Climate and management changes drove more stress-tolerant and less competitive plant communities in 40 years
Spontaneous plant communities have undergone considerable constraints due to human-mediated changes. Understanding how plant communities are shifting in response to land management and climate changes is necessary to predict future ecosystem functioning and improve the resilience of managed ecosystems, such as agroecosystems. Using Mediterranean weed communities as models of managed plant communities in a climate change hotspot, we quantified to which extent they have shifted from the 1980s to the 2020s in response to climate and management changes in vineyards. In four decades, the annual range of temperatures (i.e. the difference between the warmest months and the coldest months mean temperatures) increased by 1.2{degrees}C and the summer temperatures by 2{degrees}C. Weed management diversified over time with the adoption of mowing that replaced the chemical weeding of inter-rows. Current weed communities were 41% more abundant, 24% more diverse and with a less even distribution of abundance across species than the 1980s communities at the vineyard level. Modern communities were composed of more annual species (57% of annual species in the 1980s versus 80% in the 2020s) with lower lateral spreadability and seed mass and were composed of fewer C4 species. They had higher community-weighted specific leaf area, higher leaf dry matter content and lower leaf area than 1980s weed communities. At the community level, the onset of flowering was earlier and the duration of flowering was longer in the 2020s. Climate change induced more stress-tolerant communities in the 2020s while the diversification of weed management practices over time filtered less competitive communities. This study shows that plant communities are adapting to climate change and that land management is a strong lever for action to model more diverse and functional plant communities in the future.