Biogeographic Regionalization of the Mexican Transition Zone

Abstract

The Mexican Transition Zone is the area where the Neotropical and Nearctic regions overlap. In its strict sense followed in this book, it corresponds to the moderate- to high-elevation highlands of Mexico, Guatemala, Honduras, El Salvador, and Nicaragua. This area is considered a transition zone between the Nearctic and Neotropical regions, so from the perspective of biogeographic regionalization, it should be assigned simultaneously to both regions. Within the Mexican Transition Zone, I recognize 5 biogeographic provinces and 22 districts. The Sierra Madre Occidental province is situated in western Mexico at elevations between 200 and 3000 m, with most of the area above 2000 m; it includes the Apachian and Durangoan districts. The Sierra Madre Oriental province is situated in eastern Mexico at elevations above 1500 m; it includes two subprovinces: Austral-Oriental (with the Saltillo-Parras and Potosi districts) and Hidalgoan (with the Sierra Gorda and Zacualtipan districts). The Transmexican Volcanic Belt province is situated in central Mexico, at elevations above 1800 m; it includes two subprovinces: West (with the Otomi and Tarascan districts) and East (with the Aztec and Orizaba-Zempoaltepec districts). The Sierra Madre del Sur province comprises south central Mexico at elevations above 1000 m; it includes three subprovinces: Western Sierra Madre del Sur (with the Jaliscian and Jaliscian-Manantlan districts), Central Sierra Madre del Sur subprovince (Michoacan district), and Eastern Sierra Madre del Sur (with the Guerreran and Oaxacan Highlands districts). The Chiapas Highlands province comprises southern Mexico, Guatemala, Honduras, El Salvador, and Nicaragua, basically corresponding to the Sierra Madre de Chiapas, from 500 to 2000 m altitude; it includes the Sierra Madrean, Comitanian, Lacandonian, Soconusco, Guatemalan Highland, and Nicaraguan Montane districts.