Effects of climate change on alpine vegetation – functional analysis as a basis for future predictions

Despite broad evidence that climate change continuously effects alpine vegetation at different levels, the mechanistic understanding of these changes is still missing. The aims of the present thesis were elucidating three key aspects regarding the application of a functional approach to explore climate-induced changes of alpine vegetation. In the first part of the thesis, climate relevance of three key plant functional traits (specific leaf are (SLA), seed germination, pollen germination and pollen tube growth) was examined, in order to prove the possibility to use them as direct correlates of species distribution ranges. Second, I aimed to provide recommendations for correct application of the functional traits, considering trait intraspecific variability, trait variations at species and community levels, effect of other environmental factors on trait-climate relation and trait’ phylogenetic constraints. In the last part of the thesis the functional approach as suitable tool to detect mechanisms ruling recent changes of alpine vegetation was verified. Chapter 2 deals with the strength of the relationship between SLA and temperature at the population, species and community levels, including impacts of other environmental habitat characteristics on this relationship. The results of this chapter indicated that the intraspecific variability of SLA values was relatively low. Only 5 out of 28 studied species showed significant differences in their trait values along the temperature gradient. SLA was significantly correlated with temperature at the species (r²=0.04, p<0.001) and community levels (r²=0.08, p<0.001). The correlation between SLA and the mean annual temperature was modified by the effects of disturbance and soil phosphorous content, explaining 9.8% and 8.9% of the modelled variation, respectively (r²=0.89, p<0.001). We suggest that the strong relationship between SLA and temperature provides convincing evidence that this easy-measurable trait can be used as a predictor of species distribution ranges under changing temperature conditions. In chapter 3 I tested whether temperature requirements of pollen germination and tube growth could be used as direct correlates for predicting species distribution ranges. The results of this study revealed a strong and positive relationship between the minimal and optimal temperatures of pollen germination and temperature conditions at our collection sites (r²=0.41, p<0.01 and r²=0.2, p<0.05, respectively). For pollen tube growth, the minimal and optimal temperatures of the process were also significant predictors of species occurrence under the respective climatic conditions (r²=0.61, p<0.001 and r²=0.57, p<0.001, respectively). The strong relationship found between the temperature requirements of the progamic phase and habitat temperature could help in understanding the present species distribution along climatic gradients from a functional perspective and assist in better projecting of future distributional range alterations caused by environmental changes. Chapter 4 explores to which extent germination requirements of species with different geographic boundaries are related to their habitat macroclimatic characteristics. The results of the study show that initial temperature of seed germination (T ) is direct correlate for predicting species distribution ranges along temperature gradient. The study reveals that T is strongly negatively correlated to habitat temperature; among the studied species T clearly increased with decreasing mean annual temperature (MAT)(r²= 0.57, p<0.001). Considering phylogenetic biases, coevolution of seed traits as well as precipitation along with microclimatic factors did not affect the strength of this relationship. Our results suggest that the T -MAT relation can particularly provide insights into species distribution patterns, vegetation dynamics and community assembly rules along altitudinal and latitudinal gradients. We argue that including the T in species distribution models may help to improve the accuracy and specificity of predictions of vegetation shifts under global change scenarios. The chapter 5 deals with changes in subalpine, lower and upper alpine vegetation belts in the Bavarian Alps in last 50 years. In order to reveal mechanisms standing behind the changes, functional traits, along with several common floristic and phytosociological methods, were applied. The results of the study indicate that the direction and magnitude of the changes differed considerably among the studied communities and were dependent on initial species composition, vegetation structure and geographical context of individual vegetation belts. Although the species richness did not change significantly over last 50 years in the dense subalpine Seslerio-Caricetum sempervirentis communities, the immigration of species from lower altitudes and increased environmental favorability for already present thermophilous species led to increase of plant cover (+23%). The most pronounced changes were found in sparse low alpine Caricetum firmae communities. Due to gap availability and low competitive ability of alpine species, significant increase in species richness and plant cover (+6.4 species and +18%, respectively) were detected in this vegetation belt. The analysis revealed that in both communities species with traits that are advantageous under warmer conditions, such as higher specific leaf area, high stature and heavier seeds, significantly increased their frequencies and abundances. Floristic and vegetation changes of upper alpine communities were contrasting to those found in the study region as well as in the close mountain ridges. Despite temperature increase and available for colonization gaps in the communities, species richness (–4.7 species) and plant cover (–25%) significantly decreased. We argue that increased instability of high alpine habitats, due to upward retreat of the permafrost zone (as a consequence of recent warming), could hamper the colonization of high altitudes by montane and subalpine species, since they demand developed soils with high water-retention capacity. Finally, in chapter 6 we conclude that functional approach has a big potential to improve understanding of climate-induced vegetation changes at high altitudes and better predict the direction and magnitude of these changes under future climate scenarios. Some aspects of future studies in this field are also discussed.