The rich sides of mountain summits – a pan‐European view on aspect preferences of alpine plants
Authors: Winkler Manuela , Lamprecht Andrea , Steinbauer Klaus , Hülber Karl , Theurillat Jean‐Paul , Breiner Frank , Choler Philippe , Ertl Siegrun , Gutiérrez Girón Alba , Rossi Graziano , Vittoz Pascal , Akhalkatsi Maia , Bay Christian , Benito Alonso José‐Luis , Bergström Tomas , Carranza Maria Laura , Corcket Emmanuel , Dick Jan , Erschbamer Brigitta , Fernández Calzado Rosa , Fosaa Anna Maria , Gavilán Rosario G. , Ghosn Dany , Gigauri Khatuna , Huber Doris , Kanka Robert , Kazakis George , Klipp Martin , Kollar Jozef , Kudernatsch Thomas , Larsson Per , Mallaun Martin , Michelsen Ottar , Moiseev Pavel , Moiseev Dmitry , Molau Ulf , Molero Mesa Joaquín , Morra di Cella Umberto , Nagy Laszlo , Petey Martina , Pușcaș Mihai , Rixen Christian , Stanisci Angela , Suen Michael , Syverhuset Anne O. , Tomaselli Marcello , Unterluggauer Peter , Ursu Tudor , Villar Luis , Gottfried Michael , Pauli Harald 
Published: August 2016

Aim

In the alpine life zone, plant diversity is strongly determined by local topography and microclimate. We assessed the extent to which aspect and its relatedness to temperature affect plant species diversity, and the colonization and disappearance of species on alpine summits on a pan‐European scale.

Location

Mountain summits in Europe's alpine life zone.

Methods

Vascular plant species and their percentage cover were recorded in permanent plots in each cardinal direction on 123 summits in 32 regions across Europe. For a subset from 17 regions, resurvey data and 6‐year soil temperature series were available. Differences in temperature sum and Shannon index as well as species richness, colonization and disappearance of species among cardinal directions were analysed using linear mixed‐effects and generalised mixed‐effects models, respectively.

Results

Temperature sums were higher in east‐ and south‐facing aspects than in the north‐facing ones, while the west‐facing ones were intermediate; differences were smallest in northern Europe. The patterns of temperature sums among aspects were consistent among years. In temperate regions, thermal differences were reflected by plant diversity, whereas this relationship was weaker or absent on Mediterranean and boreal mountains. Colonization of species was positively related to temperature on Mediterranean and temperate mountains, whereas disappearance of species was not related to temperature.

Main conclusions

Thermal differences caused by solar radiation determine plant species diversity on temperate mountains. Advantages for plants on eastern slopes may result from the combined effects of a longer diurnal period of radiation due to convection cloud effects in the afternoon and the sheltered position against the prevailing westerly winds. In northern Europe, long summer days and low sun angles can even out differences among aspects. On Mediterranean summits, summer drought may limit species numbers on the warmer slopes. Warmer aspects support a higher number of colonization events. Hence, aspect can be a principal determinant of the pace of climate‐induced migration processes.