Invaders
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Buffelgrass (Pennisetum ciliare)

Buffelgrass is a shrubby grass to 1.5 feet tall and 3 feet wide. It looks like a bunchgrass when small (either a seedling or recently burned, grazed, or cut). Older plants branch profusely and densely at nodes, giving mature plants a messy appearance. These nodal branches produce new leaves and flower spikes very quickly after light rains, making buffelgrass an extremely prolific seed producer.

Some native grasses such as Arizona cottontop (Digitaria californica) branch sparsely and do not appear shrubby. Bush muhly (Muhlenbergia porteri) is a true densely-branched shrub; it differs from buffelgrass in its very delicate texture.


An entire mature plant.


A single basal stem teased out, showing the profuse branching above ground.

Inflorescences are 1.5 to 5 inches long, fat brown to purplish when fresh or occasionally straw-colored. The spikes are crowded with dense bristly fruit which are actually burs without hardened spines. (For this reason buffelgrass is sometimes included in the genus Cenchrus, the burgrasses.) This is primarily a warm-season grass, but below 3000 feet in our region it can grow and flower after almost any rain.


The individual units visible in these buffelgrass inflorescences are basically soft burs.

The most similar native grass is plains bristlegrass (Setaria macrostachya). The individual seeds are clearly visible.

Why is it a Threat?

Buffelgrass grows densely and crowds out native plants of similar size. Competition for water can weaken and kill larger desert plants. Dense roots and ground shading prevent germination of seeds. It appears that buffelgrass can kill most native plants by these means alone.

Tumamoc Hill in Tucson, home of the University of Arizona's historic Desert Laboratory visible at left, has been overrun by buffelgrass in the last two decades. It has not burned, but native plants are declining and dying from lack of water. Photos: Travis Bean

[Red brome (Bromus rubens) is another invasive grass that has covered huge areas of lower bajadas in the upper Sonoran Desert. This annual grass has caused serious damage in the past several decades. It grows densely only in wetter years and produces relatively mild fires, so fires are infrequent and don't completely kill native communities in one episode. Nonetheless conversion is progressing where it has invaded.]

Buffelgrass is a very drought-tolerant perennial, so it can remain dense and even spread in dry years. It is present to burn year round and supports hotter fires than those of red brome. The Sonoran Desert evolved without fire as an ecological factor and most of its plants cannot tolerate it. A single buffelgrass fire kills nearly all native plants in its path. The buffelgrass invasion is now destroying steep hillsides compared to red brome's flatter terrain, and is rapidly converting formerly rich biological communities into monocultural wastelands.


A "natural" roadside with native vegetation. AZ Hwy 85 in Organ Pipe Cactus National Monument, where buffelgrass is controlled.

The shoulders of this road near Saric, Sonora are almost 100% buffelgrass, a common result where it isn't controlled. Buffelgrass is abundant in the adjacent hills, but heavy grazing keeps it from reaching burnable density.

Buffelgrass resprouts vigorously after fires, but most native desert plants are killed. Near Caborca, Sonora.

This hillside near Caborca, Sonora recently burned, killing nearly all of the native plants. Only charred skeletons of teddy bear cholla (Cylindropuntia bigelovii) and a palo verde (Parkinsonia microphylla) are visible. The rich Arizona Upland vegetation that once grew here can be seen in the distance.

There is growing evidence that buffelgrass depletes soil fertility in a decade or so. It then dies and leaves behind a sterile wasteland. No one knows how much time will be needed to restore such ruined land.

Distribution

Native to the Old World where it is widespread in Africa, the Middle East, Indonesia and nearby islands, and tropical Asia. Introduced to Australia and the New World.

In the Sonoran Desert Region buffelgrass is common in southern Arizona and most of Sonora.

Habitat

There are two seemingly unrelated habitats in the Sonoran Desert. In valleys and lower slopes buffelgrass invades disturbed areas such as roadsides and cleared or grazed fields. It Arizona it is spreading very rapidly along medians and shoulders of major highways and more slowly on smaller roads. In northern Sonora it has been present longer, and it dominates long stretches of smaller highways. From the town of Imuris, Sonora buffelgrass extends in a continuous ribbon along highway 15 all the way to Sinaloa, interrupted only by a few cities.


A typical roadside habitat for buffelgrass (under the stopsign). The larger grasses are the related fountaingrass (Pennisetum setaceum), which is also a serious invasive threat.

This cleared field is nearly pure buffelgrass. It has not dominated the surrounding flats which have not been cleared of vegetation.

Its other habitat is steep rocky hillsides, mosly east- and south-facing slopes. It is most abundant on debris cones near the angle of repose. These steepest slopes may be the best establishment sites from which it will eventually spread. Some less steep hillsides are completely covered with buffelgrass, so the invasion may still be in its early stages. It occurs from near sea level to 4150 feet elevation.


A steep rocky hillside in the Pan Quemado Mts, Ironwood Forest National Monument. Several patches of buffelgrass are visible.

Buffelgrass being censused on a hillside near Magdalena, Sonora. Most of the herbaceous plants have disappeared.

History

Buffelgrass was introduced to the United States about in the1930s as livestock forage. It was in planting trials at the Soil Conservation Service nursery in Tucson from 1938 to 1952. Several experimental plantings were done beginning in 1941 at Aguila near Phoenix. Most did not do well. (Another planting in Avra Valley west of Tucson in the early 1980s also died out where it was planted on flat ground.)

Records of collections in natural habitat were sparse until about 1980 when it began a rapid expansion. One example is Organ Pipe Cactus National Monument, where buffelgrass was rare before 1984 (Felger 1990). By 1994 it had occupied 20-25 square miles and was expanding rapidly. Few people other than botanists noticed it in Arizona before 1990. Today it is difficult not to see it in the southern half of the state.

Survey

A survey of roads done by the Desert Museum in 2004 revealed the full extent of the buffelgrass invasion of Arizona and northern Sonora (maps below).
Read the full report:
PDF format
MS Word format.


Buffelgrass distribution along roads in Arizona and northern Sonora. Red symbols in maps denote areas where buffelgrass is the dominant plant and dense enough to burn.

Buffelgrass distribution along roads in the Tucson vicinity. The survey was not completed within the urbanized zone; buffelgrass is present here in nearly every vacant lot and unpaved road shoulder.

Buffelgrass distribution along roads in northern Sonora.

Buffelgrass distribution along roads in northeastern Sonora.

What can be Done

Buffelgrass can be controlled by manual pulling and herbicides. Organ Pipe Cactus National Monument nearly eradicated patches covering ca. 25 square miles in three years of intensive manual labor. After the initial control only minor efforts have been required to destroy new infestations (though searching the huge park takes a great deal of time). Volunteer groups such as Sonoran Desert Weedwackers are active in controlling it in other areas such as Tucson Mountains Pima County Park.

The highest priority should probably be to control buffelgrass on roads outside of urban zones, because these are the seed sources for invasion of natural habitats. Second priority should go to the most valuable habitats such as parks.

In the long run we may need biological control. This will be a controversial issue because buffelgrass is still valued as livestock forage. To this issue, it must be publicized that buffelgrass is not nearly as economically viable as first thought. Research in Africa, Australia, South America, Texas, and Sonora reveal that the average useful life of a buffelgrass pasture is only 10-12 years. Under exceptional management productive pastures have lasted only 15 or 16 years (Ibarra 1999). Buffelgrass impoverishes the soil and evenually dies, leaving behind a sterile wasteland that requires expensive efforts to restore productivity.

The public and land management agencies must be educated to recognize Buffelgrass for the threat that it is. The state of Arizona declared it to be a noxious weed in March 2005. On the other hand, at least one branch of the federal government is breeding buffelgrass to develop more cold-hardy varieties.

Other common names: African foxtail grass, anjan grass, syn. Cenchrus ciliaris.

Links

Federal Noxious Weeds list

Forestry Images (Many images of invasive plants and animals)

Invaders Database System, Univ. of Montana

U.S. Dept. of Agriculture Noxious Weeds Website

U.S. Govt. Invasive Species Website

References

Tellman, Barbara (ed.). 2002. Invasive Exotic Species in the Sonoran Desert Region. University of Arizona Press.

Ibarra F., Fernando. 1999. Lo mejor del dia del ganadero. Summary of oral presentation on website.