UC Merced

Vernal pools around Valley and UC Merced fill diverse role

They're not cow wallows, and they're certainly not seasonal mud holes.

That's what some people think vernal pools are. And they are wrong. Vernal pools are biologically diverse self-contained ecosystems unique to the Central Valley.

Vernal pools were also a large part of where the UC Merced campus wound up being built. The campus' original proposed site had to be moved to the southwest because 670 acres of pristine vernal pool habitat would have been destroyed.

Vernal pools still exist around the UC campus, and along the highways and in the foothills of Merced County. They are at their peak now, which is earlier than normal because of low rainfall and rising temperatures.

And those vernal pools are something to see. In the middle of grasslands, with waving fields of native grasses bending to the winds, a vernal pool is easy to spot. They are the areas full of yellow and white flowers, some with water still in the middle of the pools, some already dried up. Cattle like to graze near vernal pools and help keep the nonnative grass species from taking over the pools.

Vernal pools once covered nearly 22 million acres of California and Oregon. Up to 80 percent of those pools are now gone because of the growth of cities and some farming practices.

Lynn Hansen, a retired biology professor from Modesto Junior College, has spent a lot of time studying vernal pools and the species that inhabit the pools.

"They are seasonal pools, relying on rainfall and runoff," Hansen said. The pools don't have a year-round source of water, and the species that inhabit the pools have evolved to thrive in the impermanence of the pools.

The pools are home to invertebrates such as tadpoles and fairy shrimp. Those tiny critters are mere cysts in the dry ground when the winter rains come. Once the pools start to fill with water, the shrimp hatch, and then several generations live and die in the pools until the summer sun dries up the pools completely.

"All of the invertebrates come early in the season, when the water is still cool and at its deepest," Hansen explained.

What makes vernal pools unique is that unlike many areas on earth, vernal pools are found where there is either hardpan, a concrete-like clay that is found under the topsoil, or a rock base under the topsoil. The water that comes from rainfall or runoff is unable to soak into the ground, and vernal pools are the result.

Vernal means spring, and that's when the pools are at their most beautiful. Along with the invertebrates that live in the pools, many species of flowers have adapted to living alongside vernal pools, Hansen said.

"All of the flowers around vernal pools are keyed into the drying phases," Hansen said. Some of the most common flowers seen in the Merced area are white meadowfoam and yellow goldfields. These turn the hillsides into areas of gold and white, tucked among the green native grasses of spring.

Other flowers are also found around vernal pools, and they can be blue, purple, yellow and white. "It looks almost like a Joseph's coat," she said.

The vernal pools are important to wildlife, such as migratory birds, Hansen said. Because the pools teem with life in the spring, waterfowl like ducks use them as a place to feed. The pools are also home to tiger salamander and spadefoot toad larvae.

Zachary Simmons, a regulatory project manager for the United States Army Corps of Engineers, said vernal pools are unique to the Central Valley. Most of the species of animals and plants are only found near vernal pools.

"You will never see some of these flowers anywhere else in the world," Simmons said.

Along with invertebrates and plants, Simmons said there are also solitary bees that live and feed near vernal pools. Simmons said the bees live in the ground and use pollen from the flowers around vernal pools to feed their young.

"There are estimates that there are thousands of species of bees that are native to California, and we haven't identified all of them yet," Simmons said.

Both Simmons and Hansen said vernal pools are important because of their unique ecosystems, and the fact that they can be enjoyed by almost anyone.

"If we think of them as a park-like atmosphere, where you can enjoy something really beautiful, we realize how important they are," Hansen said.

Simmons said preserving the native species found around vernal pools is important for everyone.

"We don't understand the role the species play until they are completely gone," Simmons said. "Then we realize that maybe we should have kept those species around. When you get rid of a vernal pool, it's gone forever, and those flowers won't grow anywhere else. They're just gone."

And they can't be replaced by wallows and mud holes.

Reporter Carol Reiter can be reached at (209) 385-2486 or creiter@mercedsun-star.com.

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