Vernal Pools – Introduction

While there are many wetland areas on More Mesa, especially on both the eastern and western edges, the southeastern corner of More Mesa boasts our only documented vernal pool.  This special section is designed as an aid to understanding various aspects of vernal pools.  Specifically we will discuss:

  • What Are Vernal pools?
  • Life in Vernal Pools
  • Vernal Pools in California
  • Vernal Pools in Santa Barbara
  • Vernal Pool on More Mesa

What Are Vernal Pools?
Vernal pools are a particular kind of ecosystem.  They form as a result of a distinctive climate, topography, and soil, and are distinguished by the organisms within them.  The climate must have mild winter temperatures and a summer drought; namely, a “Mediterranean climate” such as is found in Southern California.  The vernal pool must be a shallow depression that will catch water from winter rains.  In addition, it also must have soil with an impermeable layer, such as clay, to insure that the water will remain in the pool for several months of flooding during the winter-wet season. In brief, a vernal pool is a specific ecosystem having organisms restricted to special habitats that flood temporarily in the winter and early spring, but are dry the remainder of the year.

Life in the Vernal Pool
The organisms of vernal pools are the ultimate indicator of the vernal pool habitat.  An annual cycle of flooding and drying creates an environment where few species can survive.   Indeed, the physical conditions in a vernal pool provide a particular habitat for some plant and animal species that can survive nowhere else.  During the course of a year, there are four environments in the vernal pool:

  • Late Autumn: When first rains fall, the soil is saturated and seeds begin to germinate
  • Height of Winter Rains:  Pool fills to the maximum, pool animals flourish — aquatic insects, zooplankton, ducks, frogs, water birds
  • Late Winter and Spring: Water levels recede, plants mature to full flower — thus the name “vernal” for the pool
  • Late Spring to Early Autumn: Extended drought and little life is apparent

vernal flowers
Vernal flowers blooming around a drying vernal pool,
Camino Corto Open Space, May 01, 2011.