Forrest Shreve revisited: The ecological regions of Baja California and the Sonoran Desert under large-scale environmental change

Background/Question/Methods

The complex geological and biological history of the Baja California peninsula, combined with its geographical location in the tropical-temperate transition, produces a striking and unique replication of the larger-scale temperate-desert-tropical transition in the North American mainland. This sort of “small-scale continent,” has fascinated scholars for almost two centuries. As a result, researchers have proposed several biological regionalizations for Baja California since the early 1900s, under different methodologies and with different perspectives. At same time, during this period the peninsula has experienced an increasing utilization of their natural resources by human activities, affecting their ecological patterns and processes at different geographical scales.

Our principal objective was to identify and analyze the main discrepancies among different approaches, and propose a new synthetic ecoregional map. Secondly, we explored how ecological change derived from anthropization is affecting different ecoregions.  

To achieve this we did an exhaustive review of the published literature on the natural geography of Baja California. Based on this review we synthesized the main driving ideas behind the views of these naturalists and scientists, and found that most biogeographical studies of the peninsula agreed on a general framework defined by three main peninsular biomes: northwestern Mediterranean scrubs, southern tropical scrubs and the desert region lying in between, articulated by three axes of climatic variation—long latitudinal span, strong east-west contrasts in climate, and pronounced topography. This common biogeographical outline was delineated by Edward Nelson in 1921 and culminated by Forrest Shreve thirty years later.

Results/Conclusions

We identified seven major points of controversy in the different approaches of the peninsular biogeography and summarized the discrepancy zones, which were analyzed at a workshop of regional experts. Together we generated a new synthetic proposal of 14 ecoregions.

Finally, we generated the human footprint of the peninsula based on the distribution of localities, agriculture and vial infrastructure and found that the higher affectation occurs in the coastal ecoregions of the northern Mediterranean and southern tropical regions.