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

<http://calflora.org/cgi-bin/specieslist.cgi?countylist=any&namesoup=arctostaphylos&plantcomm=any&format=photos&orderby=taxon>

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

<http://www.eoearth.org/view/article/150218/>

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.

Milkweed Magic

Driving around in the lower elevations of Tejon Ranch in the hot days of mid summer feels a bit like being a flea on the flank of a lion--forever surrounded by broad rolling contours of golden brown. While most lower-elevation herbaceous plants have senesced at this time of year, there is a notable exception-- milkweeds! Poking through the gold in contrasting verdant green, one may commonly observe clusters of these extravagantly thick, broad-leaved herbaceous plants.

Milkweeds are one of our few species flowering in the hot dry of summer and thus are a fascinating powerhouse of faunal activity. Lingering by a cluster of flowering plants for a few moments reveals a buzzing maelstrom of invertebrate species coming in to feed from the dense clusters of blossoms. Many of these species have evolved to rely specifically on milkweed for part of their life cycles.

Tarantula hawks (Pepsis sp.) left, and unknown thread-waisted wasp (suspected Podalonia sp.) right, feeding on narrow leaf milkweed (Asclepias fascicularis). Observed in lower elevation grasslands in the San Joaquin Valley, Tejon Ranch.

Milkweeds are so named for their potent milky sap, easily observed when a leaf or stem is broken. The chemical structure of the sap contains steroids called cardenolides which are highly toxic to most living things. There are some species, however, who have developed resistance to the toxic effects of cardenolides, and are brilliantly adapted to sequester these compounds in their own tissues as a personal defense against predation. In ecology, this adaptive trait is called aposematism, and is commonly advertised by bright coloration that warns predators of a distasteful or sick-inducing would-be meal. Here on Tejon Ranch, we have observed several milkweed associate species that exhibit aposematism. Below are a few examples:

Large milkweed bug nymphs (Oncopeltus fasciatus). Observed west of Los Alamos Canyon in the Antelope Valley, Tejon Ranch, feeding on narrow leaf milkweed (Asclepias fascicularis). Both nymphs and adults feed on various species of milkweeds.

Milkweed aphids (Aphis nerii) feeding on desert milkweed (Asclepias erosa). These aphids were apparently introduced from Europe. Observed in various locations in the San Joaquin Valley, Tejon Ranch. All individuals are female and they reproduce by giving birth to live young that are clones.

Milkweed longhorn beetle (suspected Tetraopes basalis) feeding on desert milkweed (Asclepias erosa). Observed in Tunis Canyon in the San Joaquin Valley, Tejon Ranch. Adults and larvae feed on milkweed vegetation. In order to avoid being inundated by the copious toxic and sticky sap, this beetle will cut one or more incisions in the mid-vein of the leaf and forage on the vegetation after the cut(s) have slowed the flow of thick sap. Pretty smart!

Desert milkweed (Asclepias erosa)

 In California we have about 15 native species in the milkweed genus Asclepias (family Apocynaceae). Four of these can be found on Tejon Ranch and are generally distinguished by their erect stature, opposite or sometimes whorled leaves, and unique, highly specialized flower structure. 

California milkweed (Asclepias californica)

Queen butterfly (Danaus gilippus). Larval form require milkweeds. 

This individual was observed in the eastern Mojave Desert on

 Mojave milkweed (Asclepias nyctaginifolia), a CNPS list 2B.1

 species (rare, threatened, or endangered in California).

A renowned aposematic species with a well-documented obligate relationship to milkweeds are monarch butterflies (Danaus plexippus). The life story of the monarch rivals the most riveting and inspiring of dramas—a journey involving several generations traversing international borders for thousands of miles in a perfectly timed and geographically specific cycle relying on countless impossible ecological pieces. Perhaps the most critical piece to their survivorship involves milkweeds--monarch adults lay their eggs on milkweeds and it is the larvae that ingest the plant material, ensuring that the vivid and vulnerable adult travelers are protected from predators on their long journey. They are one of several butterfly species who depend on milkweeds for their reproductive success. Declining milkweed populations throughout the Americas due to the loss of habitat from development and cropland conversion has been implicated in severely decreasing monarch populations—estimated at a more than 80% reduction in their population since the 1990s. In fact, monarchs are currently under review by the US Fish and Wildlife Service to determine if their declining populations warrant protection under the Endangered Species Act. There are many efforts being made to educate the public about the importance of preserving milkweed populations and to encourage the planting of native milkweed species. 

So next time you find yourself near a patch of these magic plants, take a moment to observe the extraordinary diversity of life that they support and appreciate the complicated stories they are central to. Consider doing your part to support these important plants--for the myriad species that have spent millennia evolving unique characteristics with milkweeds, as well as those that flourish foraging from the high summer flowers. Here are some ways to learn more and to help out:  

An informative guide to select California milkweeds:

http://www.xerces.org/wp-content/uploads/2011/10/CA-milkweed-guide_XercesSoc6.pdf

 A coalition of agencies and organizations focused on monarch conservation:
http://monarchjointventure.org/get-involved/create-habitat-for-monarchs/

 A non-profit organization dedicated to conserving invertebrates and their habitat:

 http://www.xerces.org/

References

Munroe, Lynne and Gene. 2013. Desert Insects & Kin of Southern California. Lyons, Colorado: Merryleaf Press.

Morhardt, Sia and Emil. 2004. California Desert Flowers: An Introduction to Families, Genera, and Species. Berkeley and Los Angeles, California: University of California Press.

Project Milkweed. The Xerces Society for Invertebrate Conservation. Portland, Oregon. Accessed 20 July 2015. <www.xerces.org/milkweed>