Manzanita on the Rocks
Soils and Manzanita Diversity
As can be seen in the photo by Tom Barr above, manzanitas (genus Arctostaphylos) are remarkably adaptable.
Manzanita shrubs are a major component of the montane chaparral community, growing in granitic soils above 4500 feet with an average annual rainfall over 35 inches, as well as in sandy soils found in the southern maritime chaparral of Del Mar, California, with an average annual rainfall of 12 inches.
The threatened endemic Ione manzanita (Artostaphylos myrtifolia) is mostly restricted to a narrow corridor in Amador County, California, where it grows in acidic soils with high aluminum content (see images below).
Within a 22 mile diameter circle, centered near San Luis Obispo on California’s central coast, one can find seven localized endemic species of manzanita (Arctostaphylos obispoensis, A. pilosula, A. luciana, A. rudis, A. pechoensis, A. osoensis, and A. morroensis). Similar to Ione manzanita, these seven species are confined to edaphic “islands,” outcroppings of particular soil types (serpentine, Monterey shale, granitic, and Pleistocene sands) where chaparral is typically found among a landscape of forest, coastal scrub, and grassland. See map.
These islands may have served as genetic reservoirs for the genus, with different species migrating onto and off the soils during the numerous Ice Ages.
Map from Field Guide to Manzanitas by Kauffmann, Parker, Vasey (2015).
Del Mar manzanita (Arctostaphylos glandulosa subspecies crassifolia) grows in nutrient poor sandstone soils in coastal San Diego County. It is a federally listed Endangered Species.
Dr. Tom Parker and his loyal companion, Trinity, take photographs of Glossyleaf manzanita (Arctostaphylos sensitiva) growing on sand dune deposits at the Bonny Doon Ecological Reserve near Santa Cruz, California.
Additional References on Manzanita Diversification
Parker, V. T. 2007. Diversity and Evolution of Arctostaphylos and Ceanothus. Fremontia 35 (4): 8-11
Vasey, M.C. and V.T. Parker. 2014. Drivers of diversity in evergreen woody plant lineages experiencing canopy fire regimes in Mediterranean-type climate regions. In Plant Ecology and Evolution in Harsh Enviroments. Eds: N. Rjakaruna, R.S. Boyd, and T.B. Harris. Nova Science Publishers Inc., New York.
Vasey, M.C., V. T. Parker, K. D. Holl, M.E. Loik, and S. Hiatt. 2014. Maritime climate influence on chaparral composition and diversity in the coast range of central California. Ecology and Evolution. Open Access.
Parker, V.T. and M.C. Vasey. 2016. Two new subspecies of Arctostaphylos (Ericaceae) from California and implication for understanding diversification in this genus. Madrono 63 (3): 283-291.
Tom Parker and Mike Vasey, manzanita experts par excellence. More from Dr. Parker and the amazing midnight marauders here.
Ione manzanita adapts to hostile soils
Growing in oxisol soil rarely found outside of tropical areas, the Endangered Ione manzanita (Arctostaphylos myrtifolia) survives on a geologic island of about 1,000 acres in north central California. Oxisols have high concentrations of iron and aluminum oxides and hydroxides, hence their characteristic reddish - yellowish colors. The Endangered Ione buckwheat (Erigonium apricum) is also restricted to this area.
The tiny leaves of Ione manzanita (Arctostaphylos myrtifolia) and the red nascent Inflorescences (early flower buds) catch the early morning light.
The extremely hard "ironstone" covering of the Ione soil deposit makes it difficult for plants to establish themselves. Here is an Ione manzanita (Arctostaphylos myrtifolia) struggling to gain a foothold.
The strange, sandy terrain of the Ione region. The primary material being mined was lignite (a form of coal) that contained montan wax that was used in making carbon paper, phonograph records, polishes, and a rubber wax used for industrial purposes. Also, silica and quartz sands from the white kaolinite were extracted here.
Pollution from surface mining in the Ione area colors water deposits that have collected in open mining pits a light blue. The white deposit is kaolinite, high in aluminum and silica. In the foreground is whiteleaf manzanita (Arctostaphylos viscida). Arctostaphylos manzanita is nearby on more normal soils mixed with oaks.
Fungal infections are causing havoc for Ione manzanitas. A branch canker caused by a species of Fusicoccum, including F. aesculi, causes some mortality. But it's the root and crown rot caused by Phytophthora cinnamomi that's responsible for destroying entire stands of Ione manzanita, preventing its regrowth in patches of infested soil. Note dying shrubs and bare soil.
A healthy stand of Ione manzanita.