Alopecurus aequalis var. sonomensis
|Listed||October 22, 1997|
|Description||A tufted, perennial grass.|
|Threats||Competition from invasive alien plants, trampling and feeding by cattle, and low reproductive success.|
Sonoma alopecurus, Alopecurus aequalis var. sonomensis, is a tufted perennial in the grass family (Poaceae) that reaches 12-30 in (30-76 cm) in height. The stems are mostly erect and either straight or weakly bent near the base. The leaf blades are up to 0.3 in (7 mm) wide, the panicle is 1-3.5 in (2-9 cm) long and 0.1-0.3 in (2-7 mm) wide, and the spikelets are usually tinged violet-gray near the tip. The bristlelike awn is straight, exceeding the lemma body by 0.04-0.1 in (1-2 mm).
This variety is distinguished from A. aequalis var. aequalis by its more robust and upright appearance, generally wider panicle, violet-gray tinged spikelets, and longer awn.
Peter Rubtzoff described Alopecurus aequalis var. sonomensis in 1961 from a specimen collected six years earlier in Guerneville Marsh, Sonoma County, California. Specimens assignable to this species were collected as early as 1880 in Sonoma and Marin Counties, but they had been identified as A. aequalis sobol, a circumboreal foxtail grass found as far south as adjacent Mendocino County. These specimens, however, deviated considerably from typical A. aequalis and were identified as A. aequalis var. sonomensis. Although William Crins only referred to this variety in passing in a discussion of the species in 1993, its morphological and ecological attributes clearly make it a distinct variety.
All populations of Sonoma alopecurus occur in moist soils in permanent freshwater marshes at elevations between 20 and 680 ft (6-207 m).
Sonoma alopecurus was known from five natural populations when it was first proposed for listing in August 1995. Three sites in Sonoma County were privately owned, while two sites were on federal land within Point Reyes National Seashore in Marin County. Three more natural sites in Marin County have been identified since 1996, two of which are on federal land within Point Reyes National Seashore and one of which is a private inholding within the Point Reyes National Seashore. One of the newly discovered populations was initially thought to be the result of seeds washed down from a reintroduced population, but it is now considered a natural population. A population thought to have been destroyed by a flash flood in 1993 reestablished itself, containing 15 plants in 1994 and 13 in 1995.
Sonoma alopecurus was known historically from 16 populations. The historical range of this plant was approximately 30 mi (48 km), extending north from Point Reyes Peninsula to Guerneville and east to Cunningham. Although fewer than half of the historical sites are now extant, the range of the species has changed little.
Populations of Sonoma alopecurus usually have about 100 or fewer individuals, although the number of individuals per group can fluctuate markedly between years. The largest population recorded in recent years was about 600 plants in 1995; this population dropped to about 100 plants in 1996. A population in Sonoma County reported to have 150 individuals in 1987 had dropped to only four plants by 1994.
Sonoma alopecurus is threatened by competition from invasive plant species, trampling and grazing by cattle, and low reproductive success. Competition with invasive plant species or excessive cattle grazing threatens at least five of the eight remaining populations of this species.
An operating wastewater treatment plant could potentially threaten one population, and destructive random events are always a general threat to local populations.
Rushes (Juncus spp.) and nutsedges (Cyperus spp.) are invasive emergent wetland species so competitive that they have nearly extirpated one population of Sonoma alopecurus.
Grazing and ranching have occurred on the Point Reyes Peninsula for more than a century, and the Point Reyes National Seashore has 17 cattle and dairy ranches within its boundaries, despite being part of the National Park system. A 1986 study stated that grazing had been a serious threat to Sonoma alopecurus occurrences located on this National Seashore, although more recent reports indicate concerns about both too much and too little grazing.
Seven of the eight known sites of Sonoma alopecurus are currently being (or have recently been) grazed by cattle. All three populations in Sonoma County are now threatened by cattle grazing, as is a portion of one population outside of a fenced area on the Point Reyes National Seashore, where three small patches disappeared from a gathering place for cattle during a week-long period of observation. The portion of the population inside of the fenced area decreased from 603 flowering culms (stems) in 1995 to 195 flowering culms in 1996, possibly due to annual fluctuation or competition from other vegetation.
Another Sonoma alopecurus population on the Point Reyes National Seashore was fenced from cattle in 1987; the number of individuals at this site ranged from zero in 1990 and 1993 to 14 in 1991, possibly due to competition from a dense growth of other marsh plants. Experiments have been conducted since then with partial opening and closing of the entry gate, but few cattle found their way in and no plants have been seen at this site since 1991. These results suggest that some grazing may be necessary to maintain Sonoma alopecurus populations in the face of competition from other plants, but that excessive grazing by cattle can damage or eliminate individuals of this species.
Sonoma alopecurus is also not readily propagated. The plant appears to have very strict habitat requirements, and suitable habitats occur in only four locations within the Point Reyes National Seashore. Three attempts at establishing new populations by seeding seemingly suitable habitat on the Point Reyes National Seashore have failed, as has an attempt to start a population in the East Bay Botanic Garden in Tilden Park.
The historical range of Sonoma alopecurus also occurs within the project boundaries of a waste-water treatment plant, currently operating without discharging recycled wastewater onto surrounding sensitive habitat. Should the treatment plant do so, as was originally planned before construction commenced, the hydrology of the habitat drenched with wastewater could be adversely affected, with probably harmful consequences to this species.
Naturally occurring floods also may be an ongoing threat. One population was damaged by a flash flood in 1993.
Conservation and Recovery
The Sonoma alopecurus is only known from eight locations, four of which are on Federal land within the Point Reyes National Seashore. These critical habitats must be protected against threatening activities, particularly invasive alien plants and ungulate herbivores. The other four locations are on private land, and are potentially vulnerable to various kinds of threatening influences. The largest of these private habitats should be protected. This can be done by acquiring the land and establishing ecological reserves, or by negotiating conservation easements with the landowners. The populations of the Sonoma alopecurus should be monitored, and research undertaken into its biology and ecological requirements.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Orgeon 97232-4181
Telephone: (503) 231-6121
U. S. Fish and Wildlife Service
Sacramento Field Office
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619
U. S. Fish and Wildlife Service. 22 October 1997. "Endangered and Threatened Wildlife and Plants: Determination of Endangered Status for Nine Plants From the Grasslands or Mesic Areas of the Central Coast of California." Federal Register 62 (204): 54791-54808.