Drooping Brome
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 Left: Drooping Brome Bromus tectorum
Right: Field Brome Bromus arvensis |
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| Bromus tectorum L. |
Drooping brome (Bromus tectorum), is a grass native to Europe, southwestern Asia and northern Africa.
It is an annual, 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. 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.
Drooping Brome 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.
The seeds maintain high viability in dry storage, lasting over 11 years. In the field, under buried conditions, seeds will loose their viability in 2-5 years. The primary limit to germination is inadequate moisture. Seeds can withstand very 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.
[edit] Habitat
Drooping Brome 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.
[edit] Status as an exotic weed
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 and Columbia Basin.
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, as it out-competes native perennial grasses by being more tolerant of grazing and trampling by livestock while providing much less nutrition. In addition, it re-establishes itself quickly after fires, and being an annual has the effect of accelerating the fire cycle to the detriment of native shrubs such as sagebrush. On the other hand, Drooping Brome seeds are a critical portion of the diet of the Chukar and Grey Partridge which have been introduced to the US.
