Schismus arabicus
(Arabian schismus)

S. arabicus is an annual grass from the Old World that has become widespread and invasive in arid and semi-arid regions of North America and Australia. In North America it has become prevalent in parts of the Sonoran Desert and most of the Mojave Desert. In Australia it is confined to southern and western parts. The grass competes for limiting nutrients and water with native annual plants by occupying spaces between desert shrubs. Its numerous fibrous roots form a dense mat beneath the soil surface. S. arabicus promotes fires, because its dead stems readily carry flames and thus increase fire frequencies and the size of burned areas. In southern California, the decline of the native annual grass Vulpia octoflora (six-weeks fescue) is linked to the increase in S.arabicus. Spread is aided by harvester ants carrying seeds to their nests, as seedlings grow better in ant nests than outside.

S. arabicus is native to the Africa, Asia and parts of Europe. It has become widespread and invasive in arid and semi-arid regions of North America and Australia. In North America, it has become prevalent in parts of the Sonoran Desert and most of the Mojave Desert. In Australia, it is confined to southern and western parts.

The grass is unlikely to be introduced intentionally to new areas, but it is likely that it will continue to spread within areas where it has become established.

The grass is listed in the Global Invasive Species Database of the Invasive Species Specialist Group (ISSG, 2012), but it is not listed on any state noxious weed list within the USA.

S. arabicus grows in open and disturbed sites in arid and semi-arid regions. Typical habitats include semi-arid shrublands, roadsides, waste areas, fields, dry river beds and the spaces between desert shrubs (Hickman, 1993; Brooks and Berry, 2006). After disturbance and if bare soil is present, the grass can also colonize coastal shrubland (Brooks, 2000). Within its native range, the grass is an important component of steppes and desert vegetation in Israel, especially in the Negev Desert (Feinbrun-Dothan, 1986). In California, S. arabicus is found from 0 to 1300 m elevation (Brooks, 2000). In Arizona, S. arabicus or S. barbatus occupy an elevation of 395-1580 m (Esque and Schwalbe, 2002).

Genetics

The chromosome number was determined to be 2n=12 for plants from Israel and Libya (Faruqi and Quraish, 1979; Díaz Lifante et al., 1992).

Reproductive Biology

The grass is annual and reproduces by seed. S. arabicus is self-pollinating and self-fertilizing, but it hybridizes with the closely related S. barbatus (Faruqi and Quraish, 1979). Hybrids are fully fertile.

Physiology and Phenology

Flowering time is from January to May in Arizona (Guertin, 2003). The grass will flower until water stress causes senescence (Brooks, 2000). Schismus species are winter annuals and with sufficient rain, germination can occur within two weeks (Pake and Venable, 1995). In North American deserts, S. arabicus is among the first of the winter annuals to flower and the last to die (Pake and Venable, 1995). As a desert annual and winter ephemeral depending on rainfall for germination and growth, it shows great variability in abundance from year to year.

In the southwestern USA, seed germinates in early winter (Brooks, 2000).

In its native range, germination depends on temperature, light conditions and rainfall (Gutterman, 1996a; Gutterman et al., 2010). It can germinate after early winter rains or following later winter rains. The phase of vegetative growth is longer if germination occurs early (Gutterman, 1989). Growth is controlled by day length. The grass has also been observed to germinate following summer rains in southern Egypt and Saudi Arabia (Gutterman, 1996b).

A prolonged after-ripening period is evident in S. arabicus, as the germination rate of stored seeds was higher than that of fresh seeds in plants from its native range (Gutterman, 1996a). Germination in the dark was much higher than in light in a study with seeds from the Negev Desert (Gutterman, 1996a).

Following senescence, plants may remain rooted and standing upright for up to two years. Eventually culms are detaching at the roots and are then blown across the ground (Brooks, 2000).

Population Size and Structure

Abundance of this desert annual varies greatly from year to year because growth and germination depend on rainfall. Once established it may become frequent and cover can reach 45-70% (Howard, 2006). Seed set can be high, e.g. 89 plants covering 1 square metre produced ca 10.000 caryopses (Loria and Noy-Meir, 1979/1980); this gives an average of 112 seeds per plant.

Associations

In the Central Asian Gurbantunggut Desert, the grass is colonized by arbuscular mycorrhizal fungi (Zhang et al., 2012).

Environmental Requirements

S. arabicus is adapted to arid conditions. It emerges during winter and completes its life cycle in spring. In the Negev Desert of Israel, the grass completes its life cycle even in years with less than 100 mm rainfall (Gutterman et al., 2010). In the Central Asian Gurbantunggut Desert, where the grass is a native component of spring ephemerals, mean monthly temperatures range from -20° C to -15° C in January and from 22° C to 26° C in July (Zhang et al., 2012).

The smut fungus Sporisorium aegyptiacum (A.A. Fisch. Waldh.) Vánky occurs on S. arabicus in Australia (Shivas, 2010), but the fungus does not appear to cause significant damage to the plant. In the Central Asian Gurbantunggut Desert, the grass is colonized by arbuscular mycorrhizal fungi (Zhang et al., 2012).

Animal feed, fodder, forage

• Forage

The closely related S. barbatus is distinguished from S. arabicus by lemmas with shorter terminal points constituting15-25% of the total length of the lemma. In S. arabicus, this value amounts to 30-50%. The presence of hairs on the lemma and the length of the palea in S. arabicus are probably the most distinct differences. Nevertheless, both species are annuals and are so similar that distinguishing them is not easy.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control and Sanitary Measures

Grazing is not an ideal method to contain S.arabicus, as stated by Brooks (2000). He notes that although grazing can reduce S. arabicus, Schismus biomass increases following moderate to intense grazing, because grazing animals cause soil disturbances and reduce shrub cover. This promotes further spread of the grass.

Physical/Mechanical Control

Hand removal is impractical due to the plant’s small size (Brooks, 2000). Due to the extensive mat of roots under the soil surface, pulling up the grass causes substantial soil disturbances, thereby creating conditions which encourage further establishment of S. arabicus (Brooks, 2000). The same holds for ploughing, disking or scraping. Fire generally promotes the growth of S. arabicus.

Chemical Control

A late application of glyphosate or grass-specific herbicides has proven to be effective in killing plants (Marushia et al., 2010). If fuel accumulation and seed set are to be prevented, herbicides need to be applied at the pre-bolting rosette stage. However, the small surface area of the leaves and culms makes herbicide application difficult (Brooks, 2000).

Studies on the long-term ecological effects of this grass are largely lacking. The role of fires in spreading this invasive grass is not yet fully understood and here studies are badly needed. Many studies do not distinguish between S. arabicus and S. barbatus, hence exact data on local distribution and abundance of S. arabicus are often lacking.

USA: California Invasive Plant Council (Cal-IPC), 1442-A Walnut Street, #462, Berkeley, California, CA 94709, http://www.cal-ipc.org/

02/01/13 Original text by:

Ewald Weber, Consultant, Germany