Drooping Brome

Bromus tectorum Drooping brome (Eu), Cheat Grass (N.Am)
Left: Drooping Brome Bromus tectorum Right: Field Brome Bromus arvensis
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Monocots
(unranked):	Commelinids
Order:	Poales
Family:	Poaceae
Genus:	Bromus
Species:	B. tectorum
Binomial name
Bromus tectorum L.

Drooping brome or Cheat Grass, Bromus tectorum, is a grass native to Europe, southwestern Asia and northern Africa.

Description

Bromus tectorum is an annual bunchgrass, usually germinating in the autumn, overwintering as a seedling, then flowering in the spring or early summer. If winter rainfall is limiting and spring moisture is adequate, the seeds will germinate in the spring, and the plants will flower that summer. It typically reaches 40–90 cm tall, though plants as small as 2.5 cm may produce seed. It is cleistogamous and self-fertile, with no evident out-crossing.

Below grade

Drooping Brome or Cheat Grass has an extensive root system. The wide-spreading lateral roots are one of the keys to the survival of this plant. A study showed that it had the capability to reduce soil moisture to the permanent wilting point to a depth of 70 cm, reducing competition from other species.

Seeds

The seeds 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. It 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, it may produce 450 kg of seed per hectare with about 330,000 seeds/kg.

The seeds maintain high viability in dry storage, lasting over 11 years. In the field, under buried conditions, seeds will lose their viability in 2–5 years. The primary limit to germination is inadequate moisture. Seeds can withstand high soil temperatures. 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 of soil, and a few plants emerge from depths of 8 cm, but not from seeds 10 cm below the surface.

Habitat

Drooping Brome or Cheat Grass (Bromus tectorum) grows in many climatic areas. It is found primarily in the 150–560 mm precipitation zone. It will grow in almost any type of soil, including B and C horizons of eroded areas and areas low in nitrogen. 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.

Status as an exotic weed

Drooping Brome, northern Nevada

Drooping Brome 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 (where it is known as Downy brome or Cheatgrass) in 1861 in New York and Pennsylvania, by 1928 reaching throughout the United States (including Hawaii and Alaska), except for Florida and portions of Alabama, Georgia, South Carolina; it 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.

Invasive species

Cheat Grass (Bromus tectorum) is an invasive species in California.^[1][2]

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. Drooping Brome 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 Cheatgrass in early spring has been used as a fire fuels reduction strategy in the hills adjacent to Carson City, Nevada.

Drooping broom 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 (ppm) increase above the 270 ppm pre-industrial baseline. On the qualitative side, rising carbon dioxide decreased the digestibility and potential decomposition of drooping brome. In addition to stimulation of biomass, rising carbon dioxide may also increase the above ground retention of drooping broom biomass by decreasing removal by animals or bacteria. Ongoing increases in atmospheric carbon dioxide may contribute significantly to drooping broom productivity and fuel load with subsequent effects on wildfire frequency and intensity.^[3][4]

See also

• Invasive grasses of North America

References

1. ^ http://www.cal-ipc.org/ip/inventory/index.php accessed: 6/6/2010
2. ^ http://www.nps.gov/yose/naturescience/invasive-plant-management.htm accessed: 6/6/2010
3. ^ Ziska, L.H.; Reeves III, J.B.; Blank, R.R. (2005), "The impact of recent increases in atmospheric CO₂ on biomass production and vegetative retention of cheatgrass (B. tectorum): Implications for fire disturbance.", Global Change Biology. 11 (8): 1325–1332, doi:10.1111/j.1365-2486.2005.00992.x 
4. ^ Global Fire Initiative: Fire and Invasives, The Nature Conservancy, http://www.tncfire.org/crosscutting_fandi.htm, retrieved 2008-12-12 

External links

• npwrc.usgs.gov: USGS profile
• plants.usda.gov: For information on this plant
• Species Profile- Downy Brome (Bromus tectorum), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Downy Brome.