Interactions among vascular plants, bryophytes, and lichens in grassland communities along elevational gradients.

Grasslands in temperate Europe are key biodiversity hotspots, supporting not only a rich vascular flora but also diverse communities of bryophytes and lichens. However, the processes shaping lichens and bryophytes in these ecosystems, particularly along environmental gradients, remain understudied. We investigated the relative roles of abiotic factors (elevation and rock abundance) and biotic drivers (vascular plant cover and height) in determining both the taxonomic and functional diversity of bryophytes and lichens in two protected grassland sites in central Italy. Across 80 plots spanning wide elevational gradients, we measured species richness and functional diversity for both bryophytes and lichens, and applied piecewise structural equation modeling to test causal relationships. Our results revealed that vascular plant structure (particularly vegetation cover and height) was the main determinant of lichens and bryophytesdiversity. Both facets of diversity in bryophytes and lichens were negatively affected by dense and tall vascular vegetation, likely due to shading and competition for space. Abiotic factors, such as elevation and rock abundance, influenced lichens and bryophytesonly indirectly, by altering vascular plant structure. An exception was bryophyte species richness, which was directly promoted by rock abundance through increased habitat heterogeneity and reduced vascular plant competition. Site-specific effects, likely related to substrate type (calcareous vs. siliceous), also played a significant role, particularly in shaping bryophyte communities. These findings suggest that biotic interactions, especially competition with vascular plants, play a more central role than direct abiotic filtering in determining lichens and bryophytesdiversity in grassland ecosystems. Our study provides a functional, multi-taxa framework for understanding elevational patterns of lichens and bryophytesdiversity and highlights the importance of considering vegetation structure in grassland conservation and management strategies.