In 1998 I first visited the Channel Islands. This was early in my naturalist career but I was struck, none-the-less, by the beauty and isolation I found on Santa Cruz Island. On that trip I first saw the endemic island scrub jay (Aphelocoma insularis) and began to develop an understanding and interest in island biogeography. Twenty years later this experience brought me to Santa Rosa Island–in major part to see the Torrey pine grove–but also for the opportunity to explore one of the least visited places in Southern California.
Santa Rosa Island is separated from the mainland by over 25 miles of water. The next closest landmass is San Miguel, which is now isolated from Santa Rosa by three miles of water. Isolation has nurtured endemism on both a localized island level as well as on a unifying level between islands. Combined, all the Channel Islands are home to 150 species of unique plants and animals. Santa Rosa hosts 46 of those, including six endemic plants that grow nowhere else.
My elegant crossing Tule Creek. Photo by Josh Smith.
Last weekend, I hiked in Trinity County along a low-elevation, fire-prone section of the Bigfoot Trail between Highway 3 and Hayfork and was able to witness obligate & facultative seeding in action.
One-third of manzanita species are facultative seeders. These are species that regenerate post-fire by both seed and burl resprouting. The remainder are obligate seeders that lose their entire adult population in a fire and depend on a seed bank for regeneration. Obligate seeding is the current model in manzanita evolution.
To understand why, consider the climatic dynamics over thousands, or tens of thousands of years or more. In the case of the resprouting species, particular individuals can live for centuries, resprouting over and over, cloning new individuals as the burls expand with each fire cycle. But in that population, the rate of genetic change is limited, because most individuals live a long time by way of asexual reproduction. This suggests that populations may be unable to respond to rapid climatic changes that might occur in only hundreds of years. The obligate seeders, on the other hand, lose all adults in stand-replacing fires and new post-fire generations have to establish from more genetically diverse seeds. Those populations consequently have greater flexibility to shift and adjust as circumstances require; traits that might have been rare and less important in older generations can emerge through natural selection and become critical in the newer generations within the lifetime of resprouting manzanitas.
Much of this area burned in the summer of 2015. While evidence of the fires were everywhere, there are many signs of the next generation of plants returning to the landscape. This was particularly true on some of the south-facing slopes above Philpot Campground where two species of manzanitas were exploring different reproductive regimes– both obligate & facultative seeding.
Arctostaphylos manzanita is a facultatative seeder. It can resprout by seed but also from dormant buds. When present, these structures are often prominent and are called burls (also ligno tubers)–seen in the middle of the sprouting leaves.
Arctostaphylos canescens is an obligate seeder and does not have a burl. Instead, genetically unique seedlings resprout from a well-stocked seed bank.
Botanical Wonders of the San Gabriel Mountains National Monument.
Manzanitas are most commonly found across the Angeles National Forest on south-facing slopes where they are restricted to various mineral soils (most often granites). A. glandulosa appears in the front range from ~2,000-5,000 feet, A. patula in the higher elevations above ~7,000, A. parryana on the north slopes toward the Mojave from ~5,000-7,500, and A. glauca is common across the range but mostly on the north slopes adjacent to the Mojave from ~4,000-6,000. I never found Arctostaphylos pungens but it is within the range according to various sources.
What follows is a photographic journey through the San Gabriel Mountains to enjoy the spectacular places manzanitas grow.
Arctostaphylos glandulosa ssp. gabrielensis decorate the beginning of the Devil’s Canyon trail near Chilao Flat.
One of the most interesting geologic stories in western North America is told by the ultramafic rocks that were formed deep in the ocean floor. As the Pacific Plate collided and dove beneath (subduction) the North American Plate, the bottom layers from deep oceanic mantle were scraped (obduction) onto the North American Plate. These depositions are referred to as ophiolites and the Klamath Mountains present some of the most extensive examples on Earth.
Serpentines of the High Divide with Jeffrey Pine and Knight’s Pinemat Manzanita in the foreground– by John O. Sawyer.
Manzanitas of San Bruno Mountain County Park – An island of Artctostaphylos endemism
This region is the epicenter for “localized endemism” in manzanitas. Two manzanita species are found on this mountain and nowhere else (A. pacifica and imbricata) and both share space and time with a distinct form of bear-berry (A. uva-ursi), the equally rare Montara Mountain manzanita (A. montaraensis) and the more common brittleleaf manzanita (A. crustacea). The San Francisco Bay area is at the center of the range of biodiversity for the genus Arctostaphylos–which extends from just north of the Oregon-California border southward to northern Baja California, Mexico. Other nearby Bay Area rarities include the Franciscan manzanita (A. franciscana), Presidio manzanita (A. montana ssp. ravenii), and Marin manzanita (A. virgata) to name a few.
Downtown San Francisco, seen from San Bruno Mountain County Park.
In the California Floristic Province, the genus Arctostaphylos is a particularly fine illustration of how long-term dispersal events lead to colonization and consequent adaptive radiation in a group of plants. Fossil records show that this genus has been migrating and adapting to climatic shifts for at least 15 million years. However, only in the past few million years has Arctostaphylos, commonly called manzanita for its berries’ resemblance to small apples, found its promised land. The California Floristic Province’s exceptionally diverse range of habitats, particularly of ones that provide a taste of the suboptimal, is perfect for manzanitas. A synergistic mix of climate stability, soil variability, topographic volatility, and fire frequency provides the perfect alignment of biotic and abiotic factors. Like many other California evergreens (including my beloved conifers!) these hardy plants have benefited from inhospitable environments wherein competition from many plants is reduced and their own adaptability to poorer growing sites allows them to thrive. This, somewhat ironically, has made the unassuming “little apple” the most species-rich shrub genus in the California Floristic Province.
Arctostaphylos pilosula – an endemic species to the San Luis Obispo region.
Smokey Creek and South Fork Trinity River Along the Bigfoot Trail
Spring break offered the opportunity for a brief trip into the southern Klamath Mountains. The Bigfoot Trail was calling, and as I am working on a new map set for the trail, my goal was to check some of the route descriptions and enjoy the wilds of Trinity County. Our first significant snowfall of the rainy season locked me out of the Yolla Bolly-Middle Eel Wilderness with over a foot above 4000′. So the lower elevations of the South Fork Trinity River became my destination. Here I would re-explore the Smokey Creek Trail and enjoy some quality time with my new friend, the manzanita.
Jeffrey pine and common manzanita (A. manzanita) on a serpentine outcrop above the South Fork Trinity River.
I was recently asked by KHSU, here in Humboldt County, to write a two minute script for their Sound Ecology series. I chose to write about the conifers of the Klamath Mountains. I hope you enjoy this piece and are planning your next adventure into this botanical wonderland.
Here are the activities I will be a part of in the coming months, please join me!
