Bromus tectorum

Bromus tectorum, known as drooping brome or cheatgrass, is a winter annual grass native to Europe, southwestern Asia, and northern Africa, but has become invasive in many other areas. It now is present in most of Europe, southern Russia, Japan, South Africa, Australia, New Zealand, Iceland, Greenland, North America and Asia. In the eastern US B. tectorum is common along roadsides and as a crop weed, but usually does not dominate an ecosystem. It has become a dominant species in the Intermountain West and parts of Canada, and displays especially invasive behavior in the sagebrush steppe ecosystems where it has been listed as a noxious weed. B. tectorum often enters the site in an area that has been disturbed, and then quickly expands into the surrounding area through its rapid growth and prolific seed production. The reduction of native plants and the increased fire frequency caused by B. tectorum prompted the United States Fish and Wildlife Service (USFWS) to examine if the greater sage-grouse needed to be listed as a threatened or endangered species due to habitat destruction. After the review was completed by the USFWS, Secretarial Order 3336 was signed with the goal of reducing the threat of rangeland fires and preserve habitat by reducing downy brome. Research has shown that ecosystems with a healthy biological soil crust and native plant community will be resistant to B. tectorum invasion. In areas where B. tectorum is invasive treatments that are being researched/used by land managers to control B. tectorum include seeding of native plants and non-native bunch-grasses to out compete B. tectorum, herbicides, and prescribed burns. The effectiveness of these treatments is tightly linked to the timing of the water availability at the site. With precipitation shortly after herbicide and seeding treatments increasing the success, and overall high precipitation increases B. tectorum growth, causing the treatment effects to be statistically insignificant. Bromus comes from a Greek word for a type of oat, and tectorum comes from tector which means overlaying and tectum which means roof. Bromus tectorum is a winter annual grass native to Eurasia usually germinating in autumn, overwintering as a seedling, then flowering in the spring or early summer. B. tectorum may be mistaken for a bunchgrass because it may send up shoots that give it the appearance of having a rosette. In areas where it is growing in dense stands the plants will not form this rosette like structures, but instead are single-culmed (stalked). The stems are smooth (glabrous) and slender. The leaves are hairy (pubescent) and have sheaths that are separate except at the node where the leaf attaches to the stem. It typically reaches 40–90 centimetres (16–35 in) tall, though plants as small as 2.5 centimetres (0.98 in) may produce seed. The flowers of B. tectorum are arranged on a drooping panicle with approximately 30 spikelets with awns and five to eight flowers each. It is cleistogamous (self pollinating, non-opening flower) with no evident out-crossing. B. tectorum has a fibrous root system with few main roots that does not reach more than a foot into the soil, and has wide-spreading lateral roots that make it efficient at absorbing moisture from light precipitation episodes. A study showed that it had the capability to reduce soil moisture to the permanent wilting point (minimal soil moisture required for a plant not to wilt) to a depth of 70 centimetres (28 in), reducing competition from other species. Bromus tectorum grows in many climatic areas. It is found primarily in the 150–560 millimetres (5.9–22.0 in) precipitation zone. It will grow in almost any type of soil, including B and C horizons of eroded areas and areas low in nitrogen. B. tectorum is quick to colonize disturbed areas. It is most often found on coarse-textured soils and does not grow well on heavy, dry, and/or saline soils. It grows in a relatively narrow range of soil temperatures; growth starts at 2.0–3.5 °C (35.6–38.3 °F) and slows when temperatures exceed 15 °C (59 °F). The seeds ripen and disperse in the late spring and early summer. They are dispersed by wind, small rodents, or attachment to animal fur, within a week of maturity. They are also moved as a contaminant in hay, grain, straw, and machinery. Bromus tectorum is an abundant seed producer, with a potential in excess of 300 seeds per plant; seed production per plant is dependent on plant density. Under optimal conditions, B. tectorum may produce 450 kg of seed per hectare (400 pounds per acre) with about 330,000 seeds/kg (150,000 seeds/pound). As the seed of B. tectorum ripen the plant goes from green to purple to straw-colored. B. tectorum seeds demonstrate rapid germination as soon as the seed lands in appropriate conditions. If winter rainfall is limiting and germination is inhibited, but spring moisture is adequate, then seeds will germinate in the spring, and the plants will flower that summer. The seeds maintain high viability (ability to germinate under optimal conditions) in dry storage, lasting over 11 years. In the field, under buried conditions, seeds will lose their viability in 2–5 years. Seeds can withstand high soil temperatures, and the primary limit to germination is inadequate moisture. Germination is best in the dark or in diffuse light. They germinate most quickly when covered with soil, but do not need to be in contact with bare soil. Some leaf litter cover will generally improve germination and establishment of seedlings. Seedlings emerge rapidly from the top 2.5 cm (1') of soil, and a few plants emerge from depths of 8 cm (3'), but not from seeds 10 cm (4') below the surface.