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May 2009. A question about the potential environmental impact of Brachiaria decumbens in the Federated States of Micronesia, elicted much comment from members. There was also a similar question about Japanese millet, Echinochloa utilis.
Signal grass was hydroseeded for erosion mitigation along the Compact Road in Palau during the years of construction, 2001 to 2007 or thereabouts. So far, there are no reports of it moving out of the seeded areas. However, there is evidence elsewhere, in savanna sites, where this grass is used for mulch, that it has potential to invade savanna and/or grassland areas. It is reportedly not shade tolerant, so is unlikely to invade forest.
Japanese millet, Echinochloa utilis, was also hydroseeded, germinated very rapidly and eventually died out.
A member from Brazil mentioned the usefulness of Brachiaria brizantha in coffee plantations (in the “Cerrado”), where it is used as a mulch to lower soil temperature, reduce evaporation and weed control – B. ruziziensis and B. decumbens are used for the same purpose (see photo). It is also used to protect the soil from high rainfall. The dry matter production is high with a good C/N ratio.
The grass is a very useful pasture species in some countries like Vanuatu and PNG. It only becomes prominent in disturbed areas and does not necessarily invades intact forest areas. It is a poor competitor under shady conditions.
References
Brachiaria decumbens Stapf is the synonym of Urochloa brizantha (C. Hochstetter ex A. Rich.) R. Webster (Integrated Taxonomic Information System) also refrred to as Urochloa decumbens (Stapf) R.D. Webster in literature.
It is described as an agricultural weed, cultivation escape, environmental weed, naturalised, weed in the Global Compendium of Weeds http://www.hear.org/gcw/species/brachiaria_decumbens/
In the PIER database it is listed as Urochloa decumbens (Stapf) R.D. Webster, and there is a link to a risk assessment as well as distribution information for the Pacific region:
http://www.hear.org/Pier/species/urochloa_decumbens.htm
A pest in Australia. Signal grass is recorded as having severe impact on native grasses in the Brazilian savanas.
Pivello et. al. (1999a) Alien grasses in Brazilian savannas: a threat to the biodiversity. Biodiversity and Conservation 8: 1281-1294.
Pivello et. al. (1999b) Abundance and Distribution of Native and Alien Grasses in a “Cerrado” (Brazilian Savanna). Biological Reserve Biotropica Vol. 31(1): 71-82.
Barbosa et. al. (2008) Allelopathic evidence in Brachiaria decumbens and its potential to invade the Brazilian Cerrados. Braz. arch. biol. technol. Vol. 51(4).
Williams & Brauch (2000) African Grass Invasion in the Americas: Ecosystem Consequences and the Role of Ecophysiology. Biological Invasions Vol. 2(2): 123-140.
Echinochloa utilis is the synonym of Echinochloa esculenta (A. Braun) H. Scholz (Integrated Taxonomic Information System).
Listed as Echinochloa esculenta (A. Braun) H. Scholz in PIER, risk assessment score is ‘high’
http://www.hear.org/pier/species/echinochloa_esculenta.htm
The annotations which form part of the risk assessment may be useful to you
http://www.hear.org/Pier/wra/pacific/echinochloa_esculenta_htmlwra.htm
Listed as Echinochloa esculenta in Global Compendium of Weeds described as an ‘agricultural weed, casual alien, environmental weed, naturalised, weed’
http://www.hear.org/gcw/species/echinochloa_esculenta/
See also HEAR references:
http://www.hear.org/Pier/species/urochloa_decumbens.htm
http://www.hear.org/gcw/species/brachiaria_decumbens/
http://tinyurl.com/urochloadecumbensweed
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