Using priority effects for grassland restoration: Sequential sowing can promote subordinate species

Aims: The influence of priority effects on plant community succession is increasingly discussed in community ecology. However, most grassland restoration approaches involving seed addition transfer all target species at the same time. Our objective was to tackle the question: does the order of arrival influence the establishment of restored communities?Location: La-Batie-Neuve, Southern Alps, France.Methods: We applied sequential sowing using two groups, one set of dominant species and one set of subordinate species, each comprising three different perennial plant species. We tested four sowing treatments: control (without any sowing), two sequential sowing treatments (dominants first or subordinates first) and synchronous sowing. We analysed plant cover each year for three years after sowing and calculated priority and earliness indices (the third year) for each group and each sown species.Results: Manipulating the order of arrival shaped community composition and trajectories. Some species of both groups were positively affected by being sown first compared to being sown synchronously. However, dominant and subordinate groups differed in their earliness index, showing a significant benefit for subordinates to be sown first. The subordinate species Onobrychis viciifolia and Plantago lanceolata established only when they were sown first, while Festuca cinerea showed greater establishment when sown first and simultaneously, compared to late sowing. The dominant Anthyllis vulneraria was not affected by date or type of sowing. However, the cover of the most dominant Bromopsis erecta was lower when being sown second, allowing a control of its dominance by delayed sowing.Conclusion: The strength of priority effects differs between species, which may depend on niche characteristics or microenvironment, influencing (negatively or positively) the establishment of late-arriving species and affecting their competitive abilities. Our study provides evidence that plant community assembly was influenced by the order of arrival, but demonstrated a strong species-specific response to priority effects.