Vegetation structural complexity uniquely captures competition between vascular plants and bryophytes over succession

Abstract

Vascular plants and bryophytes are among the first colonizers of deglaciated landscapes, thus playing fundamental roles in ecological succession. Understanding biotic interactions between these groups is essential for comprehending the emergence of diverse and complex ecosystems. Set within a 170-year primary succession gradient in a glacier forefield in the Austrian Alps, this study investigates interactions between vascular plants and bryophytes during early ecosystem development. Data on vegetation structural complexity, obtained through high-resolution 3D-laser scanning, were combined with estimates of local substrate diversity, and the taxonomic and functional composition of vascular plants. This integrated approach allowed us to obtain a mechanistic understanding on the competitive interactions shaping bryophyte diversity over the course of primary succession. Competitive interactions between vascular plants and bryophytes were uniquely detected through a metric of vegetation structural complexity, while traditional community metrics of vascular plant cover, richness, composition, and functional diversity, failed to reveal these patterns. Path analysis shows that increasing vegetation structural complexity homogenizes local habitat conditions and constrains the realized ecological niche of bryophyte species, while substrate diversity acts as a buffer against vascular plant dominance. This mechanism was quantified using ecological dispersion, a novel concept introduced in this study that estimates the variability of growth optima within a community. Synthesis: This study highlights the additional value of quantifying the structural properties of plant communities through 3D-laser scanning in explaining ecosystem dynamics. By demonstrating its applicability in grassland ecosystems under field conditions, it underscores the potential of high-resolution remote sensing to advance vegetation structural research. The findings establish vegetation structural complexity as a key factor shaping plant-plant interactions in grasslands, influencing both ecosystem development and biodiversity patterns. These insights may provide valuable guidance for succession-based restoration strategies.