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Under climate warming, plants will undergo novel selective pressures to adjust reproductive timing. Adjustment between reproductive phenology and environment is expected to be higher in arctic and alpine habitats because the growing season is considerably short. As early-and late-flowering species reproduce under very different environmental conditions, selective pressures on flowering phenology and potential effects of climate change are likely to differ between them. However, there is no agreement on the magnitude of the benefits and costs of early-vs. late-flowering species under a global warming scenario. In spite of its relevance, phenotypic selection on flowering phenology has rarely been explored in alpine plants and never in Mediterranean high mountain species, where selective pressures are very different due to the summer drought imposed over the short growth season. We hypothesized that late-flowering plants in Mediterranean mountains should present stronger selective pressures towards early onset of reproduction than early-flowering species, because less water is available in the soil as growing season progresses. We performed selection analyses on flowering onset and duration in two high mountain species of contrasting phenology. Since phenotypic selection can be highly context-dependent, we studied several populations of each species for 2 years, covering their local altitudinal ranges and their different microhabitats. Surrogates of biotic selective agents, like fruitset for pollinators and flower and fruit loss for flower and seed predators, were included in the analysis. Differences between the early-and the late-flowering species were less than expected. A consistent negative correlational selection of flowering onset and duration was found affecting plant fitness, i.e., plants that bloomed earlier flowered for longer periods improving plant fitness. Nevertheless, the late-flowering species may Electronic supplementary material The online version of this article (experience higher risks under climate warming because in extremely warm and dry years the earlier season does not bring about a longer flowering duration due to summer drought.

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 highmountain 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 0 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.

Reproduction at population lower edges is important for plant species persistence, especially in populations on contracting high-mountain islands. In this context, the ability of plants to reproduce in different microhabitats seems to be important to guarantee seed production in stressful environments, such as Mediterranean high mountains. We hypothesised that the warmer and drier conditions at the lower edge would be deleterious for the reproduction of Armeria caespitosa, an early-flowering plant. In addition, reproductive plasticity along this mountain gradient may also be microhabitat-dependent. We studied factors affecting the reproductive success of A. caespitosa, an endemic of the Spanish Sistema Central. We considered a complex set of predictors, including phenology, plant size and environmental factors at different scales using generalised estimating equations and generalised linear models. Microhabitat, together with the position in the altitudinal gradient and inter-annual variability affected the reproduction of A. caespitosa. In addition, individuals with longer flowering periods (duration of flowering) had significantly lower fruit set and a higher number of unviable seeds; delayed flowering peaks favoured the production of both viable and unviable fruits. Microhabitat variability over an altitudinal range is relevant for the reproduction of A. caespitosa, and is more important at the lower edge of the altitudinal range, where the species faces the most adverse conditions. In addition, the ability to reproduce in different microhabitats might increase the chances of the species to cope with environmental uncertainties under on-going climate warming. Finally, reproduction of this early-flowering plant is constrained by summer drought, which might shape its reproductive phenology.

Background: Under the current warming process, with its implications of higher temperatures, less rainfall, snowfall and snow cover, low-edge populations of high-mountain plants are expected to decline. Demographic studies are useful to foresee the future dynamics of species ranges. Adaptation, phenotypic plasticity, and demographic compensation have been proposed as mechanisms to cope with climate change. Aim: We studied the population dynamics of the high-mountain narrow endemic Armeria caespitosa at the extremes of its altitude distribution (low versus high edge), the high edge representing colonised summits that provide optimal growing conditions. The focus of the study was to establish if the species is retracting at its lower distribution range. Methods: We used 4 years of population censuses and soil seed bank data. Population matrix models allowed us to study the stochastic population growth rates, the species long-term viability under higher frequency of extreme years, and the life cycle transitions responsible for the differences in population dynamics between elevation range edges. Results: The low edge of the A. caespitosa elevation range appeared stable, with positive population growth rates under current environmental conditions, and a null quasi-extinction probability in the long-term under scenarios of high frequency of extremely dry years. Conclusions: The species will likely withstand the current climate-warming scenario along its elevation range. Results supported the role of so-called demographic compensation at a small spatial scale, which we argue might be common in the Mediterranean mountains.