Diversidad florística en cimas de la Sierra Madre Occidental, México, y su relación con variables ambientales

The highest peaks of the Sierra Madre Occidental harbor plant communities with some alpine vegetation features. These sites are ecologically important because, in addition to their high levels of diversity, they are among the first land areas where effects of climatic change can be detected. The objectives of this work were to provide information about plant cover and floristic composition on the summit of three of the highest peaks of the Sierra Madre Occidental: Cerro Gordo, Huehuento and Las Antenas, as well as to compare their species richness, to measure their floristic similarity, and to identify the main environmental variables that may have an influence on vegetation. Sampling was based on the methodology proposed by the GLORIA Project and data were analyzed using Canonical Correspondence Analysis. Results show a close relationship between species presence in these sites and the rainfall, temperature, continentality, density of rock outcrops, disturbance and elevation variables. We recorded 175 taxa, floristic similarity among summits was low, and only two species were shared among the three peaks. Although the highest number of species was recorded at Las Antenas, both, in the floristic inventory and on the sampling plots, it was at Huehuento where the highest number of species/m² was recorded. The alpine element is poorly represented in the Sierra Madre Occidental, composed mainly by Juniperus blancoi var. huehuentensis, Draba implexa, Micranthes mexicana, Bromus richardsonii, and some dwarf species of Sedum, Galinsoga, and Muhlenbergia.