Functional trade-offs: exploring the effects of climate change and agricultural practices as drivers of field margin plant communities

Abstract Over the past decades, agricultural intensification and climate change have led to vegetation shifts in Europe. However, functional trade-offs linking traits responding to climate and farming practices are rarely analyzed, especially on large-scale empirical studies. Here we used a standardized yearly monitoring effort of agricultural field margin flora at the national scale to assess the spatio-temporal response of diversity and functional traits to climatic and agricultural variations. We examined temporal trends in climate (temperature, soil moisture), intensity of agricultural practices (herbicides, fertilization, margin management), plant species richness, and community-weighted means and variances of traits expected to vary both with climate and practices (e.g. seed mass, specific leaf area), across 555 sites in France between 2013 and 2021. We found that temperatures have increased while soil moisture has decreased, reflecting current climate change, whereas the intensity of agricultural practices did not show clear temporal trends over the past decade. Functional changes in plant communities were significant, showing an increase of thermophilic species with a conservative resource acquisition strategy mainly explained by climate change. The impact of agricultural practices was more limited and mainly exerted through field margin management and fertilization that shifted vegetation towards species with a ruderal syndrome. Responses to climate change differed according to crop type (vineyards versus annual crops), region (Mediterranean versus continental), and species life cycle (annual versus perennial). Our findings suggest that species adapted to climate change (including Mediterranean and conservative species) have increased in proportion. Importantly, we identified functional trade-offs indicating that these species are also the most vulnerable to intensive agricultural practices, as they are less adapted to high levels of resources and disturbances. We put these results into the conceptual framework of Grime’s CSR triangle and revealed a decline of competitive and ruderal species in favor of stress-tolerant species better adapted to climate change. By choosing less intensive management, we can promote diverse communities with a wide range of CSR strategies, thereby increasing the presence of species adapted to climate change.