Spatial scale dependence of plant functional diversity and its response to land-use intensity in grassland farming systems

Land use effects on plant functional diversity have so far been primarily analysed at the local plot scale in semi-natural grassland fields. However, farms represent a focal spatial scale as farmer-specific management decisions across several fields shape the regional trait space. To better understand the scale dependency of plant functional diversity while accounting for regional context, we examined (i) its magnitude across the plot, farm and regional scale and the impact of land-use intensity (ii) at both the plot and farm scale as well as (iii) on farm-to-regional functional dissimilarity in three temperate regions of Central Europe. We quantified functional diversity based on three leaf traits, applying Carmona et al.'s trait probability density framework that incorporates intraspecific variability. Our results show that functional richness increased and divergence decreased from the plot to the farm scale, while evenness showed a unimodal trend across scales. Despite incorporating within-farm heterogeneity by aggregating plot data to the farm scale, hump-shaped effects of grazing and fertilisation on functional richness remained detectable in some regions, but effects were weak and similar to the plot scale. Furthermore, farm-to-regional functional dissimilarity was negatively correlated with farm-level functional richness and consequently increased if farms were grazed very little or not at all. Our findings highlight that farm-to-regional functional dissimilarity, when used in conjunction with farm-level functional richness, can help identify farms with a variety of complementary plant strategies contextualised for a region. This could support conservation planning and assessing the success of eco-schemes implemented within the Common Agricultural Policy.