Invasive Plants of California's Wildland

Schismus barbatus and S. arabicus are so genetically and morphologically similar (Faruqui and Quarish 1979, Faruqui 1981, Bor 1968), with similar geographic ranges and habitats in California (Hickman 1993), that they are treated together here.

Mediterranean grass (Schismus barbatus or S. arabicus) is a small, tufted annual grass with erect or spreading, green, smooth culms to eight inches, often with brown nodes. Individual plants can remain rooted and upright for up to two years following death, but eventually detach at ground level and blow across the ground like a tumbleweed, falling apart in the process. Mediterranean grass is most common in the spaces between shrubs, often producing a carpet of green that turns purplish at maturity and fades to a light straw color soon after death.

Mediterranean grass is found below 4,250 feet (1300 m) elevation in disturbed and undisturbed areas of the central and southern coastal regions, the Central Valley, and the deserts of California. Schismus arabicus is generally more common in arid regions, whereas S. barbatus is more common in semi-arid shrublands, extending into the northern coast to Mendocino County. Mediterranean grass is most common in spaces between shrubs where it is not shaded by taller plants. It is widespread and common in the desert (Brooks 1998); its presence in coastal shrubland may not be readily apparent except on bare soil or following fire, where it can appear in great numbers.

Mediterranean grass is native to southern Europe, northern Africa, and the Near East (Jackson 1985) and has spread to areas of North America, South America, Australia, and the west coast of Europe where Mediterranean climate regimes occur (Bor 1968). It appears to have spread westward from Arizona into California during the early 1900s (Burgess et al. 1991), and was first recorded in California in 1935 (Robbins 1940). Mediterranean grass is particularly abundant where grazing, off-road-vehicle use, or construction of linear corridors has reduced shrub cover and disturbed the soil. Seeds disperse by sheet flooding and by wind and often persist within the inflorescence, detaching after it is blown across the ground for a short distance from the parent plant.

Mediterranean grass rose from relative obscurity to become one of the dominant annual grasses in arid and semi-arid regions of California during the 1940s (Clarke, pers. comm.). As Mediterranean grass became more dominant, the similar native annual grass, six-weeks fescue (Vulpia octoflora) became less common (Clarke, pers. comm.). Mediterranean grass can compete effectively for limiting nutrients with native annual plants that occupy spaces between shrubs (Brooks 1998).

Fire is readily carried across inter-shrub spaces by the dead stems of Mediterranean grass (Brooks 1998, Brooks in press), which may have contributed to the increasing frequency and extent of fire in recent decades in California deserts.

Mediterranean grass reproduces by seed only. Seeds are tiny and dust-like (Loria and Noy-Meir 1979, 1980), and disperse into small cracks and depressions in the soil (Gutterman 1994). Only a fraction of the seedbank germinates during a given year, leaving most seeds in reserve for future years when the cohort may die prior to reproduction (Gutterman 1994). This bet-hedging strategy is characteristic of annual plants that have evolved in arid desert regions with locally variable rainfall patterns, and it predisposes Mediterranean grass to successful establishment in California deserts.

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Mediterranean grass is a winter annual, germinating in early winter following 0.4 inches (10 mm) or more of rainfall and emerging about two weeks later. It grows little until early spring (typically March), when rainfall and higher temperatures stimulate accelerated growth and flowering. Progression from seedling to flowering stages can

Mediterranean grass is generally intolerant of shading, which may explain its association with inter-shrub spaces. However, it can thrive under perennial shrubs, particularly under south canopies or where tall-statured annual plants are less common (Brooks 1998). The root system can form an extensive mat near the surface where plant litter is present.

Mechanical methods: Its small size makes hand thinning of Mediterranean grass impractical. In addition, the extensive mat of roots near the surface of the soil often results in significant disruption of the soil surface when plants are removed, which may promote further weed establishment. Plowing, disking, or scraping may initially reduce surface biomass of Mediterranean grass, but soil disturbance and reduced shading results in improved site conditions for this species.

Prescribed burning: Fire generally promotes the growth of Mediterranean grass. Its small seeds settle near or beneath ground level, where they are protected from high temperatures. Significant seed death occurs only under perennial shrubs where intense burning heats deeper into the soil. After fire has removed plant litter and taller competitors, and in some cases has increased soil nutrients, Mediterranean grass can dominate until plant litter and populations of taller annual plants become reestablished. Prescribed burning generally is counterproductive to the control of Mediterranean grass. However, if the choice is between controlling Mediterranean grass or more problematic annual weeds that may be controlled by certain fire prescriptions, then the latter should usually receive priority.

Insects and fungi: No USDA approved insects or fungi to be used as biocontrol agents exist for these grasses. Ants feed on the seeds of Mediterranean grass in its native range (Gutterman 1993) and in North America (Rissing 1988). Ants generally harvest seeds while they are still concentrated within the inflorescence. After dispersal the seeds spread out across the landscape and settle into small cracks in the soil, thereby hindering predation (Gutterman 1994).

A black smut, Ustilago aegyptica , can form on Mediterranean grass, destroying the spikelets (Gilbertson and Blackwell 1988). Natural infestations of smuts do not seem to be widespread or severe enough to significantly affect populations of Mediterranean grass in California. However, inoculation of smuts into areas of the desert could prove to be useful for short-term control of Mediterranean grass and other alien annual grasses, as long as they do not affect native perennial grasses. Especially in years of abundant rainfall, smuts may reduce the density of alien annual grasses prior to revegetation efforts. This would have to be researched and approved by the USDA and the CDFA Biological Control Program before such distribution would be permitted.

Grazing: Livestock grazing can remove biomass of Mediterranean grass. However, the relative biomass of alien annual grasses compared to native annuals tends to increase following moderate to intense grazing. Mediterranean grass is particularly dominant in ephemeral sheep grazing allotments in the California desert. As with mechanical plowing, reduced shrub cover and increased soil disturbance caused by grazing ultimately improve site conditions for Mediterranean grass.

Various herbicides, including glyphosate, can control Mediterranean grass, but the small surface area of the leaves and culms make application problematic. In addition, broadcast herbicides would negatively affect non-target species.