The research team, led by scientists working within the framework of the Worldwide Bioclimatic Classification System developed by Salvador Rivas-Martínez, set out to resolve a persistent problem. Previous efforts to classify and name Mexican vegetation types, stretching back to the late nineteenth century, produced valuable but inconsistent results because they lacked shared criteria and joint input from both geographical and botanical perspectives. By combining climatic data with advanced geographic information system techniques, the researchers hoped to unravel the complex interactions between climate and vegetation and to provide a sound, unified system for identifying the country’s bioclimatic physiognomic patterns.

Bioclimatology, the discipline at the heart of the study, examines the relationship between long-term weather patterns and the responses of living organisms. Its intellectual roots reach back to pioneers such as Alexander von Humboldt and Carl Troll, who explored the links between climate and vegetation, and it matured as an independent field during the twentieth century as data collection improved and awareness of climate change grew. The Rivas-Martínez system used in this research is built on the close interrelationship between climate, vegetation and geography. It treats seasonality of precipitation, temperature and continentality, the difference between the warmest and coldest months, as the key variables that determine which bioclimates exist within broader macrobioclimates, and it establishes a predictive, hierarchical typology that nuances vegetation responses within the same macrobioclimate.

To build the bioclimatic side of the map, the team drew on the Digital Climatic Atlas of Mexico, which compiles monthly and annual averages of precipitation and temperature from 1902 to 2011 as recorded by the National Meteorological System. From these data they calculated a suite of bioclimatic parameters and indices, including the thermicity index, which weighs the intensity of cold as a limiting factor for plant communities, the compensated thermicity index, which corrects for excess cold or temperance in continental or hyperoceanic territories, and the annual ombrothermic index, the ratio of positive precipitation to positive temperature, which determines the ombrotype. The ombrothermic index of the driest bimonth captured the severity of seasonal drought, a decisive factor in a country where water availability varies dramatically from region to region.

The vegetation side of the analysis came from the National Institute of Statistics and Geography of Mexico, whose land cover data at a scale of 1:250,000 were regrouped according to the Standardized Hierarchical Vegetation Classification. The researchers reclassified the vector layers into three physiognomic categories: forests dominated by woody-stemmed plants over five metres tall, shrublands dominated by plants with woody or succulent stems mostly under five metres, and herbaceous and non-vascular formations dominated by plants without a woody base. Water bodies and cultural land cover types were also depicted. Working at a final scale of 1:4,000,000, polygons smaller than 256 square kilometres were merged with adjacent larger polygons, a pragmatic decision that simplified the mosaic while preserving the dominant patterns.

The map crossing procedure, performed in ArcMap GIS 10.5, revealed five ombrotypes and five thermotypes as the major bioclimatic classes of Mexico. The ombrotypes range from (Hyper)Arid through (Semi)Arid, Subhumid and Humid to Hyper-Ultra Humid, while the thermotypes span Infra, Thermo, Meso, Supra and Oro tropical temperature classes. Arid conditions dominate the national picture, covering 55.6 percent of the surface, with Subhumid and Humid zones together accounting for roughly 43 percent. Combining these classes yielded 13 distinct bioclimatic belts, the most widespread being the (Semi)Arid Mesotropical, which alone covers 33.5 percent of the country. The (Semi)Arid and Subhumid Thermotropical belts follow at 14.8 and 13.2 percent respectively.

Crossing these bioclimatic belts with the physiognomic data allowed the team to recognise 17 native vegetation types: 11 forests, 3 shrublands and 3 herbaceous formations. The forests tell a story of climatic gradients. Spiny deciduous woodlands locally known as Mezquital and Deciduous Dry Forests occupy more than 156,000 square kilometres of arid and dry Infra-Thermo-Meso-Supratropical terrain. Subhumid to Humid Thermotropical and Mesotropical forests, covering some 328,000 square kilometres, comprise Subdeciduous broad-leaved forests and needle-leaved conifer forests respectively. Supratropical forests cling to mountainous landscapes, marking transitions toward the Mexican timber line, while the rare Orotropical Hyper-Ultra humid belt supports evergreen perennial broad-leaved forest.

Shrublands emerge as the quiet giant of the map, covering 532,521 square kilometres and representing climates under water stress for long stretches of the year. This category encompasses the astonishing xerophytic shrublands of the Mexican deserts, including Cardonal dominated by the giant cactus Pachycereus pringlei, Tetetzal built on Neobuxbaumia tetetzo, Izotal with Yucca periculosa, Nopaleras of Opuntia cacti, and Magueyal of Agave species. A substantial portion, 158,117 square kilometres, corresponds to the Mediterranean macrobioclimate, supporting Chaparral shrublands dominated by genera such as Adenostoma, Arctostaphylos, Ceanothus and Quercus, found in Baja California and extending into Chihuahua. Herbaceous and non-vascular formations, meanwhile, spread across more than 165,000 square kilometres of arid to subhumid belts.

Perhaps the most sobering figure in the study concerns human influence. Cultural areas, reflecting agriculture, urbanisation and land-use change, now cover 529,794 square kilometres, or 27.3 percent of the national territory, and they predominate in the (Semi)Dry Meso-Supratropical regions. Because small patches of cropland were merged into neighbouring vegetation polygons during cartographic simplification, the authors warn that the true cultural footprint is underestimated, and they estimate that up to 51 percent of the country could ultimately be converted to cultural land cover. Water bodies, critical for aquatic biodiversity, account for a comparatively modest 12,958 square kilometres.

The implications reach well beyond cartography. Vegetation patterns serve as indicators of climate change impacts, guiding predictions and strategies for mitigation and adaptation, and they underpin ecosystem services from water purification and pollination to climate regulation. The authors note that regions experiencing arid conditions may face mounting challenges related to water scarcity and desertification, while shifts from Humid toward Subhumid ombrotypes have already been projected for Mexico. By providing a spatially explicit, climate-linked baseline of the country’s native vegetation, the new map offers conservation planners, land managers and policymakers a tool for identifying biodiversity hotspots, targeting restoration, and anticipating where climatic change will press hardest on ecosystems. The team acknowledges that finer-scale floristic data and soil information remain to be integrated, but the core message stands: harmonising bioclimatic and geobotanical methodologies is essential if megadiverse nations are to understand, and defend, the living landscapes that climate and history have given them.

Subject of Research: Bioclimatic and vegetation mapping of Mexico's plant formations

Article Title: A coupled cartographic approach between bioclimatology and vegetation formations of Mexico

Article References: Gopar-Merino, F., Velazquez, A., González-Pérez, A., del Río, S., Mas, J. F., & Penas, Á. (2024). A coupled cartographic approach between bioclimatology and vegetation formations of Mexico. Vegetation Classification and Survey, 5, 153-164. https://doi.org/10.3897/vcs.120442

Image Credits: AI Generated

DOI: 10.3897/VCS.120442

Keywords: bioclimatology, vegetation classification, Mexico, mapping, biodiversity, ombrotypes, thermotypes, shrublands, forests, GIS, conservation, climate change