Mountain Only 5% rises above the tree

Mountain ranges in Europe consist of a discontinuous system, forming isolated habitats for plant species (Körner, 2013). The Alps and the Carpathians are part of this discontinuous system, forming a mountain belt (Figure 1). The Alps cover an area of about 1,200 km long and 200 km wide with peaks rising above 4,000 m. Meadows and grasslands make up about 25% of the vegetation and forests cover over half of the Alps (Sundseth, 2009). The Carpathians are slightly longer (1,450 km), but twice as narrow as the Alps with peaks half as high. As a result, the land is mainly covered with trees. Only 5% rises above the tree line (Sundseth, 2009). Both mountains, especially the Alps, consist of a complex labyrinth of ranges divided by deep valleys and rivers (Sundseth, 2009). These ranges, valleys and rivers create isolated patches with high altitude.
It is well known that isolation by time and space is a driver for genetic differentiation and eventually speciation (Grivet & Petit., 2002; Hewitt, 2001; Linhart et al., 1981). This is illustrated by Körner (2013), he showed that alpine plants respond to mountain environments with a high degree of specialization (Körner, 2013). Areas across the Alps and Carpathians are isolated for millions of years (Handy et al., 2015) by deep valleys and rivers which are difficult to cross. This rises the question to what extent genetic differentiation within species occur across the Alps and Carpathians.
A particular interesting species to research is Juncus trifidus, also known as highland rush, a species from the Juncaceae (Rush) family. Sexual reproduction by flowering is dominant, but occasionally, asexual reproduction occurs. The habitat ranges from cliffs to meadows, dry to moist soil and sandy to gravelly substrates. The plant also occurs as pioneer on roadsides and ski slopes. Due to these characteristics, the species is widely spread across the world, native to Canada, United States, Iceland, Scandinavia, Europe and Asia. (Aiken et al., 2007) The wide distribution and pioneer properties suggest that the species adapts easily to different circumstances and is susceptible to differentiation.
The distribution of J. trifidus in the Alps and Carpathians (Figure 2) seems to correspond with the isolated habitats of high altitude across the mountain ranges. Based on this spatial isolation and the properties of J. trifidus, expected is that the species clusters in four different groups with a significantly different genome, illustrated by the different colors in Figure 2.