''Bromus tectorum'', known as downy brome, drooping brome or cheatgrass, is a winter annual

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...

native to

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, southwestern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

, and northern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, 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 western

Central Asia Central Asia, also known as Middle Asia, is a subregion, region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes t ...

. 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 The Intermountain West, or Intermountain Region, is a geographic and geological region of the Western United States. It is located between the front ranges of the Rocky Mountains on the east and the Cascade Range and Sierra Nevada on the wes ...

and parts of Canada, and displays especially invasive behavior in the

sagebrush steppe Sagebrush steppe is a type of shrub-steppe, a plant community characterized by the presence of shrubs, and usually dominated by sagebrush, any of several species in the genus '' Artemisia''.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 The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...

(USFWS) to examine if the

greater sage-grouse The greater sage-grouse (''Centrocercus urophasianus''), also known as the sagehen, is the largest grouse (a type of bird) in North America. Its range is sagebrush country in the western United States and southern Alberta and Saskatchewan, Canad ...

needed to be listed as a threatened or endangered species due to

habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

. 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 Biological soil crusts are communities of living organisms on the soil surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, ...

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. HAF Transect

Description

''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

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

ing in the spring or early summer. ''B. tectorum'' may be mistaken for a bunchgrass because it may send up

shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the sp ...

s 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 Glabrousness (from the Latin '' glaber'' meaning "bald", "hairless", "shaved", "smooth") is the technical term for a lack of hair, down, setae, trichomes or other such covering. A glabrous surface may be a natural characteristic of all or part of ...

) and slender. The leaves are hairy ( pubescent) and have sheaths that are separate except at the

node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines ...

where the leaf attaches to the stem. It typically reaches tall, though plants as small as may produce seed. The flowers of ''B. tectorum'' are arranged on a drooping panicle with approximately 30

spikelets A spikelet, in botany, describes the typical arrangement of the flowers of grasses, sedges and some other Monocots. Each spikelet has one or more florets. The spikelets are further grouped into panicles or spikes. The part of the spikelet that ...

with awns and five to eight flowers each. It is

cleistogamous Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. Especially well known in peanuts, peas, and pansies, this behavior is most widespread in the grass family. How ...

(self pollinating, non-opening flower) with no evident

out-crossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a usefu ...

. ''B. tectorum'' has a fibrous root system with few main roots that does not reach more than a foot into the

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

, and has wide-spreading lateral roots that make it efficient at absorbing moisture from light

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

episodes. A study showed that it had the capability to reduce soil moisture to the

permanent wilting point Permanent wilting point (PWP) or wilting point (WP) is defined as the minimum amount of water in the soil that the plant requires not to wilt. If the soil water content decreases to this or any lower point a plant wilts and can no longer recover ...

(minimal soil moisture required for a plant not to wilt) to a depth of , reducing

competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indiv ...

from other species.

Habitat

''Bromus tectorum'' grows in many different climates. It is found primarily in the precipitation zone. It will grow in almost any type of soil, including B and C horizons of eroded areas and areas low in

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

. ''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 and slows when temperatures exceed .

Seeds

The

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...

s ripen and disperse in the late spring and early summer. They are dispersed by wind, small

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

s, 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.

Status as an exotic weed

2014-05-29 16 43 23 Cheat grass in Elko, Nevada

''Bromus tectorum'' has been introduced to southern

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

, west central

, North America, Japan,

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

, Australia,

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

, and

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...

. It was first found in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

(where it is known as downy brome or cheatgrass) in 1861 in New York and

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

, and by 1928 ''B. tectorum'' had spread to all parts of the United States (including

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

and

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...

), except for

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

and portions of

Alabama (We dare defend our rights) , anthem = "Alabama" , image_map = Alabama in United States.svg , seat = Montgomery , LargestCity = Huntsville , LargestCounty = Baldwin County , LargestMetro = Greater Birmingham , area_total_km2 = 135,765 ...

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...

, and

South Carolina )'' Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...

. ''B. tectorum'' is most abundant in the Great Basin, Columbia Basin, and is part of the

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...

that replaced California native plants in the

California Floristic Province The California Floristic Province (CFP) is a floristic province with a Mediterranean-type climate located on the Pacific Coast of North America with a distinctive flora similar to other regions with a winter rainfall and summer drought climate ...

grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

s and other

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s. In Canada ''B. tectorum'' has been identified as an invasive weed in all provinces, and is extremely prevalent in Alberta and British Columbia .

Invasive species

In the US, it grows on rangelands,

pasture Pasture (from the Latin ''pastus'', past participle of ''pascere'', "to feed") is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep, or sw ...

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

s, fields, waste areas,

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is disti ...

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 The grey partridge (''Perdix perdix''), also known as the gray-legged partridge, English partridge, Hungarian partridge, or hun, is a gamebird in the pheasant family Phasianidae of the order Galliformes, gallinaceous birds. The scientific name ...

which have been introduced to the US. Intensive

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

browsing of ''B. tectorum'' in early spring has been used as a fire fuels reduction strategy in the hills adjacent to

Carson City Carson City is an independent city and the capital of the U.S. state of Nevada. As of the 2020 census, the population was 58,639, making it the sixth largest city in Nevada. The majority of the city's population lives in Eagle Valley, on the ...

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

. Because of

rangeland Rangelands are grasslands, shrublands, woodlands, wetlands, and deserts that are grazed by domestic livestock or wild animals. Types of rangelands include tallgrass and shortgrass prairies, desert grasslands and shrublands, woodlands, sava ...

fires and the invasion of ''Bromus tectorum'', in 2010 the United States Fish and Wildlife Service (USFWS) 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 Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

and control has been completed. ''Bromus tectorum'' has demonstrated a quantitative and qualitative response to recent and near-term changes in the concentration of

atmospheric carbon dioxide Carbon dioxide in Earth's atmosphere is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in Earth's atmosphere that are contributin ...

. Laboratory experiments have shown that above-ground biomass increased 1.5–2.7 gram per plant for every 10 part per million (ppm) increase above the 270 ppm pre-industrial baseline. On the qualitative side, rising

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

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 A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

frequency and intensity. ''Bromus tectorum'' has been shown to benefit from endophytic colonization by morels (''

Morchella sextelata ''Morchella sextelata'' is a species of ascomycete fungus in the family Morchellaceae. Described as new to science in 2012, it is found in North America (in Washington, Idaho, Montana, Wyoming, New Mexico, and Yukon Territory). It has also been ...

'', '' M. snyderi'') in western North America.

Treatment options

Seeding

The availability of native seed will always be a limiting factor in restoration of sagebrush ecosystems after a rangeland fire. Little is understood about the germination requirements of native species. This lack of understanding is complicated by the episodic nature of establishment in arid grasslands. In response to the limited availability of native seed, land managers have been seeding ''

Agropyron cristatum ''Agropyron cristatum'', the crested wheat grass, crested wheatgrass, fairway crested wheat grass, is a species in the family Poaceae. This plant is often used as Fodder, forage and erosion control. It is well known as a widespread introduced sp ...

,'' a perennial bunchgrass native to Russia and Asia. The use of seeding another non-native to control an exotic, problem species is called assisted succession. ''A. cristatum'' is much easier to establish than the native perennials and has been shown to be a strong competitor of ''Bromus tectorum.'' However, ''A. cristatum'' can exhibit invasive behavior and is a strong competitor of native perennials. The reason it is used, regardless of its invasive behavior, is because it restores some function a perennial grassland. ''A. cristatum'' is resistant to wildfire and it is suitable forage for cattle and wildlife. But the intensive control that would be needed to establish a native plant community in a ''A. cristatum'' monoculture would cause disturbance that would also increase the invasive species it was planted to out compete. An alternative to using ''A. cristatum'' as a placeholder species in assisted succession is to establish it alongside foundation species like

sagebrush Sagebrush is the common name of several woody and herbaceous species of plants in the genus '' Artemisia''. The best known sagebrush is the shrub '' Artemisia tridentata''. Sagebrushes are native to the North American west. Following is an al ...

. Adding sagebrush would diversity the ecosystem and provide habitat for sagebrush obligates. However, this would mean accepting the possibility that the native plant community may never establish.

Herbicides

A majority of research in 2011-2017 has focused on the use of herbicides to control ''B. tectorum'' and their effect on native plant communities. When using herbicides to suppress winter annual grasses the two most important factors that influence success are application timing and residual soil activity. Application timing is split into three main categories: pre-emergence in the fall before ''Bromus tectorum'' germinates, early post-emergence in early spring when ''B. tectorum'' is a seedling, and late post-emergence in late spring after ''B. tectorum'' is mature. To be most effective post-emergence application needs to be done as late in the spring as possible to ensure that the herbicide treatment hits the majority of the ''B. tectorum'' population. However, the late application puts the native perennial vegetation at risk as they may be coming out of dormancy. Herbicides with no residual soil activity are not generally used because they are only effective in the year of application. If the herbicide has no residual soil activity the herbicide must be applied post-emergence in the early spring, but pre-emergence application is preferred because pre-emergence application is less likely to harm the native vegetation. Studies have suggested that herbicide usage may select for warm season grasses and decrease the abundance of cool season grasses. There are five main herbicides used to control ''B. tectorum'':

imazapic Imazapic is a chemical used as an herbicide. It controls many broad leaf weeds and controls or suppresses some grasses in pasture, rangeland and certain types of turf. It has a half-life Half-life (symbol ) is the time required for a quant ...

, rimsulfuron,

tebuthiuron Tebuthiuron is a nonselective broad spectrum herbicide of the urea class. It is used in a number of herbicides manufactured by Dow AgroSciences, and is sold under several trade names, depending on the formulation. It is used to control weeds, w ...

glyphosate Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...

, and indaziflam. However, the bulk of the recent research has been done on glyphosate, indaziflam, and imazapic. Glyphosate has no residual soil activity and must be used post-emergence, which limits its control of ''B. tectorum'' to one year. For effective control it must be applied to the same area for more than five years to get ahead of seed production to prevent recolonization. Imazapic is the herbicide most widely used by land managers for ''B. tectorum'' control. Of the herbicides listed it is also the most commonly studied. Imazapic is preferred because it can be applied both pre and post-emergence, is approved for rangeland use, and has residual soil activity that allows for one to two year control. Indaziflam is one of the newest herbicides, licensed in 2010. It has a residual soil activity of 2–3 years and its also useful against many other invasive grasses. Not only does it reduce the abundance and biomass of ''B. tectorum'', but it also reduces the highly flammable litter that ''B. tectorum'' produces. In early trials it has consistently out competed imazapic. As of 2017, indaziflam has not been approved for use outside of residential and commercial properties.

Prescribed burning

Prescribed burning A controlled or prescribed burn, also known as hazard reduction burning, backfire, swailing, or a burn-off, is a fire set intentionally for purposes of forest management, farming, prairie restoration or greenhouse gas abatement. A control ...

alone reduces ''Bromus tectorum'' biomass for approximately two years. The goal of a prescribed burn in a ''B. tectorum'' invaded area is to remove the highly flammable plant litter in a controlled manner. The timing of prescribed burns can affect the variety and amount of returning vegetation. A study shows spring burns may result in a significant reduction of native vegetation, but fall burns have been shown to increase species richness. Fall burns may also promote select grasses and fire resilient plants. Another control for ''B. tectorum'' burns is consideration for the densities and fire adaptations of nearby foliage. In some cases, the existence of adjacent morchella can trigger mutual relationships like increased fiber and, by extension, fuels that nurture the return of cheatgrass. Similarly, when densely packed conifers begin infilling sagebrush communities the understory perennial vegetation is reduced; when these areas are prescribed burned the succession is dominated by ''B. tectorum'' in favor of taller grasses, making burns situationally inferior.

Water availability & treatment success

Water availably has a large impact on the success of ''Bromus tectorum'' treatments. In years of high precipitation, ''B. tectorum'' recruitment and biomass will increase and may render the treatment ineffective. In most long-term ''B. tectorum'' studies precipitation differences between years are speculated to be the cause of variation in effectiveness. However, well-timed precipitation after herbicide application can increase the amount of herbicide that makes it into the soil. When herbicide is applied to an area and there is ''B. tectorum'' litter on the ground, much of the herbicide will be absorbed into the litter and some will adhere to the litter. The litter creates a blanket that ''B. tectorum'' can germinate under even after herbicide application. But if it rains shortly after herbicide application, some of the herbicide that is trapped in the litter can be released and work into the soil. The rain may also allow native species to over come herbicide impacts. Increased precipitation in early spring may increase the success of seeding by increasing the germination rate of native grasses and remove ''B. tectorum''’s competitive advantage.

Characteristics of a resistant native community

There is a positive correlation between native vegetation communities and biological soil crust (BSC). 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 Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

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 A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...

grasses have roots that often reach four feet into the soil. These roots provide organic matter, which feeds the

soil organisms Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life, soil biota, soil fauna, or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil ...

, who assist in water and nutrient cycling in arid ecosystems and improve

soil quality Soil quality refers to the condition of soil based on its capacity to perform ecosystem services that meet the needs of human and non-human life.Tóth, G., Stolbovoy, V. and Montanarella, 2007. Soil Quality and Sustainability Evaluation - An integr ...

''. 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. (2014) 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.

References

External links

npwrc.usgs.gov: USGS profile

plants.usda.gov: USDA Plants Profile — ''Bromus tectorum'' (Downy Brome)

Species Profile- Downy Brome (''Bromus tectorum'')
National Invasive Species Information Center,

United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Located ...

— ''lists general information and resources for Downy Brome.''
''Out West, ‘Black Fingers of Death’ Offer Hope Against an Invader''
July 30, 2012

The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid d ...

* https://www.forestsandrangelands.gov/rangeland/documents/SecretarialOrder3336.pdf * https://www.sagegrouseinitiative.com/roots/
Fire Effects Information System
United States Forest Service
Cheatgrass and Wildfire
Colorado State University
CABI Invasive Species Compendium
* {{Authority control tectorum Bunchgrasses of Africa Bunchgrasses of Asia Bunchgrasses of Europe Flora of Lebanon Plants described in 1753 Taxa named by Carl Linnaeus