• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

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 [63]. 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 [14].

High water use efficiency and a high degree of drought tolerance enable broom snakeweed to survive on arid or semi-arid sites [101]. Plants are reportedly allelopathic [61]. Yellow flowers are borne in small, finely hairy achenes [97]. Fruit is oval and covered with chaffy scales [105]. Maximum life span is approximately 20 years [8].

RAUNKIAER LIFE FORM:

Phanerophyte

REGENERATION PROCESSES:

Flowers of broom snakeweed are pollinated by various insects [61]. 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 [61]. Broom snakeweed produces sufficient viable seed to ensure the development of abundant seedlings during good years [14]. 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 [92].

Under laboratory conditions seeds have remained viable for at least 2 years [61]. Osman and Pieper [75] 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 [77].

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 [61].

Broom snakeweed sprouts weakly following fire or other disturbance [74,111]. Branches of mature plants occasionally produce adventitious roots when partially covered with sand [14]. 

SITE CHARACTERISTICS:

Broom snakeweed occurs on rocky plains, dry foothills, ridgetops, and mountain slopes, and in semi-desert valleys of the Great Plains and Rocky Mountains [62]. It exhibits wide ecological amplitude [71] 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 [97].

Generalized elevational ranges of broom snakeweed are as follows [26]:

     from   3,700-10,000 feet (1,129-3,050 m) in CO
            2,400-5,700 feet (732-1,739 m) in MT
            4,300-9,500 feet (1,312-2,898 m) in UT
            3,700-8,300 feet (1,129-2,532 m) in WY
 

SUCCESSIONAL STATUS:

Broom snakeweed rapidly invades disturbed sites and can dominate early successional stages of many communities [62]. Broom snakeweed commonly colonizes burned big sagebrush communities in parts of the Great Basin [110]. 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 [74] 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 [32], it is generally poorly represented in climax stands. On west-central Utah, broom snakeweed populations declined gradually in the first 50 years after disturbance [5]. On 100 year-old burns, broom snakeweed was reduced to less than 10% frequency [5]. The following generalized successional pattern for mixed plains communities of northeastern Colorado includes broom snakeweed [18]:

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 [28]:

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 [18] 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 [109].

SEASONAL DEVELOPMENT:

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 [34]. 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 [67]. Most vegetative development occurs during the spring and early summer when moisture availability peaks in many locations [91]. In New Mexico, new branches and leaves develop rapidly in July and August [65]. Lower temperatures may limit growth after mid-October in many parts of the Southwest [14]. 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 [92]. During winter dormancy, stems remain but become brown and die back to near the base of the plant [97]. Carbohydrate storage typically increases during the fall after flowering [91]. Flowering is strongly influenced by available soil moisture, and may be delayed or prolonged during wet years [19]. During dry years both flowering and carbohydrate accumulation may begin earlier [91]. 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 [92]. In New Mexico flowering begins in late August with seed set in early November [65]. General flowering dates are as follows [26]:

  State          Beginning of Flowering      End of Flowering

    CO                     July                  October
    MT                     July                  September
    ND                     July                  September
    UT                     July                  September
    WY                     May                   September
 

        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 days
 

Related categories for SPECIES: Gutierrezia sarothrae | Broom Snakeweed