Soil depth, rather than altitude, better explains environmental filtering in the high-altitude-adapted Andean Páramos

Global change threatens mountainous plant communities, causing habitat displacement. Phylogenetic studies reveal evolutionary and ecological processes in community assembly. We examined taxonomic and phylogenetic diversity in Andean Páramos across altitudes. Our hypotheses were that increasing altitude is an environmental filter, as altitude is expected to be a stronger variable than soil depth. The Páramos, alpine vegetation in the Andes, range from 3,000 to 4,700 meters, with our plots spanning 3,200 to 4,100 meters. Sampling was conducted at six altitudinal levels, measuring soil depth, taxonomic, and phylogenetic diversity. Data analysis employed multiple linear regressions and mixed-effects models to assess the effects of soil depth and altitude. We sampled 110 angiosperm species from 70 genera, 30 families, and 18 orders. Asterales and Poales were prominent. Species richness generally decreased with altitude but increased at the summit. Soil depth affected species richness and taxonomic diversity, while altitude did not. Phylogenetic diversity increased with soil depth and decreased with altitude. Phylogenetic turnover increased with altitude differences. The hypothesis that increasing altitude intensifies environmental filtering in the altitude-adapted Páramos resulting in lower species richness and more clustered phylogenetic structures, was rejected. Although species richness, Shannon diversity, and Simpson diversity decreased initially with increasing altitude, this trend was not linear because the summit presented intermediate species richness. The hypothesis that altitude is a stronger explanatory variable than soil depth was also rejected. Despite expectations, taxonomic results did not support altitude as an environmental filter, but soil depth. Greater altitude differences increased beta phylogenetic dissimilarity, supporting niche conservatism.