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Mediterranean mountains are extraordinarily diverse and hold a high proportion of endemic plants, but they are particularly vulnerable to climate change, and most species distribution models project drastic changes in community composition. Retrospective studies and long-term monitoring also highlight that Mediterranean high-mountain plants are suffering severe range contractions. The aim of this work is to review the current knowledge of climate change impacts on the process of plant regeneration by seed in Mediterranean high-mountain plants, by combining available information from observational and experimental studies. We also discuss some processes that may provide resilience against changing environmental conditions and suggest some research priorities for the future. With some exceptions, there is still little evidence of the direct effects of climate change on pollination and reproductive success of Mediterranean high-mountain plants, and most works are observational and/or centred only in the post-dispersal stages (germination and establishment). The great majority of studies agree that the characteristic summer drought and the extreme heatwaves, which are projected to be more intense in the future, are the most limiting factors for the regeneration process. However, there is an urgent need for studies combining elevational gradient approaches with experimental manipulations of temperature and drought to confirm the magnitude and variability of species′ responses. There is also limited knowledge about the ability of Mediterranean high-mountain plants to cope with climate change through phenotypic plasticity and local adaptation processes. This could be achieved by performing common garden and reciprocal translocation experiments with species differing in life history traits. [ABSTRACT FROM AUTHOR]

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.

Frequency-dependent processes are relevant for flowering plant reproduction, especially for species with disassortative mating. In an individual-based study, we tested not only the effects of local density on reproductive success at small spatial scales, but also those of neighborhood quality. To test the neighborhood effects on the reproduction of Armeria caespitosa, a dimorphic Mediterranean high-mountain endemic, we introduce a novel pollination context (PC) index that considered the distance, floral display, and floral morph of neighbors at small scales (within 2 m from the focal plant), studying rock and pasture populations at both edges of the species altitudinal distribution. Reproductive success depended significantly on PC only at the low populations, suggesting that the PC effects are population-dependent and supporting the hypothesis that the neighborhood quality influences the reproductive success of A. caespitosa at least in stressful conditions. Moreover, fruit set was morph-dependent in the high-pasture population. The specific role of the spatial structure of compatible vs. incompatible morphs at small scales of the dimorphic self-incompatibility system in Armeria deserves further attention. Parameters other than plant density are useful for the study of small-scale density-dependent processes that affect pollination and other reproductive components, especially if they integrate neighborhood quality information at adequate spatial scales.