Cheatgrass

Appearance

''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 .

The stems are smooth and slender. The leaves are hairy and have sheaths that are separate except at the node where the leaf attaches to the stem. It typically reaches 40–90 centimetres tall, though plants as small as 2.5 centimetres 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 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 to a depth of 70 centimetres , reducing competition from other species.There is a positive correlation between native vegetation communities and biological soil crust . BSC is composed of cyanobacteria, algae, lichens, and mosses living on the soil. In arid regions BSCs colonize the spaces in-between plants, increase the biodiversity of the area, are often the dominant cover, and are vital in ecosystem function. In addition to providing erosion control, BSC is vital for nutrient cycling and carbon fixing. Fire and trampling by cattle are the major threats to the BSC communities, and once disturbed it can take decades to centuries for BSC to reform.  A decline in the health of the BSC community serves as an early warning indicator for ''Bromus tectorum'' invasion. If the BSC community is healthy then it will impede ''B. tectorum'' germination and reduce the likelihood of invasion. However, if there is a disturbance in the biological soil crust and downy brome is able to establish, then ''B. tectorum'' will impede the recovery of the BSC community.

Native perennial grasses have roots that often reach four feet into the soil. These roots provide organic matter, which feeds the soil organisms, who assist in water and nutrient cycling in arid ecosystems and improve soil quality''. Bromus tectorum'' has a shallow spreading root system, which makes it much more efficient at absorbing moisture from light precipitation episodes and disrupts nutrient cycling. Several studies have shown that native plant biomass, especially that of bunchgrasses, negatively effects ''B. tectorum'' cover and biomass, suggesting that a diverse native perennial community will be more resistant to ''B. tectorum'' invasion.

Studies have identified ''Poa secunda, Pseudoroegneria spicata,'' and ''Achnatherum thurberianum'' as key grasses for ''B. tectorum'' resistance. The life strategies of these three grasses differ in such a way that they provide constant interaction and competition with ''B. tectorum.'' ''P. spicata,'' and ''A. thurberianum'' are deep rooted and complete most of their growth in the late spring, and ''P. secunda'' is shallow rooted and completes most of its growth in the late winter and early spring. 

Perennial grass ecosystems are less prone to burning. ''B. tectorum'' has been historically thought to create a positive feedback loop. However, Taylor et al. suggests that fire alone does not promote ''B. tectorum.'' If an area burns the ''B. tectorum'' cover and biomass does not increase as was once thought, but recovers to previous levels. Increased fires because of ''B. tectorum'' may serve to maintain, not increase, the ''B. tectorum'' population by preventing the natives from establishing.

Naming

In the US, it grows on rangelands, pastures, prairies, fields, waste areas, eroded sites, and roadsides. It is much reviled by ranchers and land managers. ''B. tectorum'' seeds are also a critical portion of the diet of the chukar and grey partridge which have been introduced to the US. Intensive sheep browsing of ''B. tectorum'' in early spring has been used as a fire fuels reduction strategy in the hills adjacent to Carson City, Nevada. Because of rangeland fires and the invasion of ''Bromus tectorum'', in 2010 the United States Fish and Wildlife Service considered the possibility of extending the protections of the Endangered Species Act to the greater sage-grouse. The primary focus of Secretarial Order 3336, signed in 2015 in response to the USFWS status review, was to reduce threats greater sage-grouse habitat by reducing the frequency and severity of rangeland fire. Specifically, Secretarial Order 3336 focused on how reducing ''B. tectorum'' could reduce the frequency and extent of rangeland fires. Since the review of the status of the greater sage-grouse by the USFWS in 2010 and the implementation Secretarial Order 3336 in 2015 the bulk of the research focusing on ''B. tectorum'' ecology and control has been completed. 

''B. tectorum'' has demonstrated a quantitative and qualitative response to recent and near-term changes in the concentration of atmospheric carbon dioxide. Laboratory experiments have shown that above-ground biomass increased 1.5–2.7 gram per plant for every 10 part per million increase above the 270 ppm pre-industrial baseline. On the qualitative side, rising carbon dioxide decreased the digestibility and potential decomposition of ''B. tectorum''. In addition to stimulation of biomass, rising carbon dioxide may also increase the above ground retention of ''B. tectorum'' biomass by decreasing removal by animals or bacteria. Ongoing increases in atmospheric carbon dioxide may contribute significantly to ''B. tectorum'' productivity and fuel load with subsequent effects on wildfire frequency and intensity.

''B. tectorum'' has been shown to benefit from endophytic colonization by morels in western North America.    

Status

''Bromus tectorum'' has been introduced to southern Russia, west central Asia, North America, Japan, South Africa, Australia, New Zealand, Iceland, and Greenland. It was first found in the United States in 1861 in New York and Pennsylvania, by 1928 ''B. tectorum'' reached throughout the United States , except for Florida and portions of Alabama, Georgia, South Carolina. ''B. tectorum'' is most abundant in the Great Basin, Columbia Basin, and part of the introduced species that replaced California native plants in the Floristic Province's grasslands and other habitats. In Canada ''B. tectorum'' has been identified as an invasive weed in all provinces, and extremely prevalent in Alberta and British Columbia .

Habitat

''Bromus tectorum'' grows in many climatic areas. It is found primarily in the 150–560 millimetres 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 and slows when temperatures exceed 15 °C .