Altitudinal Patterns and Changes in the Composition of High Mountain Plant Communities

Abstract

Sierra Nevada, comprising 2348 vascular flora taxa (including 95 endemic taxa) is considered one of the most important plant hotspots within the Mediterranean region. Sierra Nevada presents 362 taxa inhabiting the alpine area (ca. 242 km2), 75 endemic species (62 endemic plus 13 sub-endemic) among them, constituting ca. 79% of the endemism of the entire area. This high-mountain has preserved many species, allowing the current presence of many artic-alpine species, including twelve cold-adapted species with their southernmost limit here. There are 23 nano-hotspots, most of them occurring at the highest altitude, at the coldest parts. Altogether, they host 30% of the Baetic endemic flora in just 0.07% of the area. Plant communities are also original, and they are composed of a mixture of Alpine and Mediterranean species. Climate change is strongly impacting alpine biota leading to an adaptation to the new conditions. When this adaptation capacity is overcome species are forced to migrate to avoid extinction. Some responses are already noticeable in alpine areas, such as: phenological changes, altitudinal movements, increasing competition and hybridization, and changes in plant assemblages. Direct impact related to human activities such as livestock grazing, use of fire to manage alpine pasturelands, mountain agriculture, outdoor activities, and infrastructure construction have additive effects to climate change, and altogether they can exacerbate negative changes. Monitoring, evaluating, and understanding the effect of global change in the Mediterranean mountains is a top priority. We offer guidelines to orient the conservation agenda at Sierra Nevada: To (i) establish an early warning indicators system, (ii) preserve plant species and habitats, (iii) preserve threatened plant species ex situ, (iv) promote adaptive management measures, (v) evaluate outdoor recreation activities, and (vi) control and regulate activities.