Browsing by Author "Aalto, Aino"

The ongoing environmental change will cause changes in arctic-alpine environment affecting both abiotic and biotic processes and the distribution of arctic-alpine vegetation that has adapted to the cold environment. Former studies on the distribution of arctic-alpine vegetation have been conducted more from a macroclimatic point of view neglecting the microclimate perspective. Microclimate refers to radiation, temperature, humidity, and wind conditions near the Earth’s surface. These conditions vary notably in the topographically heterogenous mountain tundra. The effect of the microclimatic factors is particularly important when investigating low-growing arctic-alpine vegetation as the microclimatic variables can be expected to describe the climatic conditions of the biotically active layer better than the macroclimatic variables. The purpose of this thesis is to study how the microclimatic conditions vary across different biotopes within mountain tundra and to examine which microclimatic variables best explain the local distribution of the arctic-alpine vegetation. The microclimatic variation in the different biotopes of the mountain tundra was studied by examining the statistical key figures of air and soil temperature and soil moisture measurements. Species distributions modelling was used to examine the distribution of arctic-alpine vascular plants and species correspondence to the microclimate variables as well as the importance of those variables on the species distributions. The research material consists of the microclimate and species data collected on the field as well as data based on topography and remote sensing. The data for the study were collected around Rastigaisa mountain in northern Norway. The explanatory variables used in the species distribution modelling included freezing degree day (FDD), growing degree day, radiation, soil moisture, topographic position index and information on the snow cover persistence. Species distribution modelling was performed using generalized boosted regression. From the modelling results the relative importance of the predictor variables as well as the predicted distributions of the species were interpreted. Microclimate factors varied between biotopes. The biggest variation in air temperature was observed at mountain tundra heath. Soil moisture had a levelling effect on the minimum temperatures and the FDD’s. The species distribution modelling results show that snow and moisture variable have a significant impact on the distribution of the arctic-alpine vegetation. Snow controls both temperature and moisture conditions and hence affects the stress that vegetation undergoes as well as the supply of nutrients.