Flora 207 (2012) 168–178 Contents lists available at SciVerse ScienceDirect Flora jo urnal homepage: www.elsevier.de/flora A biogeographic delineation of the European Alpine System based on a cluster analysis of Carex curvula-dominated grasslands a,∗ b Mihai Pus¸ cas¸ , Philippe Choler a A. Borza Botanical Garden, Babes¸ -Bolyai University, 400015 Cluj-Napoca, Romania b Laboratoire d’Ecologie Alpine UMR 5553 UJF-CNRS and Station Alpine J. Fourier UMS 3370 UJF-CNRS, Université de Grenoble, F-38041 Grenoble, France a r t i c l e i n f o a b s t r a c t Article history: Biogeographic delineations within the European temperate mountains remain poorly understood, as Received 28 June 2011 there has been little effort to assemble and analyze vegetation relevés covering Pyrenees, Alps, Carpathi- Accepted 4 October 2011 ans and Balkans altogether. Our study tackles this issue by focusing on the widely distributed alpine acidic grasslands dominated by Carex curvula. Cluster analysis of more than 800 vegetation relevés revealed the Keywords: European-scale spatial patterns of vascular plant diversity in these alpine grasslands. The geographical Alpine grasslands distribution of floristic clusters was partly congruent with the physiography of European mountains. Species richness Southern European ranges (Southern Balkans and Pyrenees) exhibit a high level of endemism and corre- Distribution patterns Phytogeography sponding floristic clusters are well separated from the others. Marked floristic similarities between the Endemism Easternmost Alps, the Carpathians, and the Northern Balkans (Stara Planina) supported a major floristic Indicator species boundary that runs through the Austrian Alps and that is likely the legacy of a shared Quaternary his- tory. Within the Alps, floristic clustering was mainly driven by ecological drivers and not geography. This paper presents the first detailed study of spatial patterns of species distribution within the European Alpine System, based on a comprehensive analysis of within- and between-community species diversity. It shows that the quantitative analysis of large and consistent data sets may question the traditional delineations of biogeographic regions within European mountains. © 2012 Elsevier GmbH. All rights reserved. Introduction patches (Kreft et al., 2008). Previous works have shown that spa- tial arrangement of these islands differs considerably among the Temperate mountains of Europe share a number of common various mountain ranges of the EAS (Pus¸ cas¸ et al., 2008b). This has features – flora, vegetation, fauna – that prompted biogeographers important consequences on species dispersal constraints and geo- to include Pyrenees, Alps, Carpathians and Northern Balkans into graphical ranges (Svenning and Skov, 2004). In addition, a number a same biogeographic region, the so-called European Alpine Sys- of phylogeographic studies have shown that the glaciations of the tem (EAS: Ozenda, 1985, 2009). The EAS is a well-known hotspot Quaternary period have had contrasting impacts on the alpine flora of plant diversity (Barthlott et al., 2007; EEA, 2005). At the regional of the EAS mountains (Comes and Kadereit, 2003; Kadereit et al., scale, steep environmental gradients produce complex patterns of 2004). For example, it is likely that only a few mountain ranges of diversity and high turnover in species composition across short dis- the EAS were significant refuges for alpine plants during ice ages tances (Barthlott et al., 2005; Körner, 2007). At the continental scale, and this is a key issue to understand the current spatial distribu- favorable habitats for mountain plants are separated by unfavor- tion of genetic diversity within these species (Schönswetter et al., able, lowland habitats, resulting in a highly fragmented distribution 2005; Tribsch, 2004). Most of these studies have focused on the of alpine vegetation and a high degree of endemism (Coldea et al., infra-specific level of diversity using a limited number of taxa (but 2009; Ozenda, 2009; Pauli et al., 2003; Pawłowski, 1970). Moun- see Alvarez et al., 2009). By contrast, there has been less effort to tains of the EAS are examples of sky islands system (Heald, 1951) examine how geography and post-glacial history have influenced that offer large opportunities to examine how history and ecology diversity patterns at the level of species assemblages, including have shaped species distribution. within- and between-community species diversity. Species diversity within and among islands of alpine habi- The mountain flora of Europe has been explored for more than tat is primarily controlled by the area and the isolation of the two centuries (e.g. Allioni, 1785; Baumgarten, 1816; de Lapeyrouse, 1818; Rochel, 1838; von Crantz, 1769). Biogeographers have early addressed floristic similarities and dissimilarities among the moun- ∗ tain ranges of the EAS (Braun-Blanquet, 1923, 1930; Gaussen and Corresponding author. Lerendde, 1949; Wołoszczak, 1895). Despite of a large number of E-mail address: [email protected] (M. Pus¸ cas¸ ). 0367-2530/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2012.01.002 M. Pus¸ cas¸ , P. Choler / Flora 207 (2012) 168–178 169 Fig. 1. (a) Distribution of Carex curvula subsp. curvula in the European temperate mountains (dark gray) and location of the grid cells (6 latitude and 10 longitude resolution) where vegetation relevés are available (white squares). Light gray is for the areas above 800 m. (b) The number of relevés available in each grid cell (gray circles) and the total number of relevés for each mountain range. local and regional studies (e.g. Lüth et al., 2011; mountain grass- characteristic plant communities of the higher European mountain lands of Eastern Alps), very few comparative analyses of alpine ranges, floristic data are available in a large number of regional plant communities have covered large areas of the whole EAS monographs. Moreover, these high-elevation grasslands have not (e.g. Horvat et al., 1974; but see Sibíkˇ et al., 2010, for subalpine been severely affected by land use and the current floristic diver- vegetation). However, most recent studies have put emphasis on sity patterns mostly reflect the outcome of long-term evolutionary the statistical analysis of vegetation relevés without performing a history (Grabherr et al., 2000). All these features make these grass- detailed analysis of spatial patterns of species distribution. Rather lands an excellent model to delineate biogeographic regions within ironically, the delineation of biogeographic regions within the the EAS. Based on clustering analysis of a very comprehensive syn- EAS remains poorly understood, especially because of the absence thesis of vegetation relevés, we addressed the following questions: of comparative floristic data between the different ranges. Only (1) what are the species diversity patterns of C. curvula-dominated recently, the detailed mapping of the flora of the Alps was linked grasslands in the mountain ranges of the EAS? (2) where are the with the species chorology inside the EAS (Aeschimann et al., 2004), main floristic boundaries located and do the biogeograhic regions but an overall analysis of the alpine plant species distribution in this correspond to natural entities (i.e. the mountain ranges)? and (3) range is still needed. what are the indicator species of each identified cluster? Latest advances in multivariate analysis and computational power now allow a more robust delineation of biogeographic Materials and methods regions based on quantitative analysis of large data sets (Kreft and Jetz, 2010). In this study, we addressed this issue by focusing on Vegetation data the alpine grasslands dominated by the sedge Carex curvula All. subsp. curvula, hereafter C. curvula. These alpine grasslands are Carex curvula is endemic to the EAS. It is the dominant species widely distributed in the EAS (Pus¸ cas¸ , 2005) where they repre- of extensive swards mainly occurring between ca. 2200 and sent the typical late-successional communities of the alpine belt 2700 m a.s.l. in the Pyrenees, the Alps, the Carpathians and the on acidic substrates (Choler and Michalet, 2002; Niederfriniger- mountains from Balkans (Stara Planina, Rila, Pirin) and the Dinar- Schlag and Erschbamer, 2000; Pus¸ cas¸ et al., 2008b). The very few ides (Fig. 1a, Pus¸ cas¸ , 2005). The plant communities dominated by C. curvula-dominated grasslands that were described in the Alps C. curvula were among the first to be described by European phy- on dolomites and shales (Erschbamer, 1992) have been shown to togeographers (the so-called “Curvuletum” of Brockmann-Jerosch, be dominated by introgressed forms between C. curvula All. subsp. 1907; Rübel, 1911), and the floristic composition of these alpine curvula and C. curvula All. subsp. rosae, an edaphically differentiated grasslands has been studied in the first surveys of the alpine vege- ecotype that occurs on base-rich substrates (Choler et al., 2004). tation of the Carpathians (Borza, 1934), the Balkans (Horvat et al., Because C. curvula-dominated alpine grasslands is one of the most 1937), and the Pyrenees (Braun-Blanquet, 1948). Since then, a large 170 M. Pus¸ cas¸ , P. Choler / Flora 207 (2012) 168–178 number of monographs have described floristic diversity of these algorithm allows the use of various distances. Our final results were grasslands in various regions of the EAS (see Appendix 1 for an not significantly different when other distance metrics (e.g. Sokal extended list). However, existing phytogeographic syntheses are and Michener, 1958) were used (data not shown). Exploratory anal- restricted to one mountain range only (Coldea, 1991; Pus¸ cas¸ et al., yses of the floristic data set were conducted using a varying number 2005; Roussakova, 2000; Theurillat, 1996). To our best knowledge, of prescribed groups (values of k ranging from 2 to 7). The number there has been no comprehensive analysis of these grasslands at of times a given relevé was assigned to a given cluster was com- the EAS scale. puted. A relevé was finally assigned to the cluster to which it was We assembled 853 relevés of alpine vegetation dominated by the most frequently associated.