California Vernal Pools: An Introduction

California Vernal Pools

An Introduction

California's vernal pools are a beautiful local ecosystem. Formed when runoff and precipitation fill up land depressions over impermeable rock, they are located largely in Central California but can also be found all across the Golden State. 

(from http://www.cnps.org/cnps/publications/fremontia/january_2000/3vendlinski.pdf)

The name vernal comes from the Latin word meaning spring, and the vernal pools are named the time during which their pools are the deepest and filled with the most water. Vernal pools experience their highest precipitation during spring. However, during the dry summer months, the water is evaporated from the pools and they are left mostly barren and dry. Often rings of flowers form around the pools, lending to an otherworldly appearance like a fairy ring: species like the San Diego mesa mint (Pogogyne abramsii), which looks like a rich purple fog.

The California vernal pools are home to many organisms that thrive and survive in its strange and somewhat harsh climate changes and variations. One such organism is the fairy shrimp, which must live in a vernal pool or similar wetland (obligate species). Some species--such as amphibians--use the pools only when they are filled with water, and spend most of their lives in the surrounding uplands. Many plants and animals spend the dry months as eggs or seeds, and grow and reproduce during the wet season. Also, birds such as hawks, egrets, and ducks use them for seasonal water and food supplies or stops as they migrate. The spreading of seeds by migrating birds is crucial for moving different species from place to place.

FUN FACT: HALF of all species found in vernal pools are endemic to California.

Vernal pools come in all sizes: they can be as small as only a few inches across or as big as small lakes. Some are found in complexes, when many occur near each other. They sometimes share drainages, which are called vernal swales. However, due to the different patterns of rainfall year by year, pools close to one another can support entirely different groups of animals and plants. In years of extremely heavy rainfall, though, some pools close to each other can coalesce. 

Sources:

http://www.cnps.org/cnps/publications/fremontia/january_2000/3vendlinski.pdf)

http://www.dfg.ca.gov/biogeodata/wetlands/pdfs/VernalPoolAssessmentPreliminaryReport.pdf

http://water.epa.gov/type/wetlands/vernal.cfm

http://www.osti.gov/energycitations/basicsearch.jsp