SEEDLING DYNAMICS AT ELEVATION LIMITS: COMPLEX INTERACTIONS BEYOND SEED AND MICROSITE LIMITATIONS

Premise of the study: Limited availability of seeds and microsites are important constraints for seedling emergence and survival. However, little is known about population-level feedbacks between seed and microsite limitation and how these relationships vary in contrasting conditions. Focusing on Armeria caespitosa, a high-mountain endemic, we asked whether seedling establishment was simultaneously limited by seed and microsite availability, whether the balance between seed and microsite limitations varied with contrasting environments, and whether seed and microsite limitations interacted with each other. Methods: We studied seedling emergence and survival at the edges of the elevation range of A. caespitosa in central Spain over 4 years. We used mixed linear models and structural equation modeling. Key results: Our results showed that A. caespitosa recruits similar numbers of new seedlings per plot in contrasting environments. Seedling emergence and survival in A. caespitosa were both limited by seed and microsite availability. Habitat suitability (the surrogate of microsite limitation) varied between populations and indirectly affected fertility (the surrogate of seed limitation). Conclusions: Seedling emergence and survival are both seed and microsite limited, there are interactions between seed and microsite limitations, and both factors, which control seedling establishment, and their interconnections, vary among local populations.