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Mechanisms explaining patterns of biodiversity along elevation gradients in tropical mountain systems remain controversial. We use a set of climatic, topographic, and soil variables encompassing regional, landscape, and local‐level spatial scales to explain the spatial variation of tree species diversity in the Sierra Madre of Chiapas, Mexico. We sampled 128 circular plots (0.1‐ha each) in four elevational bands along four elevation gradients or transects encompassing 100–2200 m. A total of 12,533 trees belonging to 444 species were recorded. Diversity patterns along the elevation gradient and the explanatory power of independent variables were dependent on spatial scale (regional vs transect) and functional group (total vs late‐successional or pioneer species). Diversity of all species and late‐successional species (1 – proportion of pioneer species) showed a constant pattern at the regional and transect scales, with low predictive power of climatic variables and/or elevation. A linear decrease in either number or proportion of pioneer species diversity was observed with increasing elevation, which was correlated with temperature, rainfall, and human disturbance trends. Total species diversity showed an increase with rainfall of the warmest quarter, indicating a regional‐level limiting effect of seasonality (drought duration). Yet the explanatory power of climatic and topographic variables was higher at the individual transect level than at the regional scale, suggesting the parallel but differential influence of evolutionary and geological history factors on diversification not so far studied to explain elevation patterns of species diversity in tropical mountain systems.

Resumen: Se realizó un listado florístico para el Cerro Quetzal (Polígono III) y zonas adyacentes de la Reserva de la Biosfera El Triunfo, Chiapas, México. Se integró una base de datos con 1,513 registros, incluye 140 familias, 432 géneros, 795 especies y 24 categorías infraespecíficas. El total de las especies registradas en este trabajo representa 9% de la flora conocida para Chiapas y aproximadamente un 26.5% de la flora estimada para El Triunfo. El número de especies es similar a las encontradas en los polígonos I y II (751 y 791 especies, respectivamente) y mayor al cerro Cebú (polígono V) (502 especies). Los tipos de vegetación presentes en el cerro Quetzal son: bosque de coníferas, bosque mesófilo de montaña, bosque tropical perennifolio, bosque tropical subcaducifolio y vegetación ruderal. El tipo de vegetación más importante por el número de especies y mejor recolectado es el bosque mesófilo de montaña. Este listado presenta novedades, como una especie nueva del género Ceratozamia (Zamiaceae) y una de Sterculia (Sterculiaceae), además de dos registros nuevos para Chiapas, una de la familia Araceae (Monstera dubia) y otra de la familia Fabaceae (Albizia carbonaria). Palabras clave: bases de datos, conservación, diversidad florística, Sierra Madre de Chiapas.Abstract: A floristic checklist was made for Mt. Quetzal (Polygon III) and adjacent areas at the Triunfo Biosphere Reserve, Chiapas, Mexico. A database of 1,513 specimens was created comprising 140 families, 432 genera, 795 species, and 24 infraspecies. The total number of species recorded in this study represented about 9% of the estimated flora of Chiapas and nearly 26.5% of the estimated flora for The Triunfo region. The number of species is also similar to that recorded for polygons I and II (751 and 791 respectively) but higher than Mt. Cebú (Polygon V) (502 species). The vegetation communities determined in the Mt. Quetzal were: conifers forest, cloud forest, tropical rain forest, subdeciduous tropical forest, and ruderal vegetation. The vegetation type more important based on the number of species and the best recollected was the cloud forest. This checklist also included novel taxa: a new species of Ceratozamia (Zamiaceae) and a new species of Sterculia (Sterculiaceae) and the presence Monstera dubia (Araceae) and Albizia carbonaria (Fabaceae) unrecorded for Chiapas.

Resumen: Se realizó el inventario florístico del Parque Nacional Cañón del Sumidero, Chiapas, México. Treinta y tres salidas de campo se hicieron de 2007 a 2008 y se consultaron y revisaron bases de datos de herbarios. Se registraron 1,298 especies, 632 géneros, 135 familias y 58 infraespecies. Las familias más representativas corresponden a Fabaceae (126 especies y 52 géneros) y Asteraceae (107 especies y 65 géneros). Los géneros más diversos fueron Ipomoea (18), Tillandsia (17) y Peperomia (16). Además, 625 especies se clasificaron como hierbas y 1,179 especies como autótrofas. El bosque tropical caducifolio fue el más diverso con 30.91% de las especies reportadas. Dentro de alguna categoría de riesgo dentro de la NOM-ECOL-059-2010 se registraron 24 especies y 2.6% de la flora del Cañón del Sumidero es endémica de Chiapas. Dos especies, Valeriana palmeri A. Gray y Dioon sp., posiblemente están extintas en el área de estudio. Palabras clave: área natural protegida, base de datos, bosque tropical caducifolio, endemismo, riqueza. Abstract:A floristic inventory was conducted in the Sumidero Canyon National Park, Chiapas, Mexico. Thirty-three field trips were conducted from 2007 to 2008 and the revision of herbaria data bases. About 1,298 species and 58 infraspecies were recorded among 632 genera and 135 families. The most representative families were Fabaceae (126 species with 52 genera) and Asteraceae (with 107 species and 65 genera). The most diverse genera were Ipomoea (18), Tillandsia (17), and Peperomia (16). In addition, 625 species were classified as herbs and 1,179 species were terrestrial autotrophic. Tropical deciduous forest was the most diverse with 30.91% of the species reported. About 24 species were recorded under some level of threat-risk within the official threatened species list NOM-ECOL-059-2010 and 2.6% of the flora reported in the Sumidero Canyon is endemic to Chiapas. Two species, Valeriana palmeri A. Gray and Dioon sp., are thought possibly extinct in the study area.