Vernal Pools Enable Biodiversity

Vernal Pool Network

Vernal pools enable biodiversity.

More than 90% of California’s vernal pools have already been lost. Great efforts are being made to protect the remaining vernal pools, as their disappearance marks the loss of rare and important habitat and some of the associated plant and animal species as well.

In Placer County thousands of acres of functional vernal pools lie within the footprints of various proposed developments. Tenuously protected by state and federal environmental regulations, their future remains at stake.

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Splash Vernal Pool Field Trip

Vernal pools derive their name from the Latin vernus which refers to spring. Perhaps this was the season when they were first noticed and described – their showy wildflower displays dotting lush green grasslands. Vernal pools are actually intermittent bodies of water; wet during a portion of the year but bone-dry during the balance of the year. Their sizes vary from only a meter or two in diameter to large vernal lakes of sizeable acreages. Regardless of their size they all hold in common a drastic and characteristic wet and dry, or “boom and bust” ecological economy.

One of the “signature” landscapes of Placer County are vernal pools. Vernal pools are shallow depressional wetlands, formed when the percolation of rainwater and surface run-off is impeded by the presence of a restrictive, subsurface layer. These pools remain inundated throughout late winter and early spring, evaporating slowly as temperatures rise and precipitation diminishes. Vernal pools can range anywhere in size between 30 square feet to the size of a small lake.

Although most vernal pool critters are very small, they are an important food source for shore birds and waterfowl. Other birds, like the Great Blue Heron (Ardea herodias), feed on amphibians that are attracted to the pools for breeding; geese eat vegetation that grows around the pools.

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Meet Some Vernal Pool Microscope Critters!

While other freshwater wetlands are dominated by aquatic insects, the vernal pool is a veritable showroom for their saltwater counterpart – the crustaceans. Related to crabs, shrimp, and lobsters, vernal pool crustaceans are important zooplankton and swimming arthropods that emerge from eggs and cysts dormant in the dried mud from the previous year. Copepods, seed shrimp, clam shrimp, fairy shrimp and “monster” tadpole shrimp occupy various niches during the pool’s ecological development, and each has its own incredible survival story. Habitat loss and conversion has threatened the future of numerous vernal pool crustaceans – enough to warrant the placement of various fairy shrimp and the tadpole shrimp on state and federal Endangered Species Lists.

Recent hydrological studies show that vernal pools do not simply fill from direct
precipitation nor do they empty solely by evapo-transpiration. Instead, lateral subsurface flow imparts a high degree of connectivity among pools. Effective conservation requires the establishment of a network of many
reserves distributed throughout all vernal pool regions
, assuring the inclusion of all plant community diversity.

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