Biogeographic regions and β‐diversity of woody dryland legumes in the Baja California peninsula

We analysed the floristic turnover, or β‐diversity patterns, of woody legumes in Baja California, the 1300 km long peninsula in NW Mexico. From the specimen labels of nine herbaria, we digitized 4205 records from 78 species and projected them onto a grid of 205 cartographic cells (20’ longitude × 15’ latitude). We found that the E‐W turnover from the Pacific coast to the Sea of Cortés was high (ca. 60% change from one cell to the next) and that it was significantly associated with topographic variation across the peninsula. An analysis of between‐site similarities showed that floristic regions in the peninsula have well defined boundaries, and that floristic similarities tend to extend for long distances along the coastal corridor of the Sea of Cortés. Finally, a numerical classification of Baja California based on the floristic attributes of the cells separated the peninsula into five well defined regions that coincide very closely with regionalizations, previously proposed by various authors using descriptive methods, and with the areas of endemism described for the peninsula in a previous paper. We conclude that the ecological regions of woody legumes in the peninsula clearly reflect the two main environmental forces that act on it, namely, the 1300 km long temperate–tropical climatic gradient and the dramatic E–W gradient running from the Pacific Ocean ca. 100 km across the mountain range into the Sea of Cortés.