Bioclimatic belts of Sierra Madre Occidental (Mexico):A preliminary approach

A bioclimatic synthesis of the Sierra Madre Occidental (SMO) based on the diagnosis of data from 159 meteorological stations, the floral and vegetation data collected in field surveys, and in the bibliographic revision. The considered area is above the altitude of 1800 m included in the physiographical province of SMO, which entirely belongs to Tropical macrobioclimate, being represented by the bioclimates Tropical Pluviseasonal and Tropical Xeric. Broadly speaking, the first is distributed in the highlands and on the western slope of the range, while the second is sited in the dry mountain ravines and on the eastern slope. Fourteen isobioclimates were recognised, 5 for the bioclimate Tropical Xeric (Thermotropical Dry, Mesotropical Semiarid, Mesotropical Dry, Supratropical Semiarid and Supratropical Dry) and 9 for the Tropical Pluviseasonal (Thermotropical Subhumid Mesotropical Subhumid, Mesotropical Humid, Supratropical Subhumid, Supratropical Humid, Supratropical Hyperhumid, Orotropical Subhumid, Orotropical Humid and Orotropical Hyperhumid). Each one has its corresponding vegetation belt, with emphasis in the structure of its potential natural vegetation, its main bioindicators and its catenal distribution. These results are complemented by distribution maps of the bioclimates, thermotypes and ombrotypes present, and by three vegetation transects recognised along both routes made at different latitudes.