Bioclimate and reproductive potential at the cold limit of European deciduous tree species

Abstract

This thesis assessed factors that contribute to the explantion of the upper elevational and latitudinal limits of European broad-leaved tree species by using a set of ecological analysis, including in situ temperature measurements, a transplant experiment and a survey of the reproductive cycle and demography at the species limits. The following key questions were answered in five chapters: Do the elevational thermal limits of broad-leaved tree species correspond to their latitudinal thermal limits? Can we use temperature data from weather stations to predict temperature at broad-leaved tree species limits? Which facet of temperature at which phenological stage explain the most the elevational and latitudinal cold limits of broad-leaved tree species? Does seed quality restrict the reproduction of species at high elevation? Do the elevational limits of juvenile trees match with the respective adult tree limits or do the results offer an indication for recent species upward shift? Studied species & study region Ten broad-leaved tree species were selected for this thesis: Acer pseudoplatanus L., Fagus sylvatica L., Fraxinus excelsior L., Laburnum alpinum Mill.) Bercht. & J. Presl, Prunus avium L., Quercus petraea (Matt.) Liebl.,Sorbus aria L., Tilia platyphyllos Scop., Sorbus auccuparia L. and Ilex aquifolium L. The choice of species was driven by the aim of drawing conclusions beyond species level and beyond the regional focus. Thus, the selected species have a wide European distributional range and a wide elevational range in common. At the same time they cover a broad spectrum of plant families, namely Rosaceae, Fagaceae, Aceraceae, Oleaceae, Tiliaceae, Aquifoliaceae and Fabaceae. The studies were carried out in three distinct regions: In the Western Swiss Alps near Martigny (46°6'N, 7°4'E), in the Eastern Swiss Alps near Chur (46°51'N, 9°32'E) and in the South of Sweden (from 57°42' to 59°39'N, ca. 12°E). Both regions in Switzerland were selected because most broad-leaved tree species studied here, find their elevational limit in these regions and reach their highest positions in Switzerland. Furthermore, the large and steep elevational gradients found in these regions facilitated surveys, specimen collections and common garden experiments. In southern Sweden we studied species at their latitudinal limits, allowing a large-scale comparison. Comparisons of the elevational and latitudinal upper limits of broad-leaved tree species Christophe F. Randin, Jens Paulsen, Yann Vitasse, Chris Kollas, Thomas Wohlgemuth, Niklaus E. Zimmermann and Christian Korner We compared temperatures at the upper elevational and latitudinal limits of 18 deciduous tree species respectively in Switzerland and North of Europe, and hypothesized that species exhibit the same position (relative to the treeline) along the elevational and latitudinal gradients, which can be expected if species have reached their thermal cold limit at both high latitude and high elevation. We developed a method to identify a least-biased…