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

GENERAL BOTANICAL CHARACTERISTICS:

Western wheatgrass is a long-lived, native perennial, cool-season, endomycorrhizal grass [114,115]. It is an aggressive sod-forming grass characterized by an abundance of long, branched rhizomes [10,27]. Rhizomes allow plants to survive moderately severe drought [152]. The erect culms reach 12 to 36 inches (30-90 cm) in height [130].

Rhizomes lie 0.5 to 2 inches (1.3-5 cm) below the soil surface. The highly branched root system may penetrate the soil to a depth of 7 feet (21 m). In the deep rich soils of eastern Nebraska and Kansas, roots may extend as deep as 11.8 feet (3.6 m). Root extensions in more arid eastern Colorado may extend downward to depths of only 4.9 feet (1.5 m) [34]. In dry grasslands of Montana, only 6% of the roots of western wheatgrass were observed in the top 0 to 0.5 inch (0-1 cm) soil layer.

Longevity of western wheatgrass roots was studied by banding roots of plants grown in containers from seed. In the second year 55 and 60% of the banded roots were dead. By the end of the second summer western wheatgrass roots had a survival of 42% [154]. Zhang and Romo [174] report tiller longevity of 2 to 3 years in Saskatchewan.

RAUNKIAER LIFE FORM:

Geophyte

REGENERATION PROCESSES:

Western wheatgrass regenerates vegetatively through rhizomes to form uniform stands [68]. It also spreads via seeds. A limited seed supply usually matures late, but this is offset by reproduction from rootstocks [150]. Stands are slow to develop from seed [27], but once established are vigorous, hardy, and drought resistant. Seeds germinate slowly, but a fairly uniform sod is usually obtained within 2-3 years [10].

Western wheatgrass exhibits a low and much-delayed germination at 66 to 73 degrees Fahrenheit (19-2 ^oC) [26,114,145]. Germination is most successful with alternating temperatures of 59 degrees Fahrenheit (15 ^oC) and 86 degrees Fahrenheit (30 ^oC) [39]. Light does not affect germination [122,141].

Peak germination response for western wheatgrass was 94% at 65 degrees Fahrenheit (18.5 ^oC) for 8 hours and 50 degrees Fahrenheit (10 ^oC) for 16 hours. The mean germination time was 11.8 days. In constant temperature without light, germination percentages decrease [93,122].

SITE CHARACTERISTICS:

Western wheatgrass is drought tolerant, and established stands can survive even extended periods of drought [27,68,130]. It commonly occurs along ephemeral creeks where it grows through thick layers of silt in areas that flood in spring [9,68]. It also grows on well-drained upland sites [130]. Western wheatgrass grows in mesic areas, swales, overflow sites, and subirrigated lowlands. Western wheatgrass is tolerant of periodic flooding, poor drainage, and water tables within 6 inches (15 cm) of the soil surface [27].

Western wheatgrass commonly grows on medium to heavy textured soils [27]. It can grow on even heavy gumbo soils, but does poorly on sand [9,130]. In parts of Colorado, western wheatgrass grows on clayey soils with an average pH of 7.78 [9].Western wheatgrass is highly tolerant of saline to alkali soils [27]. Western wheatgrass is adapted to areas that receive 14 to 35 inches (360-870 mm) of average annual precipitation [130].

Elevational ranges vary as follows [45]:

    3,600 to 10,000 feet (1098-3049 m) in Colorado
    2,400 to  3,600 feet (732-1098 m)  in Montana
    4,200 to  7,500 feet (1280-2677 m) in Utah
    3,400 to  8,200 feet (1037-2500 m) in Wyoming
 

SUCCESSIONAL STATUS:

Western wheatgrass occurs in all seres. It is however, frequently described as a "late successional species" [89,127]. It is present in many climax plant communities [115]. Western wheatgrass increases during secondary succession. Its ability to rapidly reestablish after disturbance is attributed to its rhizomatous growth habit [123]. Samuel and Hart [124] report that it typically appears much earlier and in much greater abundance than other long-lived perennial grasses on disturbed sites in Wyoming.

Western wheatgrass grows in a variety of successional stages in sagebrush (Artemisia spp.) communities. It has been described as a "mid-seral species" in semi-arid sagebrush communities of northwestern Colorado. In these sagebrush communities, annual forbs dominate disturbed sites for the first 2 years after disturbance. By year 3, cheatgrass (Bromus tectorum) typically becomes dominant and perennial grasses such as western wheatgrass become dominant by the 4th year after disturbance [104]. In big sagebrush communities, western wheatgrass may among the earliest species to become prominent following disturbance [19]. In Wyoming big sagebrush communities, western wheatgrass dominates "late intermediate seral stages" in steppe communities [16]. It replaces blue grama in "early intermediate seral stages" and is replaced by big sagebrush later in succession.

Western wheatgrass is common on disturbed sites (abandoned towns) in parts of southwestern Montana [92]. During the drought of the 1930s, western wheatgrass supplanted tall grasses over much of the eastern Kansas prairie [113]. Grasses reverted to the original composition as more "normal" (more moist) conditions returned.

In certain Montana riparian communities, years of heavy grazing can cause cottonwood stands to be replaced by shrub/grass communities dominated by silver sagebrush (Artemisia cana), greasewood (Sarcobatus vermiculatus), and western wheatgrass [70].

SEASONAL DEVELOPMENT:

Western wheatgrass produces best growth in spring. Flowering occurs in June, and seeds ripen in August or September [150]. In South Dakota, vegetative growth typically begins in early June, flowering begins by mid to late June, and seeds shatter by mid-August [85]. Flowering dates by state are as follows [45]:

State   Earliest date observed   Latest date observed
CO      June                     August
MT      June                     August
ND      June                     July
WY      June                     August

Dormancy         5-20 November
Early growth    15-20 April
Rapid growth     1-10 June
Boot stage       1-15 August

Phenology           Range                Average
Growth initiation   March 5-April 26     March 15
Full bloom          June 20-July 20      July 10
Start of seed       July 25-November 20  August 15
  dissemination

In northeastern Colorado, the following phenological development was observed [44]:

Floral buds and open flowers                  Early June
Floral buds, open flowers and ripening fruit  Mid-June
Buds, flowers, green and ripe fruit           Early June
Bud, flowers, green, ripe fruit and 
  dispersing seed                             End of July-Early August

Green and ripe fruit, dispersing seed and
  senescence                                  Early October   

The growth and phenological stages of western wheatgrass plants are inversely related to carbohydrate reserve storage. Lowest root and crown total nonstructural carbohydrate (TNC) levels are reached during the 3rd leaf stage in April. The highest TNC levels occur during the 5th leaf stage in late June and at the end of the growing season, fall quiescence [106]. Seed maturity occurs when water concentrations reach approximately 300 to 350 g/kg (dry weight basis) [17]

Related categories for SPECIES: Pascopyrum smithii | Western Wheatgrass