  reports that deep-rooted species such as broom snakeweed may appear earlier in succession and may persist longer in bottomlands than on upland sites.
In presettlement big sagebrush communities of southern Idaho, broom snakeweed replaced big sagebrush after fire along with rabbitbrush and horsebrush. After the introduction of exotic annuals, the pattern changed. Russian thistle now initially colonizes burned big sagebrush sites followed by mustard and cheatgrass .
Four main phenological stages occur in broom snakeweed: perennating bud stage in November and December, vegetative growth stage from late January through August, flower bud development in August and November, and flowering stage . Annual growth of broom snakeweed begins in early spring as green herbaceous shoots sprout from the base of the plant. Elongation of the stems and new leaves may begin as early as late January to March . Most vegetative development occurs during the spring and early summer when moisture availability peaks in many locations . In New Mexico, new branches and leaves develop rapidly in July and August . Lower temperatures may limit growth after mid-October in many parts of the Southwest . In south Texas, mature vegetative phenological state generally extends from June to September when maximum canopy dimension is reached [29,65].
Plants generally become dormant after completion of the annual growth cycle, but in some parts of the southwest, plants can remain green if soil water is adequate during the winter . During winter dormancy, stems remain but become brown and die back to near the base of the plant . Carbohydrate storage typically increases during the fall after flowering . Flowering is strongly influenced by available soil moisture, and may be delayed or prolonged during wet years . During dry years both flowering and carbohydrate accumulation may begin earlier . Mature plants may bloom for up to 2 months in wet years. In dry years, or when plants are older, flowering periods may be as short as 2 to 3 weeks . In New Mexico flowering begins in late August with seed set in early November . General flowering dates are as follows :
State Beginning of Flowering End of Flowering CO July October MT July September ND July September UT July September WY May SeptemberSpecific details were reported in a North Dakota study from 1979 to 1984 :
earliest first bloom 7/08/80 latest first bloom 8/15/79 median date of first 10 plants with flowers 7/26 median date of full flowering 8/05 median date when flowering 95% complete 9/05 length of flowering period 45 daysSeed matures in September and October . Growth of perennating buds usually begins in November and December immediately after seed set. At this time leaves change color from green to pale yellow or brown and are shed .
Broom snakeweed, a weak-sprouting perennial, is severely damaged by fire . Plants sometimes sprout but are more typically killed by fire . Reestablishment proceeds rapidly through light, wind-dispersed seed from adjacent unburned areas . The density of broom snakeweed often increases after fire [16,71]. Gatewood  reports that seeds can remain viable in the soil, unharmed by fire, and can germinate immediately after fire or in subsequent years.
The range of fire intervals reported for some species that dominate communities where broom snakeweed occurs are listed below. To learn more about the fire regimes in those communities and others listed below refer to the FEIS summary for those species, under “Fire Ecology or Adaptations.”
ponderosa pine (Pinus ponderosa) 2 to 42 years Mexican pinyon (P. cembroides) 20 to 70 years oneseed juniper (Juniperus monosperma) big sagebrush (Artemisia tridentata) creosotebush (Larrea tridentata) galleta (Hilaria jamesii) blue grama (Bouteloua gracilis) mesquite (Prosopis glandulosa)
Small shrub, adventitious-bud root crown
Initial-offsite colonizer (off-site, initial community)
FIRE REGIMES: Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
Broom snakeweed is a fire-intolerant species that is severely harmed or, more often, killed by fire [45,78]. Broom snakeweed may be completely removed from an area immediately after fire . In some instances, portions of plants survive despite serious damage .
Broom snakeweed is highly combustible when ignited . In the spring, numerous dried flowers and supporting branches from the previous year are readily consumed by fire if there is sufficient fine fuel to move the fire from plant to plant .
Slow, hot fires create a longer duration of heat release which results in greater broom snakeweed mortality. Following fire in New Mexico, McDaniels and others  observed that fires with duration of heat exceeding 140 degrees Fahrenheit (60 oC) longer than 45 seconds reduced broom snakeweed by at least 70%; fires with durations less than 45 seconds gave highly variable results.
In west-central Kansas, broom snakeweed is severely harmed by spring fires .
Although usually killed by fire, plants occasionally sprout . If the entire crown is not consumed, plants may produce shoots from undamaged primordial buds located on lower stems . Reestablishment generally proceeds rapidly through large numbers of light, wind-dispersed seed [69,111].
Fall fires may result in higher broom snakeweed mortality than spring fires. Fall prescribed burning in a basin big sagebrush community in east-central Oregon eliminated broom snakeweed from study plots in postfire year 1 and 2. Spring burning reduced broom snakeweed density relative to the control, but had no significant effect on broom snakeweed frequency . See the Research Project Summary of this study for more information on fire effects on broom snakeweed and 60 additional woody plant, grass, and forb species.
Recovery time of green rabbitbrush may vary with fire severity and season of burning but is generally rapid. In many parts of the Great Basin, broom snakeweed appears in abundance soon after severe fires in sagebrush communities . After spring burns in northern mixed grass prairies, both increases and decreases in broom snakeweed have been reported .
Burning in southern Arizona reduced broom snakeweed cover from 0.66 plants/m2 to 0.13 plants/m2 2 years after fire . Following spring burns in New Mexico, most plants that survived burning (94%) produced shoots from the basal area at or near the surface . After a southern Arizona burn at the beginning of the wet season, broom snakeweed was reduced by 95%. Following April and June burns on blue grama ranges of south-central New Mexico, the cover of broom snakeweed was reduced by 45% and 96% respectively .
In most of the Great Basin, broom snakeweed generally appears by the sixth year following fire if present in adjacent unburned areas . Because of its ability to reestablish rapidly, broom snakeweed often assumes dominance on recently burned Utah sites with cheatgrass (Bromus tectorum) and rabbitbrush (Chrysothamnus spp.) . Some areas develop nearly pure stands of broom snakeweed within 5 to 10 years, although in other locations plants may not dominate the site for up to 25 years [106,108]. Increases in broom snakeweed cover can be dramatic. In a Utah cheatgrass-sand dropseed-red threeawn (Aristida purpurea) community, only minor amounts of broom snakeweed were present prior to a summer wildfire. However, within 5 years after fire, broom snakeweed accounted for 31 percent of the perennial cover. Changes in cover and composition were documented as follows :
(area burned in 1956)
1955 1957 1958 1960 1961
foliage cover 0.6 trace 0.9 6.1 5.9
% composition 0.8 trace 1.2 7.2 7.0
Broom snakeweed was present in 8 of 9 burn age classes in Utah, with peak frequencies occurring on 22-year-old burns in big sagebrush or Utah juniper (J. osteosperma) communities. Broom snakeweed populations declined gradually for 50 years, with frequencies of less than 10 percent reported on burns of 100 years or older . I
In some areas fire can be used to control broom snakeweed during wet weather cycles . Everitt and others  report that broom snakeweed can be controlled by fire during certain phenological stages. In southern Arizona, plants were most vulnerable when burned in October, April, and June . Even cool fires can be effective in controlling broom snakeweed  so long as fuel loadings are sufficient to carry fire . Gatewood  observed that the primary limitation to burning in broom snakeweed communities is inadequate fine fuel. Often dense stands of broom snakeweed (with essentially no grass) do not carry a fire well except under hazardous burning conditions (high air temperatures, high winds, and low relative humidities).
Most important variables in determining the success of a burn in broom snakeweed are litter fuel loading and fine fuel loading. Gatewood  reported that burn cover did not exceed 60% where fine fuel amounts totaled less than 600 kg/ha, where litter fuel was less than 1,200 kg/ha and where combined amounts total less than 1700 kg/ha. Litter moisture, fine fuel in canopy, temperature, and relative humidity are also important variables.
Gatewood  suggests that blacklines can be burned when the following conditions are met: 1) litter moisture is 3-4.5%, 2) fine fuel moisture is less than 20%, 3) relative humidity ranges from 20-45%, 4) temperature is 75-90 degrees Fahrenheit (24-32 oC), and windspeed is 5-9 miles per hour (8-15 km/hr). Prescribed fire should occur as close to the end of the dry season as possible or before vegetation greens up. Spring burns will kill any broom snakeweed seedlings that germinated during the winter. If precipitation has been below normal during previous growing seasons and if drought continues through fall and winter, Gatewood  recommends avoiding prescribed fire in broom snakeweed communities due to poor fire spread.
Once an area has been burned, Gatewood  notes that grazing should be discontinued until recovery has occurred (generally one growing season in normal to wet years, and two or more growing seasons in dry years). Grazing should be deferred until after fall freezes in areas burned in early spring. Because seeds remain viable in the soil, it may be necessary to burn at 5 to 10 year intervals to reduce broom snakeweed populations.
Tirmenstein, D., compiler. 1999. Controlling broom snakeweed with fire in New Mexico. In: Gutierrezia sarothrae. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ .
McDaniel, K. C.; Hart, C. R.; Carroll, D. B. 1997. Broom snakeweed control with fire on New Mexico blue grama rangeland. Journal of Range Management. 50(6): 652-659. .
Spring (March-April)/not specified Summer (June-July)/not specified
Burns were located near Corona, in central New Mexico.
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).
Spring - broom snakeweed was in bud stage with little green foliage.
Summer - broom snakeweed was in active growth phase.
Average annual precipitation - 397 mm
(with >1/2 received during local July-Sept. thunderstorms)
Terrain - level
Elevation - 1,870 m
Soils - shallow loam
Fine fuels biomass consists mainly of graminoids which become limited during periods of low rainfall, excessive grazing, or interference from broom snakeweed.
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
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%.
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.
Areas with excessive amounts of broom snakeweed (>500 kg/ha) and low fine fuel biomass (350 kg/ha) are not suited for prescribed fire.
The following guidelines are recommended for prescribed burns to control broom snakeweed in blue grama grasslands:
Air temperature 22-28 oC
Relative humidity 10-20%
Soil moisture 3-10%
Wind (from SW) 3-8 m/s
Fine fuel moisture less than 15%
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.
Tirmenstein, D., compiler. 1999. Spring and fall prescribed burning of broom snakeweed in basin big sagebrush in east-central Oregon. In: Gutierrezia sarothrae. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].
Sapsis, David B. 1990. Ecological effects of spring and fall prescribed burning on basin big sagebrush/Idaho fescue--bluebunch wheatgrass communities. Corvallis, OR: Oregon State University. 105 p. Thesis. .
Fall (9/25/87)/not specified
Spring (5/24/88)/ not specified
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.
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).
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)
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
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
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