Functional structure of riparian vegetation across ecoregions: context-dependent trait patterns and implications for restoration

Abstract

Riparian forests are key ecological interfaces shaped by strong hydrological disturbance and geomorphological processes, yet their functional structure across broad environmental gradients remains poorly understood. We analyzed the functional structure of riparian vegetation across humid (Yungas) and semiarid (Western Chaco) ecoregions in northwestern Argentina to evaluate patterns of community assembly and propose functional targets for restoration. We sampled woody and herbaceous vegetation in riparian and adjacent forest sectors across ten sites and characterized twelve plant functional traits using a trait-based approach. Functional structure was assessed using multivariate analyses based on community-weighted means. Both ecoregion and habitat sector significantly influenced functional composition, with ecoregion explaining a larger proportion of variation. Contrary to expectations of broad-scale functional convergence, riparian communities exhibited distinct functional trait syndromes associated with regional climatic and geomorphological contexts. However, consistent differentiation between riparian and adjacent habitats was observed across ecoregions, indicating that local environmental filtering operates similarly within each region. Riparian habitats were characterized by deciduous phenology, low wood density, and anemochory dispersal trait, whereas adjacent forests were associated with evergreen phenology and autochory. These results indicate that environmental filtering in riparian systems is scale-dependent and context-specific, reflecting the interaction between fluvial disturbance and regional environmental constraints. The absence of a universal functional template highlights the need for regionally adapted restoration strategies. We propose a functional reference model that integrates hydrogeomorphological and ecological context to guide riparian restoration across contrasting ecoregions.