Coexistence despite competition: Bryophyte diversity is buffered against vascular plant dominance over succession

Abstract

In alpine landscapes, vascular plants and also bryophytes are key biological features shaping the trajectories of primary succession following glacial retreat. Yet research on ecological successions is mainly centered around vascular plants, and potential interactions between both taxonomic groups have been largely disregarded. In this study, we examine successional processes impacting both groups across a 170-year gradient developing into a natural grassland ecosystem in the Austrian Alps. Utilizing multispectral 3D whole community phenotyping and introducingecological dispersionas a metric reflecting a community’s ecological, calculated as the dispersion of ecological indicator values, we gain a mechanistic understanding of the interactions between bryophyte and vascular plant diversity along grassland succession. Our findings show an increase in diversity for both groups over time, with vascular plants demonstrating a transitional community composition pattern along the successional gradient. Bryophytes, in contrast, do not show a consistent pattern of community compositional change over succession and are less affected by microclimate and soil nutrients, highlighting opportunistic colonization strategies with bryophyte communities showing increased ecological dispersion over time. Structural equation modeling reveals that vascular plant growth structure, quantified via digital community features from multispectral 3D plant scanning, negatively affects bryophyte diversity and ecological dispersion, suggesting competitive interactions with vascular plants. Our research underlines the complex dynamics between bryophyte and vascular plant communities during alpine grassland succession and stresses the importance of including both groups in succession studies to fully grasp biodiversity development and succession mechanisms.