Ecological mechanisms that maintain species identity between potentially interfertile sympatric populations are puzzling. Local adaptation to a particular environment by means of phenology may confine plants to very specific habitats that may result in assortative mating within an initially panmictic population. Nothofagus pumilio, N. antarctica and N. dombeyi are sister species. They can occur in sympatry and are known to interbreed but they are morphologically and ecologically different. We recorded leafing and flowering phenologies and their thermal requirements to reach each phenophase at distinct locations during three growing seasons (2016–2018). We compared data for sympatric and allopatric populations of different species, sites and elevations. Sympatric populations of different species have contrasting thermal requirements and thus uncoupled phenologies. Temperature, through differences in elevation, is the main driver of intraspecific phenological differences at the population level. Low elevation populations flower earlier than high elevation ones. Allopatric populations of each species are synchronic and reproductively linked to some degree. A combination of high ecological specialization and strong phenological pre-pollination barriers operate together to temporally isolate distinct species, against the homogenizing effect of the occasional or even persistent gene flow. The eventual hybrid formation could be negatively selected by strong local selection to contrasting environments.

在可能不育的同域种群之间保持物种同一性的生态机制令人费解。通过物候学对特定环境的局部适应可能会将植物限制在非常特定的栖息地，这可能导致最初恐慌的种群内进行分类交配。Nothofagus pumilio , N. antarctica和N. dombeyi是姐妹种。它们可以同时发生并且已知可以杂交，但它们在形态和生态上是不同的。我们记录了在三个生长季节（2016-2018）期间到达不同位置的每个物候期的生叶和开花物候及其热需求。我们比较了不同物种、地点和海拔的同域和异域种群的数据。不同物种的同域种群具有不同的热需求，因此具有不耦合的物候。通过海拔差异，温度是种群水平上种内物候差异的主要驱动因素。低海拔种群早于高海拔种群开花。每个物种的异域种群在某种程度上是同步的和生殖相关的。高度生态专业化和强大的物候预授粉障碍相结合，可以在时间上隔离不同的物种，抵抗偶尔甚至持续基因流的同质化效应。通过对对比环境的强烈局部选择，最终的混合形成可能会被负面选择。