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Wednesday, December 2, 2015

Much Ado About Manzanitas, by Scot Pipkin Public Access Manager


A stately big berry manzanita (Arctostaphylos glauca) grows in the southern foothills of the Tehachapi Mountains


As a native San Diegan, people I meet often assume that I am a surfer. It’s not true. During my formative years, I was more likely found hiking the hills of “East County” SD than getting barreled off the Point. Part of what attracted me to the granite-studded mountains was the fantastic chaparral vegetation that grew in between rock piles. In particular, I was always struck by the stark beauty of manzanitas (Arctostaphylos sp) with their ribbon-like bark making intricate patterns on their branches. Anyone throughout the West who has tried bushwhacking in manzanita country has certainly developed a healthy respect for these plant’s toughness. 
Leaves and flower buds of A. glandulosa gabrielensis
Like many other taxonomic groups, California boasts an incredible diversity of manzanitas. Of an estimated 109 species worldwide (Encyclopedia of Earth (http://www.eoearth.org/view/article/150218/), California is home to about 62 and many subspecies (http://alturl.com/6yno3). Looking at the evolutionary history of Arctostaphylos, it appears to have evolved around 15 million years ago, with a big diversification occurring 1.5 million years ago (http://www.cnps.org/cnps/publications/fremontia/Fremontia_Vol35-No4.pdf#page=10). The recent explosion in California manzanita species seems to be associated with shifts in statewide geology due to faulting and volcanism (ibid). The Mediterranean climate of California has probably further supported the success of this group as their leathery leaves, hairs, and other features support water retention during long dry periods. 


This time of year, naturalists can observe firsthand why spring technically occurs in California in fall. Manzanitas are currently setting their nascent flowering structures, timed to the historic start of California’s rainy season: October/November. Apparently, these structures are a definitive tool for accurately identifying California manzanitas (J. Keeley, pers comm). Indeed, a quick survey of manzanita species of the region reveals extremely diverse flowering structures.  


 
Leaves and flower buds of A. glandulosa cushingiana
Leaves and flower buds of A. glauca























Sandy soils tend to be better habitat for A. glandulosa cushingiana than other species
On Tejon Ranch, there are five (potentially six) different manzanitas including: A. glandulosa cushingiana, A. glandulosa gabrielensis, (and possible A. glandulosa mollis), A. glauca, A. parryana parryana, and A. viscida viscida. With the help of Dr. Brandon Pratt from Cal State Bakersfield and Dr. Jon Keeley of the USGS, the Conservancy recently identified that two subspecies, and possibly a third, of A. glandulosa are on the property. This is particularly exciting, because San Gabriel manzanita (A. glandulosa gabrielensis) one of the subspecies confirmed on the Ranch is listed as a rare plant by the California Native Plant Society.  

Habitat for A. glandulosa gabrielensis and A. glauca in the Antelope Valley on Tejon Ranch
Members of Arctostaphylos like life on the margins. From the well-known bearberry/kinnikinik/Arctostaphylos uva-ursi in the polar and alpine regions, to the extremely dry mountains of North America’s deserts, manzanitas are hearty survivors. Here in California, fire appears to have a major influence on species morphology and ecology as well as arid climate conditions. Generally, there are two types of responses that plants can have to successfully perpetuate after a fire. Some are “seeders” meaning future propagation of the plant is dependent on successful germination from the seed bed. In certain cases, the seeds of these plants can lie dormant for decades until the heat or chemical changes of a fire activate the germination process. Other plants are “resprouters” after a fire, meaning they have a dense root ball or burl that creates new growth following a fire. 



Big berry manzanita (A. glauca) is a "seeder" and tends to have a trunk
In manzanitas, both strategies are employed. Some species, such as the widespread big berry manzanita Arctostaphylos glauca, rely on the seedbank for reproduction. After a fire, most mature A. glauca individuals are likely to be scorched. New individuals will germinate from seeds in the ground and the plant’s survival in that area will be assured. In contrast, other species such as Arctostaphylos glandulosa form underground structures that survive the fire and allow the plant to resprout following the disturbance. A great deal of work has been done to better understand the ecological and evolutionary implications of these two strategies, which are quite fascinating. http://www.werc.usgs.gov/OLDsitedata/seki/pdfs/amn1.pdf, http://www.werc.usgs.gov/OLDsitedata/seki/pdfs/amn4.pdf

A. glandulosa is a "sprouter" and has a burl at its base

 
On Tejon Ranch and throughout southern California, work is being done to better understand drought response in chaparral plants. Being dominant members of these habitats, manzanitas play a significant role in these studies. As it turns out, the two growth strategies of Arctostaphylos have implications for plant survival during drought. Seeders tend to have more shallow root systems and appear to be more susceptible to drought effects, whereas sprouters have more well-developed root systems and tend to buffer drought more effectively (B. Pratt, pers comm). 


Right now, researchers and students from Cal State Bakersfield and Pepperdine University are looking at chaparral plants on Tejon Ranch (and throughout the region) to better understand how different life history strategies respond to drought. Hopefully, this information will help land managers like Tejon Ranch Conservancy understand the complex dynamics of these systems and ultimately provide us with insight about managing them in the face of climate change. 


References:  

Calflora. "Arctostaphylos" 2 December, 2015

Hogan, Michael C. "Arctostaphylos" 2 December, 2015

Keeley, Jon E. and Zedler, Paul H. "Reproduction of Chaparral Shrubs After Fire: A Comparison of Sprouting and Seeding Strategies" American Midland Naturalist 99, no. 1 (1978): 142-161

Keeley, Jon E. and Keeley, Sterling C. "Energy Allocation Patterns of a Sprouting and a Nonsprouting Species of Arctostaphylos in the California Chaparral." American Midland Naturalist, no. 1 (1977): 1-10

Parker, Thomas V. "Diversity and Evolution of Arctostaphylos and Ceanothus." Fremontia 35, no. 4 (2007): 8-11



About the Author:

Scot Pipkin is the Public Access Manager for Tejon Ranch Conservancy. He lives in Pine Mountain Club with his wife and two-year-old daughter, and enjoys natural history, art, music, and riding bicycles.