Global glacier retreat is rapidly exposing vast terrains of bare ground, leading to the emergence of postglacial ecosystems. The success of this emergence will determine the future of a substantial fraction of alpine biodiversity and associated ecosystem services. Plant-plant facilitation is a key ecological mechanism structuring alpine communities, yet its effectiveness across latitudes and postglacial ecosystems remains unclear. We compare the direction and intensity of plant-plant interactions between temperate and tropical postglacial terrains shortly after glacier retreat. We conducted a bi-continental field study at one temperate site (France) and two tropical sites (Bolivia, Peru), and quantified plant–plant interactions in recently deglaciated areas (0-30 years and 30-60 years since glacier retreat). At each site, we identified the most abundant species and estimated their effects on local plant communities using the Relative Interaction Index (RII) across 320 paired plots. We observed net facilitation in the tropical sites (RII = 0.12***) but net competition in the temperate site (RII = -0.10***). Across sites, interactions shifted significantly from facilitation to competition between 0-30 and 30-60 years since glacier retreat. Species canopy volume was a strong positive driver of facilitation, with the most effective facilitators being large life forms, such as erect shrubs and giant tussock grasses, which are present only in the tropics. In accordance with the stress-gradient hypothesis, the greater facilitation observed in tropical areas can be attributed to the higher stress that plants experience, particularly from extremely cold nighttime temperatures due to low climatic seasonality and the absence of snow. Tropical environments condition the development of larger life forms that are especially effective at facilitating other species. As organic matter accumulates over time, it reduces environmental stress, potentially explaining the shift from facilitation to competition in older deglaciated areas.