Mast seeding mitigates the negative demographic effects of conspecific adults on rowan seedling survival

Abstract

Background and Aims Seedling mortality filters tree recruitment, yet we know little about whether the year in which a seedling is produced leaves a demographic signal after emergence. This gap is central for mast-seeding species, where seed crops vary widely among years and may generate cohorts that differ in offspring quality. We tested whether the size of the seed crop from which a seedling cohort comes predicted subsequent seedling survival, and whether this effect depended on seedling size, age, and conspecific neighbourhood context. Methods We used 15-years of data monitoring the establishment, survival and growth of 4678 individually marked rowan (Sorbus aucuparia) seedlings in a natural subalpine spruce forest in West Carpathians. We modelled annual survival in relation to seedling age, leaf area, crop size, and establishment beneath conspecific rowans or heterospecific spruces. Key Results Seedling survival increased with age, leaf area, and establishment beneath heterospecific spruces compared with conspecific rowans. The effect of crop size depended on neighbourhood context. Beneath the crowns of conspecific rowans seedlings from high-crop years survived better than seedlings from low-crop years, whereas survival beneath heterospecific spruces changed little with crop size. As a result, the seedling survival disadvantage associated with establishment beneath conspecifics was reduced for cohorts from high-crop years. Conclusions Masting can shape recruitment beyond seed production and seedling emergence by influencing the survival of established cohorts. Our results suggest that variation in cohort quality among years may determine how many seedlings pass through the establishment bottleneck. By increasing survival in conspecific neighbourhoods, high-crop years may also alter the spatial pattern of recruitment, allowing more seedlings to persist near conspecifics.