Ox-eye daisy (Leucanthemum vulgare Lam.) invasion has only a small effect on the diversity of a subalpine grassland

Context Ox-eye daisy (OED; Leucanthemum vulgare) has invaded subalpine communities in Australia. Aims We evaluated the effect of OED on subalpine grassland diversity in Kosciuszko National Park through addition and removal experiments. Methods In 2023 and 2024, we conducted two experiments on grassland that had been partly invaded by OED: (1) addition of OED seed to uninvaded plots, hypothesised to reduce α– and β-diversity; and (2) removal of OED plants by herbicide treatment and hand-pulling, hypothesised to temporarily reduce diversity. After 3 years, half the plots were slashed to mimic fire disturbance. We used generalised additive models to assess the treatment effects on diversity. Key results α-diversity increased and β-diversity decreased over time, regardless of the treatment. In disturbed plots where OED was added, OED had a negative effect on plot richness and diversity of rosette forbs. The effect on β-diversity was positive. When OED plants were removed, there was a temporary reduction in α-diversity following herbicide application with most measures returning to pre-treatment levels after 11 years. However, Xerochrysum subundulatum (a native forb) was severely affected by herbicide and did not recover fully. Conclusions OED affected grassland diversity, possibly through an allelopathic effect on recruitment. Despite OED abundance, the grassland community appeared resilient to invasion when undisturbed. Herbicides had a lasting effect on few native species. However, repeated applications will be required to prevent OED re-invasion. Implications The slow decline in α-diversity following OED invasion means that managers of subalpine grassland have time to address negative impacts on threatened species. Prevention and rapid response remain the most critical tools for OED management.