The Specific Vulnerability of Plant Biodiversity and Vegetation on Mediterranean Islands in the Face of Global Change Frederic Medail

The specific vulnerability of plant biodiversity and vegetation on Mediterranean islands in the face of global change Frederic Medail To cite this version: Frederic Medail. The specific vulnerability of plant biodiversity and vegetation on Mediterranean islands in the face of global change. Regional Environmental Change, Springer Verlag, 2017, 17 (6), pp.1775-1790. 10.1007/s10113-017-1123-7. hal-01681626 HAL Id: hal-01681626 https://hal.archives-ouvertes.fr/hal-01681626 Submitted on 7 May 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Reg Environ Change (2017) 17:1775–1790 DOI 10.1007/s10113-017-1123-7 REVIEW ARTICLE The specific vulnerability of plant biodiversity and vegetation on Mediterranean islands in the face of global change Fre´de´ric Me´dail1 Received: 5 October 2016 / Accepted: 3 February 2017 / Published online: 23 March 2017 Ó Springer-Verlag Berlin Heidelberg 2017 Abstract The numerous Mediterranean islands ([10,000) refugia’ to ensure the long-term preservation of coastal are very important from a biodiversity point of view, both plant biodiversity. They also represent fascinating ecolog- in term of plant species (numerous endemics, presence of ical systems to disentangle the role of environmental versus ‘climate relicts’) and of ecosystems’ assemblage. These human pressures on spatially simplified communities of the patterns can be explained by complex interactions between Mediterranean coastal areas. Future detailed studies of a highly heterogeneous historical biogeography and eco- these ‘natural island microcosms’ could greatly improve logical processes related to diverse island conditions. our knowledge of the functional and evolutionary processes Furthermore, most of the ups and downs of this biodiver- induced by rapid environmental changes in this region. sity were closely linked with human pressures which have changed many times through the long socio-ecological Keywords Coastal ecosystems Á Human impacts Á Insular history of these island landscapes since the Neolithic per- biogeography Á Land use changes Á Mediterranean region Á iod. At present, insular plant biodiversity and rural land- Sea-level rise scapes are threatened by diverse global environmental changes related to urbanization, habitat fragmentation, unsustainable tourism and other practices (e.g. overgrazing, Introduction forest fires), and by other more recent drivers such as climate warming and aridification, sea-level rise and biolog- The complex historical biogeography and the profound ical invasions. Some of these impacts will be exacerbated environmental heterogeneity explain the high diversity of on islands because of no (or highly limited) adjacent areas landscapes and vegetation types on islands of the of expansion, notably on the smallest ones (i.e. size \ ca. Mediterranean basin, one of the 35 terrestrial biodiversity 1000 ha). With regards to the biome crisis facing the hot spots of the world (Me´dail and Myers 2004). The Mediterranean basin and induced by human activities, associated high levels of biodiversity and ecological com- islands constitute key ecological systems and ‘current plexity have favoured the emergence of functional uniqueness for several ecosystems and plant communities that occur nowhere else. With about 10,000 islands and Editor: Erica Smithwick. islets (ca. 250 regularly inhabited by humans), the Electronic supplementary material The online version of this Mediterranean Sea represents one of the regions of the article (doi:10.1007/s10113-017-1123-7) contains supplementary world with the most islands and archipelagos. Its islands material, which is available to authorized users. contain a significant component of Mediterranean biodi- & Fre´de´ric Me´dail versity, notably a number of range-restricted species and [email protected] peculiar vegetation types (e.g. Vogiatzakis et al. 2008; Me´dail 2013, 2017). Past geographical and climatic chan- 1 Institut me´diterraneén de biodiversite´ et d’ećologie marine et ges, combined with current environmental heterogeneities, continentale (IMBE), Aix Marseille University/CNRS/IRD/ AU. Campus Aix, Technopoˆle de l’Environnement Arbois- have moulded unusually high levels of biodiversity and Me´diterraneé, 13545 Aix-en-Provence cedex 4, France biogeographical complexity. The diversity of ecosystems 123 1776 F. Me´dail of Mediterranean islands is also linked to the long-lasting The existence of endemic or range-limited plant species influence of humans as ‘designers’ of landscapes, who have can determine specific patterns of insular vegetation types shaped vegetation dynamics through burning, cutting, and landscapes. On large islands, plant endemism ranges grazing and ploughing (Blondel 2008). More recently, the from 8 to 17%, whereas the total number of taxa is greater biodiversity and functioning of these ecosystems were than expected, usually between 1600 and 2800 species and threatened by global environmental change, notably eco- subspecies (Table 2). In mountain ranges of islands, the logical footprint due to human expansion, climatic and sea- level of endemism is higher: above 1700 m a.s.l. endemics level changes, and biological invasions. represent 35–40% of the vascular flora in Corsica and in Crete. Each island has its own specificities of vegetation even if major physiognomic structures may appear similar The diversity of Mediterranean islands from one island to another. They are mostly covered by typical vegetations of the thermo-mediterranean and meso- Mediterranean islands are a kaleidoscope of environmental mediterranean belts, whereas the upper vegetation levels and biotic conditions (Me´dail 2017). This is due to the are restricted to the summits of the largest islands, notably wide range of sizes (from the largest island of Sicily cov- Corsica, Sicily, Crete and Cyprus. ering 25,700 km2 to small islets a few dozen square metres in size), in altitude (from Mt. Etna, 3342 m a.s.l. to flat islets only one metre a.s.l) and in remoteness, all of which Biogeography of Mediterranean islands, museum represent key parameters in island biogeography. There are and cradle of plant diversity a total of 157 large islands exceeding 10 km2 (1000 ha) in size, of which 86 (55%) are located in Greece (Me´dail The history of the Mediterranean basin setting is highly 2017). Forty nine islands cover more than 100 km2,of complex both from a geologic and a climatic point of view which 36 cover more than 200 km2. Small islands with a (e.g. Woodward 2009; Fig. 2). Tectonic events and the surface area less than 10 km2 are the most common, and Messinian salinity crisis—which induced an almost com- there are several thousands of such islands. Most islands plete desiccation of the Mediterranean Sea between 5.96 belong to the Greek archipelago with ca. 7600 islands and million years (Ma) and 5.33 Ma (CIESM 2008) (Fig. 2c)— islets in the Aegean Sea, more than 90% of which cover have strongly influenced the palaeogeography of the less than 10 km2 (Triantis and Mylonas 2009), and ca. 300 region, and thus the biogeographical history. If some pre- islands and islets in the Ionian Sea. Croatia is the second Mediterranean plant taxa exist since the Eocene (ca. country in terms of the number of islands (n = 1246), 40 Ma: Fig. 2a), the main diversification of the Mediter- whose 79 islands of more than 1 km2 and 653 small islands ranean species took place during (1) the Miocene (Fig. 2b), and islets have vascular vegetation (Nikolic´ et al. 2008). notably in conjunction with the collision of the African and Nearly all Mediterranean island ecosystems are under Eurasian plates with the Arabian plate and (2) the Pliocene the influence of the Mediterranean climate (Fig. 1), except with the onset of the Mediterranean climate (Fig. 2d). some parts of the high mountains of Corsica that contain Recurrent episodes of species dispersal and vicariance have subalpine and alpine vegetation belts with euro-siberian occurred between the eastern and western Mediterranean and even arctic-alpine plants (Gamisans 1999). The insular regions in relation to the several marine regressions or vegetation types usually considered as ‘typically Mediter- transgressions and the ongoing rise of Alpine and Atlas ranean’ are the evergreen and sclerophyllous shrublands orogenesis (e.g. Mansion et al. 2008). and forests under semi-arid (400 \ P = annual rain- The majority of Mediterranean islands are ‘continental falls \ 600 mm) or sub-humid (600 \ P = annual rain- islands’ sensu lato (including continental shelf and conti- falls \ 800 mm) bioclimates, corresponding to thermo- nental fragments according to Whittaker and Fernańdez- mediterranean and meso-mediterranean vegetation belts Palacios 2007), i.e. they were once part of the continent (Table suppl.); Fig. 1). If deciduous trees were the before their separation and drifting (such as the small cornerstones of ecosystem dynamics during the post-glacial continental sub-plate of Corsica-Sardinia which separated period, notably in the northern Mediterranean, these forests during

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