Morro Manzanita

Arctostaphylos morroensis

Description

Morro manzanita, Arctostaphylos morroensis, is a handsome shrub that reaches a height of 5-13 ft (1.5-3.9 m) and has crowded oblong to ovate grey-green to olive-green leaves, 1-1.5 in (2.5-3.8 cm) long. The white to pinkish flowers are 0.2-0.3 in (0.5-0.76 cm) long, and form orange-brown fruits with eight to 10 stones per fruit that are fused but separable. Morro manzanita is distinguished from other manzanitas in the area by the following characteristics: the bark of the trunk is a shaggy grey to brown; the leaf blades range from wedge-shaped (cuneate) to rounded or nearly straight (truncate) at the base, with the lower surface paler and usually somewhat tomentose (short woolly hairs). Occasional specimens of Morro manzanita have small projecting lobes at bases of the leaf blades and a short leaf stalk or none at all—characters more representative of the rare La Cruz manzanita (A. cruzensis ), which occurs in the same area.

Morro manzanita flowers in winter, with fruit maturing and seed dispersing in summer and fall. Seeding is its only means of reproduction. Unlike some other manzanitas, Morro manzanita lacks a woody burl from which it can resprout following a fire. Typically, when obligate-seeding manzanita individuals are consumed by fire, stand regeneration depends on relatively long-lived seeds that remain viable in a soil seedbank. Dormancy mechanisms inhibit seed germination until the proper environmental conditions, such as a fire, occur that scarify the seeds and provide open sites in which seedlings can establish. Recent studies found that Morro manzanita seeds were typically very common under the canopies of adult individuals, but not beyond the canopy. Under canopies seed densities were estimated at 12,000-37,000 seeds per sq m (1 sq m=10.8 sq ft), although viability of the seeds was less than 5%. About 80% of the seeds were found in the top 1 in (2.5 cm) of the soil samples.

Morro manzanita is expected to be relatively long-lived. Studies of stand age based on mink ring counts and aerial photos of previous disturbance events, including fire and possibly clearing, indicate that the youngest intact stands are about 37 years old; other stands are about 47 years old. The remainder are older than 47 years, with stands in the Elfin forest estimated to be the oldest.

The germination response of Morro manzanita to fire has not been studied in depth. However studies of other species suggest that fire intensity and depth of the buried soil seedbank influence the number of seeds that survive the fire and are able to germinate. Studies of post-fire establishment in other chaparral species suggest that the highest mortality occurs in seedlings during the first year following a fire. At this stage, the seedlings are young and are particularly susceptible to herbivory and to competition for water.

Some seedling establishment in Morro manzanita has also occurred following mechanical clearing. While the process of clearing likely causes some seed scarification, other environmental conditions that may encourage regeneration after a fire, such as heat and leachate from ash, are missing. Aerial photo analysis suggests that mechanical clearing and burning for ordnance removal in the 1940s and 1950s converted maritime chaparral containing Morro manzanita into weedy coastal sage scrub on what is now state park land west of Pecho Road.

Habitat

The distribution of Morro manzanita is correlated with that of soils, classified in soil surveys as Bay-wood fine sands, developed on ancient sand dunes that were deposited during the Pleistocene epoch, when sea levels 300 ft (91.4 m) lower than current levels allowed large volumes of sand to blow inland into the Los Osos Valley. Morro manzanita is found in association with coastal scrub, maritime chaparral, and coast live oak woodland communities in sites with no or low to moderate slopes. On steeper slopes, particularly on the north-facing slopes of the Irish Hills, Morro manzanita occurs in almost pure stands.

Where Morro manzanita occurs in dense stands, few understory species are present. Morro manzanita is not known to inhibit the growth or seed germination of other plants (allelopathic), but allelopathy is known in at least one other species of manzanita. Older individuals of Morro manzanita may have canopies 33 ft (10 m) in diameter.

Distribution

The historic distribution of Morro manzanita was estimated to cover between 2,000 and 2,700 acres (809.4 and 1,092.7 hectares), based on the distribution of Baywood fine sands soil in the Los Osos area. The flat areas covered by Baywood fine sands have largely been developed, primarily in the communities of Los Osos, Baywood Park, and Cuesta-by-the-Sea on the south and east sides of Morro Bay. Some development has also occurred on the steeper north-facing slopes of the Irish Hills. The current range of Morro manzanita is approximately 840-890 acres (339.9-360.2 hectares); half of the range consists of small or low-density patches of manzanita plants that remain in and around developed areas of Los Osos and Baywood Park, and half consists of more continuous and more dense stands of manzanita. An analysis of mapped distributions by cover classes suggests that the area actually covered by Morro manzanita shrubs may currently be less than 400 acres (161.9 hectares). Population estimates from 1992 range from 86,000 to 153,000 individuals, depending on the method used.

Approximately 65% of the remaining Morro manzanita habitat is in private ownership; the bulk of this is habitat with high densities of manzanita. Approximately 35% of the plant's habitat is on publicly owned lands within Montafia de Oro State Park, and two small preserves managed by California Department of Fish and Game; most of the habitat on public lands supports low or moderate densities of Morro manzanita.

Threats

The greatest threat to Morro manzanita is loss and fragmentation of its habitat from development. About 75% of its historical habitat has been altered by development, primarily in the communities of the Los Osos area. Over half the remaining habitat is in private ownership; proposals are pending to develop several large parcels.

Although approximately a third of the habitat for Morro manzanita is owned and managed by the California Department of Parks and Recreation, it is still subject to alteration. Groves of non-native Eucalyptus trees planted in the early 1900s have encroached on nearby stands of Morro manzanita. The Department initiated a stand containment project in 1989, which removed seedling trees that were established beyond the perimeter of the original groves. Current efforts are focused upon removal within the Hazard Canyon riparian corridor. However, if the containment project is not maintained, new expansion of the Eucalyptus into manzanita habitat can be anticipated. Also within Montafia de Oro State Park, installation of a trans-Pacific telephone cable resulted in the removal of approximately 300 plants in Hazard Canyon in the early 1990s. Planning averted greater destruction.

Except for two parcels owned by the California Department of Fish and Game, the remaining habitat for Morro manzanita is in private ownership on lands that surround the communities of Baywood Park and Los Osos. Expansion of these communities has already destroyed Morro manzanita habitat, and much of what remains is slated for residential development.

Conservation and Recovery

In response to a petition to the State of California to list Morro manzanita as a threatened species, the California Coastal Conservancy funded the Land Conservancy of San Luis Obispo to develop conservation strategies for the state and federally endangered Morro Bay kangaroo rat as well as for sensitive species, including the Morro manzanita. The Conservancy has been developing strategies in conjunction with the Service, California Department of Fish and Game, the California Department of Parks and Recreation, local and county planning agencies, and local landowners. To date, such efforts have been hampered by conflicting goals among the participating entities and lack of participation by key landowners. Legally binding conservation measures that would afford protection to the Morro manzanita have not been developed, while proposed real estate developments located in high density manzanita stands are being approved by elected County officials.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
(503) 231-6121
http://pacific.fws.gov/

Reference

U.S. Fish and Wildlife Service. 1998. "Recovery Plan for Morro Shoulderband Snail and Four Plants from Western San Luis Obispo County, California." U.S. Fish and Wildlife Service, Portland, Oregon. 75 pp.