Sea mist supports a surprisingly diverse group of scrubby, brushy plants along California’s coast. Amy McDermott dives in. Illustrated by Yvonne Byers.

As the wind picks up, a light drizzle turns into a sideways-spitting rain on San Bruno Mountain, just south of San Francisco. Mike Vasey doesn’t seem to notice. He’s chipper and singularly focused, striding toward a shrub.

“Now look at this,” he says, leaning down to inspect the plant’s small spade-shaped leaves. “You can see how different it is from this other character.”

Vasey pulls a twig with ellipse-shaped leaves from his pocket and holds it up for comparison. He’s right. The two plants look very different, but they’re supposed to be the same species. They grow just a few hundred meters apart on this hillside. “These guys are both weirdos,” he laughs. “This is weirdo city up here.”

Vasey, a large man with a habit of wedging himself into tight thickets, directs the San Francisco Bay National Estuarine Research Reserve. He’s obsessed with a group of coastal plants called “maritime chaparral.” To the uninitiated, they all look dry and brownish, but Vasey has dedicated the better part of a decade to unraveling their surprising diversity.

California’s brushy seaside habitats, he has shown, contain far more plant species than their inland counterparts. For instance, about half of all species and subspecies of red-barked manzanita grow within 20 miles of the coast. Scientists know the chaparral is rich with species, but only in the last five years have they figured out why coastal habitats are more diverse: They’re shielded from the parching heat of summer by California’s coastal fog.

Islands of life

Chaparral is California’s hardy scrubland, but similar ecosystems have evolved in other Mediterranean climates. In South Africa, the scrub is called “fynbos”; in Chile, “matorral”; in Australia, “kwongan”; and in the Mediterranean, “maqui” or “macchia.” Each region has a different set of plant species, but they all face the same environmental pressures of hot arid summers, damp winters, and poor or shallow soils. That prompts tough, dense brush to evolve.

Even in California, not all chaparral is the same. Maritime chaparral is just one type, dominated by manzanitas and native wild lilacs (often called ceanothus). It pops up in small patches among grasslands, oak woodlands, and forests.

This ecosystem, found only in California and northern Mexico, hosts an abundance of rare native plants. They run the long, thin line between Mendocino and Baja, keeping to the lowlands and windward slopes of the Coast Ranges. Trails crisscross chaparral country, but few people get to know the thick and prickly brush. What looks like a sea of brown sameness conceals a whopping 105 different manzanita species and subspecies.

Maritime chaparral is humble. It’s easy to overlook this startling diversity because species aren’t all crammed on top of one another. Many grow in small geographic patches, popping up here and there for a few hundred square miles or less. Pajaro manzanita grows only in Monterey County, while Schreiber’s manzanita grows only in the Santa Cruz Mountains about 30 miles north.

Although one stand of chaparral might only have a few species, the diversity between these scattered islands of life is striking. Ecologists know the coast is rich with plant variety, but they have to zoom out to see just how rich.

“Everywhere you go, you get a slight variation,” says Brett Hall, director of the California Native Plant Program at the UC Santa Cruz Arboretum. He strides across a sprawling field on the campus, part of the arboretum’s native garden, then stops short at a clump of green-grey manzanitas.

“OK, this is a great one!” Hall says, resting an arm on one of the bushes. He treats this garden with the familiarity of his own backyard, because it is his backyard. Hall has lived and worked at UCSC since 1975, when he arrived as a student living out of his van in the arboretum’s parking lot. Now his white Subaru sits down a dirt trail in front of his house, built on the arboretum grounds.

The plant he’s leaning on is a Santa Lucia manzanita, he explains. It’s a pretty red-berried species that grows only in the southern Santa Lucia Mountains in San Luis Obispo County, on the east side of Highway 101. The soils change to the west, and the more widespread rounder-leaved Bishop manzanita appears. The Santa Lucia pops up “just basically along this one ridge,” Hall says. “And the [Bishop manzanita] is across the street.”

In the field, ecologists like Hall look for differences between flowers, fruits, and other characteristics to tell manzanitas apart. Their leaves vary in shape and size; soft hairs line some of them. Below the leaves, down their smooth (or sometimes rough and peeling) red limbs, some manzanitas also have a burl: a woody knot of dormant buds that “resprout after a disturbance,” Hall says with a grin. “Particularly fire… or a chainsaw, or a heavy pruning, or a bulldozer.”

Many species of manzanita depend on fire to burn their competitors. Then they begin their cycle of regrowth. Species that die during fires and resprouting species both have seeds that depend on heat or smoke to germinate.

Maritime chaparral plants are also interesting for the creatures that depend on them. Native birds, insects, and reptiles live in the dense briar. They support wood rats and other small mammals, as well as coyotes and bears that are known to eat the fruits. In the chaparral, Hall says, “you get this profound web of life.”

Up close, maritime chaparral is beautiful. The characteristic smooth red bark of manzanitas can twist into thick upright branches or curl squatly, like mat-forming ground cover. California lilacs bloom in a range of striking blues and purples, from milky mauve to dark velvet. But the tangle of the bush hides those subtleties from most passersby.

Unique as it is, maritime chaparral wasn’t on the scientific radar until the 1970s, Hall says. After the U.S. Endangered Species Act passed in 1973, there was a new push to name and protect rare species. James Griffin, a plant ecologist at the University of California’s Hastings Natural History Reservation in Carmel Valley, had worked in the maritime chaparral for years and saw the potential to name and protect this surprising diversity of rare plants along the coast. In 1978, Griffin was the first to describe the “maritime (or fog-belt) chaparral around Monterey Bay.” Griffin’s efforts paid off: In 1982, maritime chaparral fell under the umbrella of California’s Coastal Act as an “Environmentally Sensitive Habitat Area.”

Four years later, vegetation ecologist Robert Holland of the California Department of Fish and Game made an inventory of the state’s distinct ecosystems. Conservationists had begun to shift their focus from saving rare species to protecting whole habitats. Griffin had emphasized Monterey’s unique coastal plants, but Holland helped announce and confirm maritime chaparral as a unique ecosystem.

On the misty trail

Ecologists grew to recognize the rarity of plants in maritime chaparral, but they still didn’t know why there were so many rare species. Griffin’s “fog-belt” reference hinted at local climate as one influence. Twenty years would pass before scientists turned their attention directly to the fog.

In the early 1990s, UC Berkeley forest ecologist Todd Dawson tracked how fog affects California’s coastal groves of redwood trees. To study the towering giants, whose humidity and temperature vary from the light-flooded canopy to the musty forest floor, Dawson and his team climbed through the boughs. They installed fog water collectors in the trees’ skyscraper crowns and across the shaded understory.

Dawson found that 34% of the forests’ water came from condensation dripping off the redwoods. In the otherwise dry summers, 19% of the water within the giants—and a staggering 66% in the understory—came from fog. Over the next decade, Dawson and his research group found that redwoods, ferns, and many other forest plants absorb the misty moisture directly through their leaves. Without it, life would be much harder in groves along the coast.

If fog buffered the hot, dry summers in Pacific coastal forests, could it have the same impact on chaparral? Mike Vasey became intrigued by that question around 2007. He was in his late 50s and had worked in Bay Area conservation and manzanita taxonomy for many years. He was content, with one exception. “I told my wife, ‘I wish I’d gotten my Ph.D.,’” Vasey recalls. “She said, ‘Go get it.’”

So Vasey, a self-described “learning junkie,” enrolled at UCSC to pursue his doctorate. He wondered why so many rare manzanita species dotted the coast as members of maritime chaparral. It became the driving question of his dissertation. “That’s what really got me going,” he says. “I’m still going on that.”

From 2007 to 2012, manzanitas drew Vasey up and down the California coast from Santa Barbara to Sonoma. He set up 11 study sites at coastal lowlands, ocean-facing mountain slopes, and inland stands of chaparral. At each site, Vasey tested the manzanitas’ levels of water stress. He found that at the end of the dry season, there was a gradient ranging from mild stress along the coast to extreme stress in the interior. Coastal summer fog was the best explanation.

Vasey also examined patterns of chaparral diversity. He chose 87 random plots, each measuring 20 by 50 meters. He recorded the species growing in each plot, estimated their percent cover, and took soil samples to analyze. Using the GPS coordinates of each site, Vasey also downloaded climate data including temperature, precipitation, and relative humidity—a good surrogate for the frequency of clouds in summer.  He found that locally rare species, each in its own geographic pocket, create high diversity between manzanita stands, rather than many species concentrated in a single area.

The fieldwork wasn’t easy. “I got into some patches where I wondered if I would ever get out, it was so thick,” Vasey says. He didn’t carry a backpack or water—just a small hand trowel, a sample bag, and a field notebook in his back pocket. He could only wear floppy hats tied to his head. “I would go down into this chaparral with just what I could carry, just what I could push through.”

He didn’t always travel so lightly. On his first day out, Vasey was “better” prepared. He and a friend brought backpacks and measuring equipment. “Within 15 minutes,” he recalls, “we realized we just couldn’t get through it with all that stuff.”

So to measure his plots, Vasey had to get inventive. “Literally, listen to this,” he says, eyes glittering at the memory. “I had a piece of rebar with a little stopper on it, and a spool of rope with a really bright yellowish green softball on the end.” He would dive into the chaparral, ball in hand, to run the 50-meter-long rope over or through the packed-in scrub. “Any way I could get it through,” Vasey chuckles. “I crawled around in the chaparral for about 87 of those plots.”

He hoofed through miles of brush to understand why rare manzanitas and other species speckle the coast. After five years, Vasey had his answer. Of all the factors he considered, “really the climate issues were the biggest things,” he says. Cool, humid, foggy coastal lowlands and areas receiving more rain on coastal-facing slopes held the most species.

Vasey wasn’t surprised that fog is important for lowland chaparral stands near the sea. “In my mind’s eye, I was thinking this is a fog pattern,” he says. He expected that chaparral bathed in marine mists would hold the most rare species, because the wet conditions would dampen hot, dry summers—helping more plants survive.

But then Vasey found something unexpected: chaparral is also diverse on high windward slopes, far above the ocean’s fog. The mist burns off before making it up the mountainsides. Still, the rare plants hold on.

Winter rain was the wild card. When clouds blow in from the ocean, they are transformed by mountains. Ascending a slope squeezes out a cloud’s rain, dumping twice the amount of water on high windward slopes compared to coastal lowlands and interior uplands. So in summer, fog keeps the coastal foothills cool and damp, while in winter, extra rainfall quenches higher windward elevations. That extra water is the difference between life and death for many evergreen shrub species living on the edge in California's Mediterranean-type climate. Farther inland, chaparral has neither summer fog nor winter rain to ease the brutal dry season. Only a few tough species can survive.

Hot, dry inland habitats are “really a place only for the hardy and the brave,” Vasey says. “On the coastal uplands and lowlands between fog and rainfall, there's just a lot more opportunity for diversity to take hold.”

A foggy future

That opportunity could evaporate if the world’s changing climate burns off California’s coastal fog. Projections of rising temperatures point to a hotter and drier future, but scientists still aren’t sure what will happen to the mists. Fog might roll in more often, or it could dwindle away.

Many biologists, geologists, and climatologists are collaborating to predict the future of California’s fog. Alicia Torregrosa, a landscape ecologist with the U.S. Geological Survey, heads the Pacific Coastal Fog Team. The forecasts are challenging, she says, because mist forms around small unpredictable particles suspended in the atmosphere. Ocean salts, bacteria, “otter farts [or] any kind of gas, solid, or liquid particles” can act as tiny fog nuclei, she explains.

It’s hard to say how all those tiny particles will react as sea surface temperatures rise, ocean currents shift, and winds fluctuate. Hotter temperatures could burn off the fog faster than it dissipates today. But the heat could also evaporate more seawater, creating an even mistier seashore.

Torregrosa’s team is trying to develop models that account for all of these factors. For example, she’s setting up webcams to understand how quickly fog lifts as local temperatures change from morning to afternoon.

This research could one day help ecologists protect maritime chaparral, but crusaders like Hall and Vasey aren’t waiting around. They and other conservationists travel up and down the state, collecting seeds and cuttings from wild plants at risk. Members of the California Native Plant Society, in collaboration with UCSC and other institutions, are making a living library to ensure their beloved chaparral’s diversity won’t disappear.

At the UCSC Arboretum today, patches of manzanita and native lilac spring up in the 55-acre California Native Plant Garden. Rare species from San Luis Obispo grow beside Santa Cruz natives, as well as species ranging as far north as the Rogue River in southern Oregon and eastward into the Sierra Nevada. Still more plants lie dormant indoors; their seeds are dried and frozen.

One species at the arboretum, the Franciscan manzanita, is nearly extinct in the wild. It was native to San Francisco, but it disappeared in the 1940s. Then in 2009, botanists stumbled across the sole remaining plant on an off-ramp construction site near the Golden Gate Bridge. “There was just one,” Hall remembers. Local chaparral researchers took cuttings before the plant was relocated. Those cuttings now grow in botanical gardens around the Bay Area, including at UCSC.

For the Franciscan manzanita and rare species like it, life is getting harder. From a distance, the brush looks tough, but up close, it’s fragile. Just as researchers uncover why the chaparral is so diverse, they have realized it might die away. Conservatories and dedicated chaparral divers like Hall and Vasey are glimmers of hope for the shrubland clinging to the California coast.

© 2016 Amy McDermott / UC Santa Cruz Science Communication Program

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Biographies

Amy McDermott
B.S. (biology) University of California, Santa Cruz
M.A. (conservation biology) Columbia University
Internships: Science News, Grist

I’ve never been one for binaries. The world rarely operates in black and white. As a kid growing up in Southern California, I loved biology and the arts. They blurred together as I sketched our blue-gold agaves and the fence lizards skittering across our stucco garden walls. But in college, my diverse passions became a burden. I felt I had to specialize, to choose.

At 18, I chose marine ecology. Research took me from the velvety depths of the Monterey Trench to the sunlit shallows of Fiji. But without writing and art, I wasn’t whole.

As I deciphered the relationships between Melanesian reef fishes in grad school, I started an online science magazine. Telling visually driven stories restored my sense of balance. Now I don't have to pick among my passions. I choose them all.

Amy McDermott's website

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Yvonne Byers
B.A. (liberal studies) San Francisco State University
Internship: National Tropical Botanical Gardens, Kauai

Drifting up the coast from the warm waters of San Diego and landing on the foggy beaches in northern California, Yvonne has journeyed wide and far to find her true passions. After graduating San Francisco State University with a B.A. in liberal studies, she decided to travel to Hawaii and Central America where her love for nature only grew. Upon her return home she decided to attend the Science Illustration Program at California State University, Monterey Bay. Melding both her love for nature and art, the program helped her develop skills, community, and motive for her work. Yvonne is now ready to set foot in Hawaii, yet again, for her upcoming fall internship.

Yvonne Byers's website

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