Pallid Manzanita

Pallid Manzanita

Catherine AhSam

Dr. Needles

Bio 227

Manzanita, January Bee Plant of the Month

Organism Description and Ecology

Arctostaphylos pallida, also commonly referred to as Pallid Manzanita, is a shrub requiring specialized environmental conditions that only the fog and climate of the Bay Area can provide for the 1,353 mature A. pallida plants left in the world. Pallid Manzanita is a fairly new endemic species of Arctostaphylos described in 1933. Prior to that, Arctostaphylos pallida was mistakenly determined as Arctostaphylos andersonii in a sample collected in 1902 from the East Oakland Hills. Controversy sparked amongst the scientists as to whether A. pallida was a distinct species, but no taxonomic alterations were made in taxonomic literature and A. pallida is documented as a full-fledged species to this day. 

Over 100 species exist within the Arctostaphylos genus, and the most diverse populations of Arctostaphylos (30 species to be exact) occur along the coast of California, spanning from Mendocino County to San Luis Obispo County. Species allocation depends on local soil types, microclimates, and fire frequency.

A. pallida finds its niche in frequent summer fog as a maritime chaparral, and establishes itself on relatively cool, moist, and stable locations within 11 kilometers of the San Francisco Bay. Shade is detrimental to this shrub and is acquired to a specific fire regime which accomplishes seed dispersal. A. pallida is an upright evergreen shrub that grows up to 13 feet with rough, gray or red bark. Its twigs are covered with fine white hairs making them candescent, its leaves are one to two inches, pale green, and grow closely together so that they are overlapping. Flowers are white, rose, or light rose, urn-shaped, 0.2 to 0.3 inches long, and occur from December to March. Fruits are 0.3 to 0.4 inches long, spherical, and sticky to the touch.

Geographic and Population Changes

As stated before, the first sample recorded of A. pallida was harvested in 1902 in the East Oakland Hills. Researchers pursued this population in 1933 and found that there was a second population on the hills behind Piedmont of Alameda County. A third population was reported in the 1940’s or 1950’s in Sobrante Ridge of Contra Costa County. James Roof, the founding director of East Bay Regional Parks District’s Tilden Regional Park Botanical Garden, had planted several dozen A. pallida between 1939 and 1940 along Shasta Road and Gold Course Drive in Tilden Park.

Today, there are only two areas that house naturally occurring populations of A. pallida: Huckleberry Ridge (Alameda County) and Sobrante Ridge (Contra Costa County) at an elevation between 656 to 1,460 feet.  It is possible that the range in between these two geographic locations bank dormant yet viable A. pallida seeds. Additionally, the two populations that Roof planted in 1939 are still present in Tilden Park, as well as random A. pallidas growing in Joaquin Miller Park, because of soil disturbance or controlled fire conducted in the park. 

The largest population occurs on Huckleberry Ridge among the satellite stands. There was a total of 2,400 to 2,700 A. pallida that had habituated Huckleberry Ridge in the mid-1980’s. A complete census of A.pallida was finished in 2004 which revealed that only 747 mature shrubs remained in the area and 325 shrubs occupied the Huckleberry preserve, 326 occurred close to homes adjacent to the preserve, and 96 on a tennis club’s property. The Manzanita Flat population in Joaquin Miller Park was established by means of homebuilding crews unknowingly transporting seeds to the site, but these A. padilla have now been extirpated by goat vegetative clearing efforts.

Sobrante Ridge Regional Preserve

Phytophthora cinnamomi

Listing Date and Type of Listing

A. padilla was listed as endangered in California in November of 1979 and threatened throughout its range on April 22, 1998. A. padilla was listed for habitat destruction due to home development, disease, and manmade implications. A. padilla was also given a recovery priority number of 5 which implies that the species is extremely threatened and has little chance to recover because of the rising number of threats. 

Cause of Listing and Main Threats

There is a surprising abundance of threats that hinder the success of A. padilla. The main challenge being the expanding urbanization of communities. One third of the A. padilla population occurs in the backyards of homes or close to such homes. As a result, the shrubs are considered a fire hazard and are removed to reduce fuel supply in the case of a fire. The second big player in A. padilla mortality is the incurable non-native, soil-borne fungal pathogen, Phytophthora cinnamomi, which has caused mortality in Huckleberry Preserve and the Big Trees Trail stands. Phytophthora cinnamomi has targeted multiple species of shrubs and chaparrals, even ran the Coast Live Oak to extinction in the East Bay Hills. This pathogen disintegrates the root system, and so infected plants become dehydrated causing beneficial pathogens to take on antagonistic effects without proper water intake and retainment on the plant’s behalf. Phytophthora cinnamomi is contracted through soil transporting vectors such as car tires, shoes, tools, and ambulance of humans, although sheer human activity like walking, biking, and driving proves to be the biggest contributing factor of disease transmission. This disease has no cure and can persist in the soil without a host so long as the pathogen can emit spores.

Phytophthora cinnomomi

 Another issue for A. padilla is competition for sunlight with neighboring vegetative communities. A. padilla is highly shade intolerant and deteriorates gradually in the presence of competition for sun, as well as space. Specifically, larger trees are creating a canopy of shade, killing the A. padilla underneath their shadows. Vegetation clearing tasked by goats outright reduce the population of A. padilla, but such actions do not allow the soil to create a viable seed bank to regenerate. Lastly, Mother Nature administers small fires on a regular basis to stimulate plant regeneration, but humans have suppressed fires. In doing so, humans have increased fuel stocks, encouraged larger and more intense fire, which scorch the earth and kill the seed banks as well as any other vegetation. 

Recovery Plan

The main target to be addressed in the recovery plan is to ensure to maximize seed production and seed banks to replace mature plants in the case of a fire. Along with an adequate seed supply, the spread of Phytophthora cinnamomi needs to minimized and infected plants need to be treated. Native and non-native vegetation that creates shade over A. padilla will be managed, populations of A. padilla will be aggrandized, more area will be occupied by A. padilla, and assurance that populations are protected from wildfire reduction efforts is also significant in the species’s recovery.

Personal Action

On the public’s part, the only way to help A. padilla populations is to tolerate the shrub’s presence on one’s property. Park officials and wildlife conservationists will oversee fire regime, shading, competition, etc.

More Sources

Sobrante Ridge Regional Preserve - Preserve that is home to A. padilla

Works Cited

"Manzanita, January Bee Plant of the Month." The Bee Gardener. UC Davis Honey Bee Haven. Web. 30 Nov. 2015.

"Phytophthora cinnamomi." California Forest Pest Control. California Forest Pest Control. Web. 30 Nov. 2015. 

Recovery Plan for Arctostaphylos pallida (pallid manzanita). Sacramento, California. U.S. Fish and Wildlife Service, 2015. Web. 30 Nov. 2015.

“Sobrante Ridge Regional Preserve.”  East Bay Regional Park District. East Bay Regional Park. Web. 30 Nov. 2015.