Structural shifts in plant functional diversity during biogeomorphic succession: Moving beyond taxonomic investigations in an alpine glacier foreland

Abstract

The complex interrelation between plants and geomorphic processes is described in the concept of biogeomorphic succession. While ecological research on succession and community assembly has transitioned towards functional approaches, studies on functional diversity in biogeomorphic settings, particularly in glacier forelands, remain limited. In this study, we investigated abundance of vascular plant species and functional traits in an alpine glacier foreland using data from 199 plots. Our objective was to unravel the development of functional diversity during biogeomorphic succession. Specifically, the study determined whether structural shifts in functional diversity are associated with stability thresholds related to plant cover, geomorphic influence, and examined trait spectra for stages of biogeomorphic succession. Our findings revealed a nonlinear trajectory of functional diversity along the plant cover gradient, marked by two distinct structural shifts at 30% and 74% cover, corresponding to established stability thresholds. Along the gradient of geomorphic influence, we observed an increase in functional diversity until 54% of the plot area was affected, beyond which functional diversity declined below the initial level. The analysis of community-weighted means of traits across four stages of biogeomorphic succession determined by plant cover and absence and presence of geomorphic influence revealed significant differences in trait values. In the transition to the biogeomorphic stage, associated with the identified initial structural shift, there is a shift from a prevalence of above-ground adaptation and reproductive traits, such as leaf longevity, structure, growth form and mixed reproductive strategies, to an increased dominance of competitor species and traits related to below-ground structures, including root type and structures, as well as vegetative reproduction. Our results contribute to understanding the relationship between vegetation succession and geomorphic influence by linking them to plant functional traits. This study advances beyond traditional taxonomic investigations by emphasizing functional approaches to biogeomorphic succession. Moreover, the functional trait data used in this study, easily downloadable from a public repository, can serve as a valuable template for future research in (bio)geomorphology, along with the employed methodologies.