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Studying community phylogenies along elevation gradients can inform us about the influences of environmental conditions on the structuring communities, and therefore allow predictions on how future environmental changes may affect them. The aim of the work was to evaluate the processes that govern tree communities along an altitudinal gradient in an upper montane Atlantic Forest in the Mantiqueira Range, southeastern Brazil. To do so, we analyzed the phylogenetic structure of angiosperm tree communities in four elevations (ranging from 1500 to 2100 m) and verified if it varies significantly with altitude. We also analyzed the phylogenetic beta diversity among local angiosperm tree communities along the altitudinal gradient. Further, we evaluated the soil and temperature influences over these communities. The results showed tendency of increasing phylogenetic clustering with the elevation. We also verified that the phylogenetic lineages of the tree communities are replaced along the altitudinal gradient influenced by changes in temperature and soil, indicating phylogenetic niche conservatism. This suggest that these communities could move to higher altitudes in a global warming scenario, and that would change their species composition and abundance due to changes in soil along the altitudinal gradient. Thus, the highest areas would be threatened as they would not have higher altitude locations to migrate to. In addition, phylogenetic lineages which only occur, or occur in their large majority, at highest altitudes (i.e., Cunoniaceae and Winteraceae) would be locally extinct by the current (or future) climatic scenario.

Species–habitat associations can be used as a proxy for species niches. Previous research has shown that niche plasticity may increase diversity in plant communities, and that plasticity may be linked to variations in species fitness. Spatial and temporal aspects of the niche are of interest to understand community structure, but the temporal dimension is often difficult to incorporate in ecological research. In this study, we investigated if species–habitat associations are stable across time, and if they are not, whether niche plasticity promotes variations in species fitness and increases in diversity. We modeled the representativity of 36 species as a function of soil variables and slope in an Atlantic tropical wet forest located in southeast Brazil, as well as their interactions with time, monitored over a period of 17 years. We found niche plasticity to be a common mechanism among the studied species in the studied time period. Niche plasticity was neither significantly related to variations in species fitness nor to changes in species richness, but had a negative effect on diversity when species abundance was accounted for (Shannon and Simpson indexes). We were able to make relevant observations of species–environment relationships over time, such as their niche stability and its effects on the community. We argue that this knowledge is useful in a context of climate change for revealing mechanisms used by plants to cope with environmental oscillations.