California Vernal Pools

A vernal pool is actually a seasonally flooded area that looks like a small depression in the landscape during the dry periods. It’s actually a very important ecological resource, but can easily be overlooked. During the wet season, which is the winter time in California, the depression fills with water and provides important habitat for migrating birds, insects, crustaceans like the fairy shrimp, small invertebrates and amphibians like frogs. It’s interesting that the eggs of the fairy shrimp, five species of which are threatened or endangered, can live in the soil of a dry vernal pool for several years and hatch in a little over a day once water fills the pool. Because of the importance of vernal pools, regulating agencies like the US Army Corps of Engineers require biological surveys to be conducted prior to any development in areas where vernal pools might be found.

There is archaeological evidence that vernal pools were used by the Native Americans prior to European settlement. Stone tools have been found around existing vernal pools that indicate that seeds and roots were gathered and used as a food source in the spring time. The Native Americans aren’t the only ones to use the pools. Animals have used them for thousands of years as watering holes, and even modern cattle frequent them and providing the area isn’t over grazed, it may actually be beneficial to have the cattle spreading native seeds around the pool.

Vernal pools are usually found in areas that used to contain waterways where alluvial deposits were exposed once the water dried up or retreated. These areas are slightly lower in elevation than the surrounding landscape, so they fill with water once the water table rises. Within days the vernal pool springs to life with a vast colorful array of flowers that attract bees, butterflies, birds and a host of other insects and animals. Some, like the fairy shrimp, rely on the pools for their survival and if the pools are destroyed by development or off highway vehicles, the habitat and ecosystem can suffer. Many vernal pools have been identified by the various wildlife and regulatory agencies, but biological surveys are still required before any projects can be approved in the area. Only qualified biologists who are familiar with vernal pools and the indicators that could lead to a vernal pool are permitted to survey. While some developers might consider the regulatory process inconvenient, it is necessary to preserve this important habitat.