Ione Manzanita

Arctostaphylos myrtifolia

Description

Ione manzanita, Arctostaphylos myrtifolia, is an evergreen shrub of the heath family (Ericaceae) that lacks a basal burl. Attaining a height of generally less than 3.9 ft (1.2 cm), plants appear low and spreading. The bark is red, smooth, and waxy. Olive green, narrowly elliptic leaves are 0.2-0.6 in (5.1-15.2 mm) long. Red scalelike inflorescence (flower cluster) bracts are 0.04-0.08 in (1.0-2.0 mm) long. White or pinkish urn-shaped flowers appear from January to February. The fruit is cylindric. The species depends almost entirely on periodic fire events to promote seed germination. Ione manzanita can be distinguished from other species in the same genus by its smaller stature and the color of its leaves.

Scientists have observed mature individuals in well-established, undisturbed natural stands die. The species appears to have a low regenerative potential in closed stands. Individual plants are thought to live not much longer than 50 years. Individuals maintained in cultivation for many years have died suddenly for no apparent reason.

The effects on A. myrtifolia of changing the frequency of occurrence of fire have not been well-studied. A. myrtifolia lacks the ability to crown sprout and is killed outright by fire. It must, therefore, reproduce by seed, and has produced abundant postfire seed germination.

Fire, therefore, appears to be necessary for the long-term maintenance of the Ione chaparral community. Controlled burning may be a viable means of ensuring adequate reproduction of A. myrtifolia, or perhaps even controlling or preventing loss due to the fungal pathogen. Field observations and controlled experiments to date, however, suggest exercising caution in the use of fire until the reasons for the variability in the response of A. myrtifolia are better understood. Progress toward better understanding of the response of A. myrtifolia to fire was thwarted when long term study sites established to study this response were graded and cleared by the landowner.

Habitat

Ione manzanita is found primarily at elevations between 295 and 918 ft (90 and 280 m) in Ione soils.

Distribution

Ione manzanita is reported from 17 occurrences. Because most of these occurrences are based on the collection localities of individual specimens, it is uncertain how many stands these 17 occurrences represent. Ione manzanita may occur in about 100 individual stands, which cover a total of about 1,000 acres (400 hectares). It occurs primarily on outcrops of the Ione formation within an area of about 35 sq mi (90.1 sq km) in Amador County, California. In addition, a few disjunct populations occur in Calaveras County. The populations range in elevation from 190 to 1,900 ft (57.9 to 579 m), with the largest populations occurring at elevations between 280 and 900 ft (85.3 and 274.3 m). Ione manzanita is the dominant and characteristic species of Ione chaparral, where it occurs in pure stands. It also occurs in an ecotone with surrounding taller chaparral types, but it does not persist if it is shaded.

Threats

An unidentified fungal pathogen has caused major dieback of partial or entire stands of Ione manzanita throughout its range. The majority of populations of Ione manzanita show signs of dieback. The fungal disease is a serious problem for the populations south of Ione. Stands along Highway 88 that were healthy a few years ago are apparently being killed with little evidence of seedling regeneration. The fungal problems are clearly due to senescence (extreme aging) of older individuals and pathogen loads that build up with crowding and accumulation of organic debris due to fire suppression.

Although state law exempts the taking of listed plants, the law does not necessarily prohibit activities that could extirpate this species. After California Department of Fish and Game notifies a landowner that a state-listed plant grows on his or her property, state law requires only that the landowner notify the agency at least 10 days in advance of changing the land use to allow salvage of such a plant. Ten days may not allow adequate time for agencies to coordinate the salvage of the plants.

A. myrtifolia, is threatened by vandalism. A 106-acre (42.9-hectare) parcel of land previously identified in a public document as occupied habitat for this species was cleared in 1993, presumably to facilitate future development. In July 1997, shortly after the proposed listing rule was published in the Federal Register, unknown vandals destroyed a scientific propagation study plot for A. myrtifolia on lands managed by the U.S. Bureau of Land Management (BLM).

Throughout its range, on habitat edges where better soil development occurs, A. myrtifolia is being outcompeted by other native vegetation. A. viscida (white leaf manzanita), a more rapidly growing, taller manzanita, encroaches along the edge of stands of A. myrtifolia. A. myrtifolia is eliminated when A. viscida grows tall enough to shade it. This is not likely to be a significant threat to the species, however, because most stands occur on substrates from which taller shrubs are excluded.

Conservation and Recovery

All three occurrences of Ione manzanita on federal lands are managed by BLM. One of these occurrences lies within the Ione manzanita area of critical environmental concern. On federal lands, modification of occupied habitat by any action authorized by BLM is unlikely to occur without consultation because BLM managers are well aware of the presence and locations of Ione manzanita. Establishment of an area of critical environmental concern indicates that the BLM will give the protection of the rare plant community on this parcel the highest priority in all management decisions. BLM also prohibits grazing in the area of critical environmental concern, and has implemented erosion control measures on an off-road vehicle course previously used by California Department of Forestry and Fire Protection. In addition, the BLM has functionally withdrawn the area of critical environmental concern and other habitats known to be occupied by the species from mineral entry and has developed a management plan for the area of critical environmental concern. BLM has also authorized experimental transplantation studies on the area of critical environmental concern.

Botanists have attempted a variety of germination and seed bank experiments on A. myrtifolia without success. Although the plant has a limited capacity to root from its lower branches, not even a single plant has been grown or cultivated from a rooted branch. The only report of successful cultivation indicates that the plant requires high soil acidity and heavy supplements of soluble aluminum.

Contact

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

Reference

U. S. Fish and Wildlife Service. 26 May 1999. "Determination of Endangered Status for the Plant Eriogonum apricum (inclusive of vars. apricum and prostratum ) (Ione Buckwheat) and Threatened Status for the Plant Arctostaphylos myrtifolia (Ione Manzanita)." Federal Register 64 (101): 28403-28413.