San Diego Natural History Museum--Your Nature ConnectionSDNHM Biodiversity Research Center of the Californias
BRCC
Binational Multidisciplinary Expeditions
Agua Verde-Punta
  Mechudo 2003

Isla Guadalupe 2000
Lindblad Binational 1997
On Collecting and
  Expeditions: A Botanical
  Perspective
Why are we exploring northern
Baja California Sur?

Natural History Expeditions to Northern Baja California Sur:
A Botanical Perspective

By Jon Rebman, Curator of Botany

Why do we go on natural history expeditions?
Why do we collect and make scientific specimens?
Why are we exploring northern Baja California Sur?
What is the next step after collecting?
What about future expeditions?

The Baja California peninsula is a narrow strip of land stretching for approximately 1300 km in length and ranging from 45 km to 240 km in width. Its geographic position, latitudinal span, and topographic heterogeneity have conferred a diverse assemblage of weather regimes including a Mediterranean-type, winter rainfall climate; extreme arid, hot desert conditions; and tropical, summer rainfall patterns. In addition, the peninsula's biogeographic history and physiognomy have resulted in a wide range of vegetation types which include coastal chaparral, conifer forest, low desert scrub, and tropical deciduous forest. This piece of land and its adjacent islands support a wealth of species diversity in many different plant families. It has been estimated by Wiggins in the "Flora of Baja California" that 2,958 total taxa and 686 endemic species can be found in Lower California, but recent plant discoveries and a more complete overview of the literature suggest that the flora probably consists of more than 4,000 taxa with a rate of endemism closer to 30%.

Many natural areas located in northwestern Mexico have had little scientific investigation. One such region is on the Lower California (Baja California) peninsula in the northern part of the state of Baja California Sur. Two mountain ranges, the Sierra San Francisco and the Sierra Guadalupe lie on the eastern edge of the Vizcaíno Desert and provide a link between the tropical components of the southern peninsula and temperate influences of the north. The small amount of scientific documentation that has been performed indicates that a sort of biological mosaic of species from both tropical and temperate climates exists in this area.

Sierra Giganta, photo by Jon Rebman

The topography and habitats of these mountain ranges are quite varied and provide refugia for species from both north and south. In the past, when sea levels were higher and the surrounding low deserts were under water, these mountain ranges probably provided the only corridor for plant and animal dispersal along the peninsula. The occurrence of some plant species in the area is still a mystery. The Catalina Cherry (Prunus ilicifolia ssp. lyonii; Rosaceae) was originally thought to be endemic to the California Channel Islands until it was discovered growing hundreds of miles south in the mountains of central Lower California. The Mexican Blue Oak (Quercus oblongifolia; Fagaceae) also occurs in the central peninsular mountains, but is disjunct from its main populations in northern Sonora and southeastern Arizona. There are many other unexpected plant distributions from the expedition sites that are helping scientists to understand biogeographical trends.

Adding to the appeal of the region, not only can many species' range extensions be found here, but many endemic species are present, and it is presumed that various new species may yet be discovered in this region.

The Sierra San Francisco and the Sierra Guadalupe are mountain ranges quite different in character. Neither area is well documented with scientific specimens, though the Sierra San Francisco is a popular destination due to its archaeological features. The Sierra Guadalupe has had almost no visits by biologists in its history.

The inaccessibility and remoteness of the northern Baja California Sur sites have contributed greatly to their lack of scientific investigation. However, with the modern development of more roads into each area, access is easier. Unfortunately, this same development also brings destruction associated with human influences. Therefore, expeditions need to be performed before an overall environmental degradation has been forced upon the region. The constant pressures of human impact such as agricultural and livestock farming, plus tourist development and activities, constantly loom overhead for this region.

Sierra de la Giganta. Photo by Jon Rebman.