"Oh, no," I thought, as I pulled into the parking area at The Nature Conservancy's Jepson Prairie. Preserve. "This is a vernal pool?" Throughout the drive from Berkeley to California's Central Valley I'd been repeating the musical words: "vernal pool, vernal pool, vernal pool." Though I'd never seen one, the name evoked something small and green, nestled in a mossy hollow, far from the madding crowd. But in the parking area, reality intruded. Olcott Lake, the biggest of the pools on the 1,600-acre preserve, looked more like a huge puddle of milky coffee than an emerald jewel. On this wet spring day it measured a quarter-mile wide by a half-mile long, and maybe two feet deep. And the madding crowd was uncomfortably close: big-bellied C-141s took off from and landed at a nearby air force base, and a stream of 18-wheelers roared down an adjacent road. I could barely suppress the heretical thought that Jepson Preserve was just-well-some puddles in a pasture. Later, when I confessed my reaction to Oren Pollak, a Nature Conservancy biologist, he chuckled indulgently. "You have to get up close to the pools to understand them," he said. "But I guarantee that to know this place is to love it."
As I was soon to discover, there is a lot about these pools to know. They are fragments of an ancient, oncewidespread landscape; and though they now comprise only a tiny sliver of the state's acreage, the pools are home to 69 plant species that occur only in California. Several of these plants are on the federal endangered species list. The animals are unique as well: the fairy shrimp, Delta green ground beetle, and California tiger salamander are all both endemic and endangered. Yet a lot about the pools remains unknown. For instance, how were the gentle ups and downs of the vernal pool landscape created? Competing theories abound: Maybe eons of burrowing by gophers and moles formed the low mounds; maybe the underlying clays absorbed water, causing the ground to heave and buckle; maybe the wind scoured the hollows down to the impermeable hardpan below. Regardless of how the basins formed, every year for millennia the rains that begin in November collect in these shallow depressions, and the underlying clay soil keeps the moisture from seeping away. Throughout the winter the pools are brim full, but as the rains slacken in the spring they begin to shrink. By July, the only trace of the Jepson pools will be some spots of bare, cracked clay, like the ghostly smiles of a thousand Cheshire cats. But the pools' tenants are a resourceful bunch. The annual deconstruction of their habitat has acted as an evolutionary crucible, forcing them into ingenious adaptations. Some thrive in the aquatic phase and endure the arid; others hang on through the wet months but flourish when the temperature rises and the ground dries out. Everyone who studies pools has a favorite example of this adaptability. Larry Serpa, the Conservancy biologist who showed me around Olcott, collected a crustacean menagerie with one swoop of his funnel-shaped net, but he admits to a special fondness for the tiny, transparent Branchinecta conservatio, or Conservancy fairy shrimp. The shrimp lay their eggs during the aquatic phase, then die en masse as the pool evaporates, Serpa explained. The eggs fall into the cracks in the hardpan or among the dried grasses that ring the empty pool. By the time the next generation appears in the fall, most of the predatory insects will have disappeared, leaving the tiny hatchlings to grow in relative peace. Branchinecta has matched its life cycle to that of the pool; a less demanding environment would do it in. Plant ecologist Paul Zedler, on the other hand, particularly admires an amphibious plant called Pogogyne zizyphoroides. Unlike the fairy shrimp, Pogogyne tolerates the wet of winter so it can bask in the heat of summer. In March only a few of its leaves float on the surface, but during a pool's annual cycle the plant changes dramatically. The round leaves fold in on themselves, and the slender stem branches as the water level drops. Pogogyne spreads, flowers and fruits on the cracked clay basin; byJuly, it shows no trace of its aquatic interlude. But all this adaptability may not save Branchinecta, Pogogyne and their neighbors, because what they can't adapt to is us. Development is the biggest threat: relatively flat, well-watered land is an increasingly precious commodity in the Golden State. And since powerful machines can now break up the hardpan and drain the soil, it seems that everybody-farmers, real estate developers, highway builders-wants a piece of the vemal pool landscape. "The bad news," says the Conservancy's Pollak, "is that we've lost all but between 5 and 2 percent of California's pools, maybe more. The good news is that we might be able to save most of the rest." In the early eighties, The Nature Conservancy recognized the threat to pools and their surrounding grasslands. Between 1980 and 1983, the Conservancy acquired five major vernal pool sites, starting with Jepson Prairie. The move toward preservation is building: the Army Corps of Engineers recently recognized vemal pools as wetlands. As a result, anyone who builds on vemal pool land must either buy and preserve an existing vernal pool elsewhere or recreate the pool that was displaced. Pool experts welcome this step, but wonder whether it's possible to build a living vernal pool. The few artificial pools that do exist are five years old at most. "That's much too soon to tell if they're going to work" long-term, says Tom Griggs, a Conservancy ecologist who works on vernal pools. "Besides, none of them have anything like the species diversity of real pools."
I went back to Jepson Prairie several weeks after my first visit, this time as an initiate into its mysteries. The big pool was lower and some smaller pools had already vanished; the drydown phase of the cycle had begun. This time I knew that the Conservancy fairy shrimp had laid their eggs and died, and that a new generation would emerge after a long, hot sojourn on the hardpan and a short soak in the rain. This time I knew that Pogogyne was just gathering the strength to reinvent itself as a tough, stringy summer survivor. This time I knew that vemal pools like Olcott had dappled the Central Valley for millennia. I remembered what Paul Zedler said: "The main reason we should preserve these pools is that they give us a sense of place; they're part of a landscape that used to be. In a way, these pools define what it is to be in Califomia in the spring."
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