MONTHLY NEWSLETTER

April 2025

Photo below shows the same viewpoint of the vernal pool during its predominant dry phase. (Photo credit: Scott McMillan)

Many species found in vernal pools are endemic; which means they are found in only one location on the planet. The amazing diversity of species that evolved within a single habitat resulted from the need for aquatic plants to survive through drought conditions while terrestrial plants needed to adapt to survival underwater. There is one threatened species and four endangered species found at the Poinsettia Preserve. They are shown below.

From left: Spreading navarretia (Navarretia fossalis), San Diego button-celery (Eryngium aristulatum var.parishii), California Orcutt grass (Orcuttia californica).

Photo credits: Scott McMillan

Vernal Pool Geology: Vernal pools form in shallow basin areas during winter rains and slowly dry out during the spring. They remain dry during the summer and fall. (Diagram credit: Scott McMillan)

The unique vernal pool habitat is generally associated with heavy clay soils that create an impermeable layer (claypan) that traps water on the surface and causes it to pool in shallow depressions.

Mima mounds are small, irregularly spaced hills that can form in-between small vernal pool depressions. The aerial photo below shows evidence of past vernal pools.

Aerial photograph taken in 1928 of the area now occupied by San Diego State University. The tiny dots are little round mounds (mima mounds), in-between which are depressions where the vernal pools form.

Same view in 2024. San Diego State University covers the exact location of the former cluster of vernal pools in the upper left-hand corner. The housing development consumed the vernal pools north of the canyon.

Photo credits CA Chaparral Institute

Seasonal Changes: Vernal Pools exhibit aquatic, flowering and drought phases. These phases are tied to our Mediterranean Climate with its annual pattern of flooding and drought. Organisms that live in the pools have evolved unique ways to survive and reproduce. During a single season pools may fill and dry several times; while in times of drought they may not fill at all.

Aquatic Phase: This phase begins with our winter rains as pools begin to form and generally lasts through late spring. The arrival of water allow organisms like the spadefoot toad above to come out of dormancy, plant seeds to germinate, or fairy shrimp eggs to hatch.

Below is flowering quill wort.

Flowering Phase: As the standing water begins to disappear in springtime, plants begin to bloom. Most plants are annuals and they tend to be small with lots of large flowers for maximum seed production. Many vernal pool plant species have seeds that can remain dormant for years, an adaptation that allows them to survive through periods of drought.

Otay Mesa mint below.

Drought Phase: Pool is dry to reveal claypan. Most plants have died and left their seeds behind. Some amphibians spend the drought underground in a dormant state; others move to terrestrial areas outside of the pool.

Photo credits: Scott McMillan

The Bigger Picture: Vernal Pools Play a Vital Part in California's Larger Ecosystem

Take the Coaster, Get off at Poinsettia Station and See the Vernal Pool Area for Yourself

The Carlsbad Poinsettia Station Coaster stop is a great place to view one of our remaining local vernal pool areas. In fact, why not visit and observe the pools throughout the seasons and watch for the phases.

If you park at the train station (or take the train and get off at Poinsettia Station), you can see the vernal pools best by standing on one of the 3 walkway bridges. The bridges traverse the vernal pool habitat before the train tracks. The linked map of the site shows the location of the informational signs about the pools. There are 3 signs at the Overlook Platform and one sign is located along the trail that begins on the south side of the parking lot.

"The greatest threat to our planet is the belief that someone else will save it." Robert Swan 

Preserve Calavera is offering to coordinate carpooling for north county folks who would like to attend. Contact us at info@preservecalavera.org

This was a long time coming but we can say goodbye to the notion of Cluster Housing once and for all in South Morro Hills. A motion to direct Oceanside city staff to remove all the references to Cluster Housing and bring back the South Morro Hills Community Plan (SMHCP) after the General Plan Update was approved on March 19. This is great news for Oceanside. 

Sequentially from top to bottom.

Berms and dirt jumps that were created at the site.

Volunteers hard at work to remove the jumps and berms and level off ground. Fencing was also repaired.

It is remarkable what a small group of dedicated volunteers can accomplish in a morning!

Hopefully the new signs will help potential trespassers to understand that this site is being restored.

A BIG THANK YOU TO THE 22 VOLUNTEERS FOR COMING OUT AND MAKING A DIFFERENCE!

and

A SPECIAL SHOUT OUT TO THE 13 VOLUNTEERS FROM RANCHO BUENA VISTA HS GENERATION GREEN ENVIRONMENTAL CLUB!

Although San Diego button celery is an endangered and endemic species, we are fortunate to have one of the largest populations at the our Poinsettia Station Vernal Pool Preserve. You can see how prolific it is in the photo at the beginning of the newsletter.

Flowering SD button celery. Photo credit Pacific SW Region USFWS.

Many of the plants that live in the vernal pool habitat are annuals; they die off yearly. San Diego Button Celery is a perennial herb (more info on annuals and perennials). It does die back during the drought phase but its living taproot remains in the dry clay waiting to sprout leaves when the rains arrive. Along with its taproot for survival, the plant produces seeds that can remain viable in the soil for many years under drought conditions. When the rains arrive and subsequent ponding, the seeds will germinate and the lifecycle will begin anew.

SD button celery (Eryngium aristulatum var. parishii) is a member Umbelliferae family, sometimes know as the Carrot, Celery or Parsley Family. In fact, button celery does have a carrot-like aroma and it forms stems and leaves that become stiff and prickly when it’s flowering and fruiting. This species is specially adapted for survival in wet conditions. There are specialized air channels in its roots that allow for gas exchange even though the plants are submerged in water.

Special thanks to Scott McMillan (Senior Habitat Restoration Ecologist/Botanist, Dudek) for sharing his knowledge and photos for this newsletter.