Authors: Carrié, Romain; Ekroos, Johan;Smith, Henrik;

Studying the impact of farming practices on the resilience of biodiversity to extreme climatic events is key to design sustainable farming systems in a changing climate. However, longitudinal studies monitoring the response and recovery of biodiversity to extreme climatic disturbance such as droughts are lacking in real-world farms. Here, we monitored 10 organic and 9 conventional farms over a period of 5 years covering an extreme drought event in 2018. We surveyed in-field flowering plant communities over the years (in cereals, leys and semi-natural grasslands). We expected that organic farming would promote resilience against drought due to higher levels of pre-drought plant diversity and practices promoting water holding capacity of soils, due to higher soil organic matter. We detected a decrease in plant species richness of 34% and 24% in leys and semi-natural grasslands respectively during the drought compared to the previous year, while species richness remained stable in cereals. Rare plant species were more likely to be lost than common (abundant) species. Organic farming did not affect the loss of plant species relatively to pre-drought levels of species richness. Practices such as soil tillage, not bound to organic management, might drive plant species loss to a higher extent.