1. Natural selection drives how organisms allocate resources among competing demands such as growth, reproduction, and survival. In ferns, where reproductive and vegetative organs share developmental pathways, these trade-offs may be particularly strong under environmental disturbance. 2. This study investigates how the rare fern Ophioglossum vulgatum allocates resources between vegetative growth and reproduction in response to vegetation removal (mowing) and simulated herbivory (clipping). 3. A field experiment was conducted in wet meadow and peatland habitats in central Poland using a factorial design. Four treatments were applied: control, clipping, mowing, and clipping combined with mowing. Across ten transects, 533 ramets were marked and monitored. 4. Biometric measurements included leaf blade area, sporophore length, number of sporangia, and plant height. Data were analyzed using two-way ANOVA with clipping and mowing as fixed factors. 5. Key results: • Mowing significantly reduced plant height and leaf blade area, but only in unclipped plants (significant clipping × mowing interaction). • Clipping alone, simulating herbivory, had no significant direct impact on any of the measured traits, although its interaction with mowing revealed important effects. • Control plots exhibited the greatest allocation to reproduction, with larger sporophores and more sporangia. • All treatments reduced reproductive output compared to controls, while vegetative performance remained stable or increased. • Ramet abundance increased across all treatments, suggesting resilience through clonal propagation. 6. These findings suggest that O. vulgatum exhibits trait-specific and context-dependent responses to disturbance. Reproductive traits are more sensitive than vegetative growth, and their suppression under mowing may limit reproductive success in managed habitats. 7. Conservation strategies should account for both short-term physiological responses and long-term demographic processes. Management practices, particularly mowing, should be carefully timed and scaled to avoid unintended negative effects on reproduction in rare ferns such as O. vulgatum.

1. Natural selection drives the allocation of resources between growth, reproduction, and other processes in organisms, especially under limited resource availability. 2. This study investigates how the fern Ophioglossum vulgatum L. allocates resources between photosynthetic growth and spore production under competition and simulated herbivory. 3. A large-scale field experiment was conducted in meadows and peatlands in Imielenko, Poland, involving 10 transects with three squares each. Four treatments were applied: clipping of O. vulgatum ramets, mowing surrounding plants, no intervention (control), combined clipping and mowing. 4. A total of 533 ramets were marked, and biometric parameters such as leaf blade area, sporophore size, and sporangia number were recorded and analyzed. 5. Key findings: • Mowing increased leaf blade area but reduced sporophore size and sporangia production in the following year. • Control plots displayed the highest resource allocation to reproduction, with larger sporophores and more sporangia compared to treated plots. • Clipping and mowing negatively impacted reproductive allocation, reflecting a trade-off in resource distribution. • Simulated herbivory did not significantly influence growth or reproduction, suggesting resilience to herbivory. 6. The results demonstrate that mowing alters resource allocation patterns, prioritizing photosynthetic growth at the expense of reproduction. 7. These findings highlight the importance of management practices, such as controlled mowing, in maintaining population persistence of rare ferns like O. vulgatum. 8. Implications for conservation: • Balancing growth and reproduction through tailored management strategies can support the conservation of O. vulgatum in meadow-wetland ecosystems. • The resilience of O. vulgatum to herbivory underscores its adaptive potential, but care must be taken in applying treatments that could disrupt natural resource allocation.