Aim: Global biodiversity loss resulting from anthropogenic land-use activities is a pressing concern, requiring precise assessments of impacts at large spatial extents. Existing models mainly focus on species richness and abundance, lacking insights into ecological mechanisms and species' roles in ecosystem functioning. To bridge this gap, we conducted an extensive analysis of the impact of human land use on vascular plant functional diversity, across diverse land-use classes and bioregions in Europe, comparing it to traditional metrics. Location: Europe           Time period: 1992-2019                           Major taxa studied: Vascular plants Methods: Integrating extensive databases of vegetation plots with spatial data on land use and land cover, we paired plots from areas actively used and modified by humans with plots from natural habitats under similar environmental conditions. Using species occurrences and traits, in each plot we computed three complementary functional diversity metrics (functional richness, evenness, and divergence), species richness and abundance. We assessed the impact of land use by comparing the metrics in the paired plots. Results: Our findings revealed that, compared to natural habitats, anthropogenic land use exhibits lower functional richness and divergence but higher functional evenness across most land-use classes and bioregions. The response of functional richness was more marked than the other two metrics and especially pronounced in croplands and urban areas and in northern bioregions. Functional richness exhibited a pattern that did not fully overlap with the trend in species richness, providing useful complementary information. Main conclusions: We provide a large-scale precise assessment of anthropogenic land-use impacts on functional diversity across Europe. Our findings indicate that: (i) human disturbance significantly alters plant functional diversity compared to natural habitats; (ii) this alteration goes in the direction of functional homogenization within sites; (iii) functional diversity metrics complement traditional metrics by offering deeper insights into the ecological mechanisms in response to anthropogenic land use.

1. Forest regrowth following farmland (agriculture and pasture) abandonment has been positively associated with a number of processes including the regulation of hydrological cycling, the enhancement of soil functioning, and an increase in forest productivity and carbon (C) sequestration. Although these changes in ecosystem functioning post-farmland abandonment have been observed in multiple locations and studies, the ecophysiological basis underpinning these patterns remains unclear. Here, we examine whether increased forest expansion following pastureland abandonment is associated with greater water-use efficiency (WUE) and legacies from previous land use in terms of nitrogen (N) availability. 2. We thus explored differences in leaf traits and N availability between recently established (post-1950) beech (Fagus sylvatica L.) forests on former pastureland and long-established beech forests (pre-1950). The investigated leaf traits were leaf specific area (SLA), leaf N concentration (%N) and intrinsic WUE (iWUE, i.e. the ratio between photosynthesis and stomatal conductance); as well, leaf and soil stable N isotope composition (δ15N) and total %N were used to assess changes in N availability. Finally, we compared the correlation strength between the above-mentioned parameters and those associated with tree productivity (wood density and basal area increment, BAI) and the richness of ectomycorrhizal fungi (ECM) in these two forest types. 3. Recent forests had greater iWUE than long-established forests, which was associated more with lower SLA than leaf %N. Leaf and soil δ15N were more robust proxies than %N for detecting differences in N availability. Less negative leaf and soil δ15N values in recent vs. long-established forests suggest, on one hand, greater N availability, probably due to higher historical N input originating from animal excreta on these former pasturelands, and, on the other, an increase in N loss pathways. 4. Our results point to greater correlations between leaf δ15N, tree iWUE, and productivity in recent forests than in long-established forests, thereby suggesting a close link between C and N cycles. Our findings also highlight different N dynamics between the two forest types, with recent forests showing ‘leaky’ N cycling wherever lower N retention by trees and associated ECM fungi occurs as a legacy of previous land use.