By Matt Guilliams

In the not so distant past, when the footprint of humans was less heavy on the landscape, the marine terraces, mesas, and valley bottoms of parts of the Californias (Baja California, Mexico and California, USA) would have looked quite different than they do today. In these areas where urban and agricultural landscapes now dominate, vast swathes of flat to gently undulating terrain would have been the natural condition. 

These landscapes would have been blanketed with a rich cover of shrubs, wildflowers, and grasses. When certain soil conditions were present, water from mild winter rains would gather in the numerous low lying areas, yielding a vast, shimmering constellation of short-lived winter pools. Over time, an endemic flora and fauna evolved in these temporary ponds, contributing to a distinctive ecosystem called a vernal pool.

What makes a vernal pool?

Vernal pools are rare and endangered wetland ecosystems that occur in all five Mediterranean-type climates of the world (Keeley & Zedler, 1998). These marvelous ecosystems occur in shallow depressions that fill with water during the cool winter months, when they are essential habitat for gracefully swimming fairy shrimp, amphibians, and scores of migratory bird species. 

As the water evaporates in spring, the once dominant aquatic biota yields to a dazzling and multi-hued procession of annual wildflowers, many of which occur in the vernal pools of the Californias and nowhere else on earth. Upon the arrival of hot summer temperatures, vernal pools dry completely and their rich host of plants and animals retreats underground to await the next winter rains. Exquisitely adapted to our Mediterranean-type climate, vernal pools and the plants and animals they support are truly among our most precious natural resources.

Our heritage at risk

The vernal pools of the Californias harbor tremendous endemic plant and animal diversity, yet despite their critical biological importance, a large percentage of vernal pools have been destroyed (e.g., see Holland, 2011). 

Our team of Baja California vernal pool researchers has calculated that 96% of vernal pool landscapes have been lost in Baja California (Guilliams et al. in review). This estimate is among the highest reported for vernal pool loss in western North America, with only San Diego County, California having a greater percent loss (96-98%; Bauder & McMillan, 1998). 

The rapid pace of loss in northwestern Baja California has inspired the formation of a bi-national team of biologists and conservationists to learn more about the remaining pools so that they can be better understood and protected. 

Research and advocacy focusing on Baja California vernal pools

The vernal pool landscapes of Baja California require urgent intervention to protect those pools that remain. In partnership with Terra Peninsular and Sociedad de Plantas Nativas de Baja California, our vernal pool team has been active in research and conservation in northwestern Baja California since 2010. 

With a team of nearly 20 biologists, our efforts have been collaborative and multi-faceted. Our initial efforts were geared toward understanding present day and historical distributions of vernal pools in Baja California. The results of this study, presently in review, include a systematic report of the distribution of vernal pools in Baja California and the first assessment of vernal pool loss in the region. This work sets an important baseline for biologists, conservationists, and land managers, allowing prioritization of future conservation and research efforts. 

Beyond mapping of vernal pools, we are documenting and studying the plants and animals that live within them. Although Baja California vernal pools are somewhat less diverse than pools to the north, there are a number of fascinating vernal pool plants that occur predominantly or wholly in northwestern Baja California and nowhere else; some Baja California vernal pool plants occur just north of the international border and are often considered rare in the USA, e.g., San Diego button celery (Eryngium aristulatum var. parishii; Apiaceae), California Orcutt grass (Orcuttia californica, Poaceae), and spreading navarretia (Navarretia fossalis; Polemoniaceae). 

The Baja California populations of these species are often more numerous than those in the USA, and thus the protection of Baja California vernal pools will contribute importantly toward the long-term persistence of these plants in the wild.

At least four species of plants are endemic to Baja California vernal pools, and three of these are new to science. The Valle de Las Palmas region supports a highly localized mesa mint (Pogogyne sp. nov. “mexicana”; Lamiaceae) related to but distinct from relatives in the San Diego area. The entire distribution of this yet-to-be-described plant is two small river terraces in single, rapidly developing valley. The Colonet region to the south supports two narrow endemics, Centromadia perennis (Asteraceae), and one yet-to-be-described popcorn flower (Plagiobothrys sp. nov. “colonetensis”; Boraginaceae). Finally, the San Quintín region is the home of an undescribed button celery (Eryngium sp. nov., Apiaceae), which -until our team discovered two new populations earlier in 2016- was thought to have been driven to extinction before it could be formally described.

Our team has also initiated region-wide genetic studies of the endemic fairy shrimp of Baja California (Branchinecta; Crustacea), with a focus on regional endemic, B. sandiegonensis. This work, led by Dr. María Clara Arteaga Uribe and her graduate student Nayeli Escudero Castelán at Centro de Investigación Cientifica y de Educación Superior de Ensenada (CICESE), has revealed interesting genetic patterns between coastal and inland vernal pool regions in northwestern Baja California. In particular, fairy shrimp from the Valle de Las Palmas area appear to be genetically distinct from fairy shrimp from coastal locations (Escudero-Castelán et al., 2014). This pattern is similar to that of the undescribed mesa mint species, with isolated, interior populations in Valle de Las Palmas appearing distinct from close relatives in coastal San Diego County. 

What’s next?

Although much has been accomplished in recent years, we still know relatively little about Baja California’s vernal pools. Therefore, it is imperative that we continue to study and attempt to protect the remaining vernal pool landscapes. In the coming field seasons, biologists will continue to study the floristics of the Baja California vernal pools and will work toward formally recognizing the three undescribed vernal pool plant species. 

About the author

Matt is a botanist at the Santa Barbara Botanic Garden, where he holds the Ken and Shirley Tucker Plant Systematist endowed chair and is the Curator of the Clifton F. Smith Herbarium. 

His research focuses on themes in plant evolutionary biology, including the inference of evolutionary relationships using morphological and molecular data, biogeographic inference, and study of adaptive radiation in the California Floristic Province. In Baja California, Matt has been active as the leader of a long-term project focusing on the study and conservation of vernal pool ecosystems in the region.

Matt completed a bachelor’s degree in Biology at San Diego State University, worked for various private and public organizations as a botanist, and then completed a master’s degree in Evolutionary Biology (also at SDSU). Matt completed his dissertation at the University of California Berkeley in 2015.

References

• Bauder, E. T., & McMillan, S. (1998). Current distribution and historical extent of vernal pools in southern California and northern Baja California, Mexico. Pages 56-70 in Witham, C. W., Bauder, E. T., Delk, D., Ferren, W. R. J., & Ornduff, R. (Eds.) (1998).  Ecology, conservation, and management of vernal pool ecosystems, proceedings from a 1996 conference. California Native Plant Society, Sacramento, CA.
• Escudero-Castelán, N., Arteaga, M. C., & Guilliams, C. M. (2014). Diversidad de anostracos de las pozas vernales en el Norte de Baja California. First Annual International Symposium of Environmental Biology, CICESE. Ensenada, B.C., Mexico.
• Guilliams, C. M., Hasenstab-Lehman, K., Delgadillo Rodríguez, J., & Baldwin, B. G. in review. Vernal pool landscapes of Baja California, México: an ongoing project to assess vernal pool loss and protect what remains. 
• Holland, R. F. (2011). Great Valley vernal pool distribution rephotorevised 2005 in Alexander, D. G, & Schlising, R. A. (Eds.) Research and Recovery in Vernal Pool Landscapes. Studies from the Herbarium, Number 16, California State University, Chico, CA.
• Keeley, J. & Zedler, P.H. (1998). Global distribution of vernal pools in Witham, C. W., Bauder, E. T., Belk, D., Ferren, W. R. Jr., & Ornduff, R. (Eds.). Ecology, Conservation, and Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference. California Native Plant Society, Sacramento, CA.