Conclusion
Understanding the development of communities in primary successions remains a major task of ecological studies. Our study suggests that, even though time since glacier retreat is a more important driver than depth in shaping the diversity of communities, patterns are not identical for superficial and deeper samples. This can have important consequences on ecosystem functioning, for example for the sequestration of organic carbon in these soils (Khedim et al., 2021). Nevertheless, differences between depths tend to decrease through time with a consistent pattern in both microorganisms and animals, possibly because of the increasing role of plants along successional stages. Future studies are required to identify possible factors driving biotic colonization within the same system (e.g. microclimate, soil features, etc.) and patterns of biotic interactions.