Vernal Pools

June 15, 2023

Question: How were California’s vernal pools impacted by this year’s winter storms?

Answer: Vernal pools are a type of temporary wetland that support many native animal and plant species ( https://wildlife.ca.gov/Conservation/Plants/Vernal-Pools ) in our state including the California tiger salamander, vernal pool fairy shrimp and annual plants such as goldfields, downingia and succulent owl's clover. Vernal pools are found in locations throughout the state including the San Francisco Bay Area, Central Valley and coastal terraces in Southern California. An important quality of vernal pools is their hard underground layer which prevents water from draining downward into subsoils. Because of this underground layer, vernal pools are typically filled with water during the rainy season. In springtime, water gradually evaporates until pools become dry in summer and fall. Colorful displays of vernal pool wildflowers are often visible in spring as pools dry. Native species have adapted to this unique annual cycle of inundation, gradual evaporation and dryness.

Large storm events, like this year’s series of atmospheric rivers, typically fill pools to their maximum level which causes excess water to spill into adjacent areas. The resulting assemblage of plants can vary from year to year depending on when and for how long the vernal pools were filled with water. No two years are the same. Some vernal pool plant species may do well during wet seasons, and some may do better in years that are less wet. Many annual plants have seeds that can remain dormant for years, which is an adaptation that allows them to survive extended drought periods and flourish in wet years like this one. Additionally, increased precipitation can boost food resources and improve breeding and rearing habitat for wildlife.

We have a State vernal pool refuge behind our house. This is a pretty accurate description of what happens