Splendor in the Grass

By Sylvia Wright

Photos: Debbie Aldridge/UC Davis Mediaworks

Where do they come from? Where do they go? There’s much to be learned to help conservationists protect the disappearing vernal pools.

At just this time last year, on a ranch on the rolling eastern fringe of the Central Valley—private land where no surveyor’s stakes pierced the ground, no bulldozers had leveled the wetlands—UC Davis plant ecologists knelt in damp patches of spring flowers.

Nose-down in tiny white popcorn flowers, yellow goldfields, purple downingia and pink monkeyflowers, they called out their findings.

“Juncus capitatus.”
“Crassula aquatica.”
“Lasthenia fremontii.”
“Centunculus? Gratiola?”
“Lilaea scilloides.”

The litany of plant names was as much funeral dirge as ode to spring. Vernal-pool ecosystems such as this—seasonal pools and the slightly higher uplands that surround them—are among California’s most threatened landscapes.

Before European settlers arrived, vernal-pool ecosystems flourished on millions of acres throughout the state—in the Central Valley, atop volcanic flows and “table top” mountains on the western slopes of the Cascade Range and Sierra Nevada, on the terraces and bluffs of coastal Southern California and within the valleys of the Coast Range.

In the fall, the rains would fill these dry bowls, awakening millions of tiny animal eggs and plant seeds buried in the debris at the bottom. Through the winter, the pool would be a bustling community of microscopic plants and animals, fairy shrimp and tadpole shrimp, birds, bugs, beetles, frogs and toads, salamanders and snakes. Come spring, the drying pool would erupt in a grand finale of flowers, then roast in the summer sun until the rains returned.

Now, as much as 90 percent of vernal-pool ecosystems have been plowed under, paved over and built upon, and the losses continue. No one knows how many vernal-pool plants and animals have been lost permanently; 80 species are presently listed as threatened, endangered or of special concern. Hurrying to understand and preserve the remaining pool ecosystems, UC Davis researchers are studying many of their natural processes, including the movement of water in and out of pools, the distribution of vernal-pool plants, the needs of elusive tiger salamanders and the evolutionary bond between vernal-pool flowers and native solitary bees.

Michael Barbour, a UC Davis plant ecologist and professor of environmental horticulture, was coordinating the field botany on that day last spring. “There is great concern that we are running out of time to protect the vernal pools that are left,” he said. “To do that, we need to know much more about the nature of the plant and animal communities that make vernal pools what they are.”

The plumbing

Vernal pools typically form in surface depressions lying above an impermeable layer of clay, hardpan or rock. This pool of water is the foundation of the ecosystem—its defining feature—but little is known about how the water gets into the depression, why it stays and how it gets out. In December, UC Davis scientists began an extensive California study of vernal-pool plumbing.

Groundwater hydrologists Graham Fogg, a professor in the Department of Land, Air and Water Resources, and Thomas Harter, an associate UC Cooperative Extension specialist, and their research team are gathering hydrologic data from three representative sets of vernal pools in the Central Valley. Their two-year, $190,000 study is funded by the California Department of Transportation, which wants to know more about reducing the impact of road systems on vernal-pool habitat.

Harter said, “The questions we are asking include: Are these pools primarily fed by surface runoff or by water flowing into the pools from underground? Are there subsurface connections between some pools? And are there connections between the pools to shallow aquifers or even to the regional water table?

“The answers will help us better understand vernal-pool diversity—in size, shape and ecology—and appreciate the local hydrology’s role in the pool ecosystem.”

The plants

Vernal-pool plants sprout phoenix-like from seeds dropped into drying soils at the bottom of the pool in the previous spring, or even five, 10 or 30 springs ago. Species segregate according to preferred conditions: Dry-tolerant plants grow at the water’s edge; water-lovers concentrate in the pool’s deepest, wettest places; others fall in between. Their preferences produce “fairy rings” of successive blossoms. First come white meadowfoam and yellow carpet at the drier fringes, then goldfields and white popcorn flowers, and last, purple downingia and woolly marbles at the pool’s center.

Consulting biologist Carol Witham, an expert on California vernal-pool plants, worked with Michael Barbour last spring, helping assemble the first statewide classification of vernal-pool plant communities. “Throughout California’s history, people have been drawn to vernal pools because they are awesome splashes of color in the middle of grasslands,” Witham said. “They have 70 species of plants that grow no place else in the world—plants endemic to California vernal pools.”
Also on the plant-studies team were Bob Holland, an independent scientist and expert on vernal-pools geology and botany, who earned his master’s (’74) and doctor’s (’78) degrees in ecology at UC Davis; environmental consultant Rod Macdonald (M.S. ’78); and specialists from Russia, Spain and South Africa.

“We want to know which communities of plants are local and rare, which are widespread and common, and which are already protected in reserves,” Barbour said. “Then we will be able to say something about the threat of endangerment for each of these classes.”

The three-year study began last spring. On virtually every day in April and May, the botanists conducted knee botany, even belly botany, from dawn to dusk. When the advancing season had so parched the plants that it was impossible to do even “cadaver botany,” the team retreated to the Davis campus’s John Tucker Herbarium to sort specimens and analyze data.

Recently Barbour described their preliminary findings. He said they found a rich diversity of plant species, with an average of 35 species per pool. However, the combinations of species among pools did not vary as much as expected. There were about 17 combinations, or community types, Barbour said. “That’s good news. It should make it easier for agency biologists and non-botanists to understand the classifications and use our information for conservation.”

The bees

UC Davis entomology professor emeritus Robbin Thorp knows more about vernal-pool insects than anyone, and his discoveries have significantly expanded our conceptual boundaries of what constitutes a healthy vernal-pool ecosystem.

During his 38 years at UC Davis studying honeybee pollination in agriculture, Thorp squeezed in a great deal of observation of vernal-pool insects. He found that one group of native bees was particularly important—the specialist solitary bees. In a reproductive cycle evolutionarily synchronized with the spring bloom, solitary bees build underground nests in the drier uplands around the pools, then forage pollen exclusively from pool flowers to feed their offspring.

Thorp has shown these specialist solitary bees must have vernal-pool flowers. Is the need mutual? He says yes. “Solitary bees are certainly the most important pollinators for some flowers. There are a lot of other insects that visit those flowers, but specialist solitary bees are usually the most abundant visitors and the most efficient at transferring pollen from one plant to another.”

The salamanders

Photo courtesy of California Academy of Sciences

While Thorp’s bee research has underscored the need to protect vernal-pool uplands for the sake of pollination, studies of the California tiger salamander suggest that protecting the full suite of vernal-pool-dependent species will require preserving entire vernal-pool landscapes. Brad Shaffer, a UC Davis professor in the Section of Evolution and Ecology, has produced pioneering work on the biology and population genetics of California tiger salamanders. He has shown that the shiny black-and-gold salamanders need the wet pools to grow to maturity, mate and lay eggs, but when they are adults, they need the dry uplands for foraging.

Shaffer has been studying tiger salamanders intensively for 12 years. He has found that right about now, this year’s salamander tadpoles (properly called larvae) are gorging themselves on vernal-pool invertebrates such as fairy shrimp, water fleas and frog tadpoles. In the last rains of May, having metamorphosed from larvae to young adults, the salamanders will climb from the pools and spend the hot summer months in a rodent burrow up to 1,000 yards away from the pool itself. For the next few years, they’ll emerge from their burrows only in the rainy seasons, to feed on earthworms, plants, insects and pretty much anything they can catch. At age 5, the sexually mature salamanders will trundle back to a vernal pool and spawn the next generation.

Like Robbin Thorp’s findings on solitary bees, Shaffer’s discoveries about tiger salamanders have major conservation implications. “If you want to protect tiger salamanders, you’re going to have to protect not just the vernal pool but also a lot of the terrestrial habitat around the pool,” Shaffer said.

Another key question Shaffer has explored is whether there is more than one genetically distinct population segment of California tiger salamander. Genetic analysis shows, he says, that there are at least three. “So, now we’re coming to appreciate that there is more diversity of organisms in vernal pools than we ever knew, and that makes saving those examples of diversity even more important. We just weren’t aware of that at all 10 years ago.”

The future

Awareness has not always translated into preservation. Although vernal pools have received increasing amounts of protection under state and federal laws regarding wetlands and endangered species, “the fact is the remaining base of vernal pools and related ecosystems continues to decline,” said Tim Vendlinski, chief of the U.S. EPA’s regional wetlands regulatory office and a 1984 UC Davis alumnus. “As a regulator, I see proposed projects almost every day that will result in the further fragmentation and degradation of vernal pool resources.”

The largest intact vernal-pool complexes in the state, amounting to more than 90 percent of the total vernal-pool acreage, are on private ranchlands, said Bob Holland. Holland, Barbour, Carol Witham and many other scientists and vernal-pool advocates feel the best hope for vernal pools lies in those privately owned complexes. “My most recent maps show that most of the state’s remaining pools form a bathtub ring around the eastern edge of the valley,” Holland said. “That’s where there are the state’s thinnest, driest, oldest soils—those that are worst for agriculture and least well served by irrigation. They are ranch lands. Ranching is compatible with vernal pools—lots more so than tomato crops or houses. You can keep cows on a pasture for decades and still have nice vernal pools, but if you put one crop of corn in there one time, you’ll never have vernal pools again.”

In the past several years, non-governmental organizations such as The Nature Conservancy have catalyzed major conservation projects within the Central Valley resulting in the protection of tens of thousands of acres of vernal pool landscapes. The successful formula entails working with the ranching community to forge permanent land-use agreements that protect the natural resources while allowing ranching to continue.

One form of agreement, the conservation easement, has already safeguarded thousands of acres of pools in the state’s largest remaining vernal-pool landscape. Lying in the alluvial fan of the Merced River, in eastern Merced County, this complex comprises about 100,000 acres, including the Flying M Ranch. Beginning in the early 1980s, Flying M owners John and Lucia Myers and The Nature Conservancy worked out easements that now protect more than 5,000 acres. The Nature Conservancy hopes to eventually have 60,000 acres in eastern Merced under such easements.

Another large, private, pool-covered property in the Merced fan complex, owned by the Virginia Smith Trust, was named in 1995 as the site of a new University of California campus—just as UC Davis scientists and others were starting to detail the integration of vernal pools and vernal-pool uplands. In the many discussions that followed, “It became clear to the university that, although the proposed campus site was avoiding the pools themselves, it could conceivably affect the watershed for some of these pools,” said James Grant, UC Merced director of communications.

In 2001, the university said it would move the 2,000-acre core campus 2.5 miles away, to an existing golf course. “That reduced the potential impacts to wetlands on the Smith Trust lands and nearby by approximately 90 percent,” Grant said. With a $12 million grant from the David and Lucile Packard Foundation, the university will preserve 22,000 acres (about 34 square miles) of the Smith Trust property and others; of that, about 5,750 acres will be managed as a research reserve. An additional 20,000 acres may also be preserved under conservation easements, Grant said in mid-February. “We are very pleased that—with the support of the state, UC faculty and environmental groups such as The Nature Conservancy, the Audubon Society and the American Farmland Trust—we can confidently say that UC Merced is helping save vernal pools,” Grant said.

Nonetheless, some people remain very concerned about the impacts of the planned campus and adjacent community, and three environmental groups recently filed a lawsuit claiming the impacts have not been adequately evaluated. Certainly, the high-profile debate has done a great deal to raise Californians’ awareness of vernal pools and their vulnerable status.

This month, as the annual vernal-pool grand finale approaches, Michael Barbour again has his team of ecologists kneeling in brilliant patches of wildflowers. Asked about his view of the future, Barbour said he is cautiously optimistic, for two reasons.

“First, the number of knowledgeable spokespeople for vernal pools has finally come up to critical mass. They are no longer just amateur botanists, isolated academics, poets and landscape artists, and it’s no longer possible to disregard the pools. Second, vernal pools can co-exist with many of today’s land-use practices. They have continued to exist with native peoples, wild grazing animals, farmers, ranchers, moderate levels of domesticated livestock, and even urban neighborhoods. With reasonable care, they can be enjoyed next door to where most of us live.”

Sylvia Wright writes about the environmental sciences for the UC Davis News Service.