BackgroundSoil microenvironmental variables showed an important key inαand β-tree diversity in Neotropical montane oak forest. Thus, understanding the microenvironment fluctuation at small-fragment effects on tree diversity is crucial in maintaining the montane oak ecosystems. In this study, we hypothesized that within a relatively small-fragment (151.63 ha), treeαand β-diversity fluctuate and specific soil microenvironmental factors could influence tree species diversity to answer three questions: Do treeαand β-diversity differ among transects, even in a short-distance between them? Do microenvironmental variables influence tree diversity composition that occurs within a relict Neotropical montane oak forest? Is there a particular microenvironmental variable influencing tree species-specific?MethodsWe established four permanent transects during a year in a relict Neotropical montane oak forest, we assessed tree diversity and specific microenvironmental variables (soil moisture, soil temperature, pH, depth litterfall and light incidence). This allowed us to evaluate how microenvironmental variables at small-fragment influenceαand β-tree diversity and tree species-specific.ResultsOur results showed thatα-diversity was not different among transects; however, β-diversity of tree species was mostly explained by turnover and soil moisture, soil temperature, and light incidence were the microenvironmental variables that triggered the replacement (i.e., one species by another). Those variables also had effect on tree species-specific: Mexican beech (Fagus mexicana), Quebracho (Quercus delgadoana), Pezma (Cyathea fulva), Aguacatillo (Beilschmiedia mexicana), Pezma (Dicksonia sellowianavar.arachneosa), and Mountain magnolia (Magnolia schiedeana).DiscussionOur results confirm our hypothesis related to β-diversity but not withα-diversity; however, the tree community structure of the diversity was similar among transects. Our study represents the first effort to evaluate and link the soil microenvironmental effect on treeαand β-diversity, finding a high replacement in a small-fragment of Neotropical montane oak forest from eastern Mexico.