Index of Species Information

SPECIES:  Gutierrezia microcephala


SPECIES: Gutierrezia microcephala
AUTHORSHIP AND CITATION : Carey, Jennifer H. 1994. Gutierrezia microcephala. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. ABBREVIATION : GUTMIC SYNONYMS : Xanthocephalum microcephalum (DC.) Shinners [31,40] SCS PLANT CODE : GUMI COMMON NAMES : small-head snakeweed perennial snakeweed threadleaf snakeweed TAXONOMY : The currently accepted scientific name for small-head snakeweed is Gutierrezia microcephala (DC.) Gray (Asteraceae) [16,18,27,31,39,40]. There are no currently accepted infrataxa. This report refers to small-head snakeweed and its more common relative, broom snakeweed (Gutierrezia sarothrae) together as perennial snakeweeds. LIFE FORM : Shrub FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Gutierrezia microcephala
GENERAL DISTRIBUTION : Small-head snakeweed occurs in the Chihuahuan, Sonoran, Mojave, and Great Basin deserts of the southwestern United States and northern Mexico. It occurs from southwestern Texas; north to extreme southwestern Colorado and south-central Utah; west to southern California; and south to the Mexican states of Sonora, Chihuahua, and Coahuila [16,18,27,31,39,40]. ECOSYSTEMS : FRES21 Ponderosa pine FRES30 Desert shrub FRES33 Southwestern shrubsteppe FRES35 Pinyon - juniper FRES40 Desert grasslands STATES : AZ CA CO NV NM TX UT MEXICO BLM PHYSIOGRAPHIC REGIONS : 3 Southern Pacific Border 6 Upper Basin and Range 7 Lower Basin and Range 12 Colorado Plateau 13 Rocky Mountain Piedmont KUCHLER PLANT ASSOCIATIONS : K019 Arizona pine forest K023 Juniper - pinyon woodland K039 Blackbrush K040 Saltbush - greasewood K053 Grama - galleta steppe K054 Grama - tobosa prairie K057 Galleta - three-awn shrubsteppe K058 Grama - tobosa shrubsteppe K059 Trans-Pecos shrub savanna SAF COVER TYPES : NO-ENTRY SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Small-head snakeweed occurs in arid grassland and desert shrub communities. In an arid grassland in New Mexico, small-head snakeweed occurs with galleta (Hilaria jamesii), sand dropseed (Sporobolus cryptandrus), black grama (Bouteloua eriopoda), and ring muhly (Muhlenbergia torreyi) [29]. Other desert associates include Joshua tree (Yucca brevifolia), Nevada ephedra (Ephedra nevadensis), cholla cactus (Opuntia spp.), and Mojave desertrue (Thamnosma montana) [3,4].


SPECIES: Gutierrezia microcephala
IMPORTANCE TO LIVESTOCK AND WILDLIFE : Small-head snakeweed is poisonous to livestock, especially when it is growing on sandy soils. It contains saponins and other chemicals that cause abortions in cattle. Clinical signs of small-head snakeweed poisoning are described [24,34]. Small-head snakeweed has very little known value to wildlife [9]. It may provide cover for small animals, and wildlife may eat the seeds. PALATABILITY : Perennial snakeweeds are generally unpalatable to cattle [12,25] except in early spring when other forage is lacking [34]. NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : NO-ENTRY OTHER MANAGEMENT CONSIDERATIONS : Small-head snakeweed invades and is an indicator of overgrazed and disturbed rangelands [9,31]. Once established, small-head snakeweed biomass can exceed 1,000 pounds per acre and reduce grass production to less than 100 pounds per acre [33]. In 1987 approximately 22 percent of Texas rangelands were infested with perennial snakeweeds [26]. Small-head snakeweed persists after grazing ceases [30] so it may threaten diversity in native plant communities as well as decrease forage values. Various herbicide application techniques have been tested on perennial snakeweeds. Picloram and triclopyr give satisfactory control [21]. Picloram is most effective at controlling small-head snakeweed when applied after fall flowering but before new terminal growth begins. Control lasts at least 5 to 7 years under proper grazing management [33]. The percent canopy reduction of small-head snakeweed was substantially greater when herbicide was applied during the spring of an above-average rainfall year than in a drought year [26]. Biological control of perennial snakeweeds is currently under study [9,10]. A root-boring weevil from Argentina, closely related to the native cerambycid root borer (Crossidius pulchellus), was released in the late 1980s in Texas and New Mexico; the release marks the first attempt to control a native weed with a foreign insect [10]. The native cerambycid root borer is not useful for biological control because it feeds only on large, mature plants, and damage is sporadic [10,30].


SPECIES: Gutierrezia microcephala
GENERAL BOTANICAL CHARACTERISTICS : Small-head snakeweed is a small, native, resinous, perennial desert subshrub that is typically less than 1.6 feet (0.5 m) in height and less than 3.3 feet (1 m) in canopy diameter. It has many erect herbaceous stems which arise from woody basal stems and die back annually [16,27,30,40]. The herbaceous stems are photosynthetic, giving the plant a high photosynthetic capacity [24]. A mature plant with an 8- to 12-inch (20-30 cm) canopy diameter has 100 to 200 photosynthetic stems [30]. The seedling taproot becomes more extensive and diffuse with age [24]. Root length of mature plants averages 6.9 inches (17.4 cm) [25]. Small-head snakeweed generally lives less than one decade; maximum age observed in a New Mexico grassland was 18 years [30]. Small-head snakeweed exhibits some degree of summer deciduousness. In the Mojave Desert in western Arizona, total small-head snakeweed canopy in early August was 54 percent of the maximum biomass observed in spring [8]. RAUNKIAER LIFE FORM : Chamaephyte Phanerophyte REGENERATION PROCESSES : Small-head snakeweed produces many seeds [30,33]. Wind dispersal of seeds is inefficient because of a highly reduced pappus, so most seeds fall within a few meters of the parent plant [30]. Seeds are dormant and require a 4- to 6-month afterripening period. After 6 months, maximum germination occurs at a constant temperature from 59 to 77 degrees Fahrenheit (15-25 deg C) with an 8-hour light period. Light enhances germination, suggesting that germination is favored at or near the soil surface [22]. In a New Mexico grassland, seeds germinated abundantly where the established vegetation had been experimentally removed [30]. Germination is also enhanced by winter and spring precipitation [29]. Seedlings produce a single stem and a taproot. A yearling has three to four stems. Several years are required before seeds are produced [30]. The duration of small-head snakeweed seed viability in soil is unknown [25]. Parker [30] found an average of 24.2 viable seeds per square meter in the soil of an arid grassland site in New Mexico. Seedling abundance was not noticeably depressed in the spring following a year in which insect herbivory destroyed the seed crop [30]. Parker [30] found considerable year-to-year fluctuation in plant recruitment. Small-head snakeweed is vulnerable to local extinction because seedlings frequently succumb to drought, grasshopper defoliation, and competition from grasses [30]. In an arid New Mexico grassland, seedling survival was five times greater where competing vegetation had been removed than on undisturbed sites. In a year of abundant grasshoppers (Hesperotettix viridis), predation on threadleaf snakeweed seedlings was reduced when mature small-head snakeweed plants were nearby because the grasshoppers generally hopped from one mature small-head snakeweed canopy to another and rarely moved among seedlings at ground level [29]. According to Mayeux and Leotta [22], small-head snakeweed reproduces solely by seed. One reference from a study in New Mexico described a very low rate of sprouting from the root crown after mature plants were clipped to ground level [29]. SITE CHARACTERISTICS : Small-head snakeweed occurs in desert climates [8]. In southwestern Utah, small-head snakeweed is preferentially associated with xeroriparian sites which have higher annual moisture than uplands but running water only on infrequent occasions [23]. It primarily occurs on well-drained, sandy, gravelly, or rocky soils [4,16,28,41]. It is often found in washes or on adjacent slopes [8]. Small-head snakeweed often predominates on southern exposures with shallow rocky soils where grasses are not well established [4]. Elevational ranges by state are as follows: Arizona 3,500 to 6,500 feet (1,100-2,000 m) [18] California 5,900 to 8,200 feet (1,800-2,500 m) [16] Colorado 4,000 to 8,000 feet (1,200-2,400 m) [12] Texas 2,500 to 6,000 feet (760-1,800 m) [31] Utah 2,800 to 6,000 feet (850-1,830 m) [40] Although the ranges of the two perennial snakeweeds overlap, they appear to occupy slightly different niches. Small-head snakeweed was more prevalent than broom snakeweed on drier upper slopes along a vegetation transect in the Chihuahuan Desert, New Mexico [41]. However, in southwestern Utah, small-head snakeweed occupied the lower slope and floodplain while broom snakeweed occupied the upper slope and ridgetop [3]. SUCCESSIONAL STATUS : Small-head snakeweed is probably intolerant of shade since it rarely occurs in the presence of a woody overstory [25]. It pioneers on disturbed sites and overgrazed rangeland [28,20,31,38]. In San Bernardino County, California, small-head snakeweed was present in low numbers on a pipeline construction zone 12 years after the disturbance [38]. Perennial snakeweed populations are often cyclic, dying back when conditions for seedling establishment are unfavorable and then reappearing when conditions are favorable [24]. Prolific seed production and buried seeds permit opportunistic seedling recruitment during favorable periods. Once established on a site, threadleaf snakeweed may persist numerous generations despite a short life span, poor seedling recruitment during some years, and intense competition from grasses [30]. SEASONAL DEVELOPMENT : New terminal growth begins on basal stems from January through March. Flowering is initiated in the spring and early summer, but plants become dormant during summer drought and do not bloom until late summer or fall. Twig dieback occurs in late fall after flowering [8,33]. Flowering phenology depends on yearly climatic conditions; blooms last longer in wet years [33]. Germination occurs in early spring [30].


SPECIES: Gutierrezia microcephala
FIRE ECOLOGY OR ADAPTATIONS : Desert shrub communities in which small-head snakeweed occurs do not burn regularly. Fire frequency depends on the continuity of fuels, which may only be adequate for fire after wet years. Fire in blackbrush (Coleogyne ramosissima) communities is rare but does occur with high temperatures, high wind velocity, and low relative humidity. Arid grasslands burn more regularly than desert shrub communities. Where livestock grazing has reduced grass cover, however, fire frequency has decreased. Woody species have increased on grasslands with fire suppression and heavy grazing [17,42]. Small-head snakeweed probably resists fire by regenerating from buried seed and by surviving in unburned patches. POSTFIRE REGENERATION STRATEGY : Ground residual colonizer (on-site, initial community) Secondary colonizer - off-site seed


SPECIES: Gutierrezia microcephala
IMMEDIATE FIRE EFFECT ON PLANT : Fire kills or severely damages perennial snakeweeds [15,20,42,43,44]. Small-head snakeweed probably burns readily because it is resinous. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Small-head snakeweed may colonize recently burned sites from buried seed or seed from adjacent unburned sites if moisture conditions are favorable and grass competition is not severe. Although information pertaining to the response of small-head snakeweed to fire is lacking in the literature, the presence of threadleaf snakeweed on unburned and burned sites has been documented. In New Mexico, small-head snakeweed had a density of 0.5 to 1.0 plant per square meter on an arid grassland that had not experienced fire for at least 30 years [30]. Small-head snakeweed was present on some burn sites but not others in blackbrush communities in southwestern Utah. The vegetation was examined on eight sites, each having been burned once in the past 37 years. Prefire species cover and frequency were not known, and site histories differed. Small-head snakeweed was not present on sites burned 1, 2, 6, and 37 years previously. It was present on sites burned 12, 17, and 19.5 years previously, at absolute covers of 0.3, 10.2, and 24.8 percent, respectively [5]. The authors did not discuss reasons for the variable presence of threadleaf snakeweed. The 2-, 6-, and 12-year-old burns had been seeded with grasses so colonization by small-head snakeweed may have been prevented or delayed by grass competition. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Prescribed burning is frequently used as a management tool to increase forage on rangelands [5]. Historically, fire played an important role in controlling woody species [20,42]. However, prescribed burning for control of perennial snakeweeds has met with mixed success [24,42]. Wright and Bailey [42] suggested that fire can be used to control perennial snakeweeds during wet weather cycles when the grasses will not be severely damaged. The individual grass species and their ability to recover from fire should be considered when prescribed burning for perennial snakeweed control [42]. Prescribed burning of perennial snakeweeds is limited by inadequate fine fuel. In a study of a broom snakeweed-infested grassland in southeastern New Mexico, the area burned by spring prescribed fires did not exceed 60 percent unless the fine fuel loading exceeded 534 pounds per acre and the litter fuel exceeded 1,000 pounds per acre, or the two fuels combined exceeded 1,500 pounds per acre. If there is enough fuel, a headfire is effective if the following criteria are met: litter moisture is 3 to 4.5 percent, fine fuel moisture is less than 20 percent, relative humidity is less than 20 percent, ambient temperature is between 75 and 90 degrees Fahrenheit (24-32 deg C), and the wind speed is 8 to 15 miles per hour [15].


SPECIES: Gutierrezia microcephala
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Durant; Sanderson, Stewart C. 1992. A comparison between xeroriparian and upland vegetation of Beaver Dam Slope, Utah, as desert tortoise habitat. In: Clary, Warren P.; McArthur, E. Durant; Bedunah, Don; Wambolt, Carl L., compilers. Proceedings--symposium on ecology and management of riparian shrub communities; 1991 May 29-31; Sun Valley, ID. Gen. Tech. Rep. INT-289. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 25-31. [19091] 24. McDaniel, K. C.; Briede, J. W.; Torell, L. Allen. 1991. Classification, ecology, and economics of perennial snakeweed. In: James, Lynn F.; Evans, John O.; Ralphs, Michael H.; Child, R. Dennis, eds. Noxious range weeds. Westview Special Studies in Agri. Science and Policy. Boulder, CO: Westview Press: 210-219. [23550] 25. McDaniel, Kirk C.; Pieper, Rex D.; Loomis, Lyn E.; Osman, Abdelgader A. 1984. Taxonomy and ecology of perennial snakeweeds in New Mexico. Bulletin 711. 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