Weed community change from the 1980s to 2020s, South France

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. The
weed communities of the same 40 vineyards in the Montpellier region were
surveyed using the same protocol in spring, summer, and autumn, for two
years, with a 40-year interval (1978-79 versus 2020-21). In four decades,
the annual range of temperatures (i.e. the difference between the warmest
month's and the coldest month's mean temperatures) increased by
1.2°C and the summer temperatures by 2°C. Weed management diversified over
time with the adoption of mowing that replaced the chemical weeding of
interrows. Chemical weeding is now mostly limited to the area under the
row. 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 community-weighted 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 the 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 favoured less ruderal
communities. This study shows that plant communities are shifting in
response to climate change and that land management is a strong lever for
action to model more diverse and eventually more desirable plant
communities in the future.