Browsing by Subject "maksimilämpötila"

Climate change is going to bring a change for ecosystems and their abiotic and biotic processes. Relationship between climate and ecosystems is usually studied using macroclimatic data, but plants have been found to be more closely associated with changes in microclimates. Microclimates involve temperature, wind, radiation, and humidity conditions near the ground surface. Microclimates can change over short distances creating differences for areas general climatic conditions. Microclimates can help plants to survive in the edge of their dispersal area or create stronger variations in temperatures. Not much research conducted on microclimates in boreal ecosystems yet. The aim of this thesis is to illustrate how environmental variables affect temperatures in different seasons inside boreal biome. Microclimates are a combination of physical processes and environmental variables. Main physical processes are energy released and bound by changes in the state of water, heat flux between soil and air, and radiation balance. Environmental variables are key components on defining how physical processes occur in the area affecting the microclimatic temperatures. Topography creates change in the lapse rates via altitude variations, and slope curves and orientation change radiation and moisture conditions. Radiation and moisture conditions also vary according to the vegetation factors, for example in the forest where canopy cover and vegetation height create differences in physical processes. Water masses and mires affect the area’s moisture conditions and heat flux between air and water. Heat flux between air and soil on the other hand is affected by quality of soil and wind conditions. Wind currents affect the mixing of different layers of air and the cold air pooling together with local topography. Relative influence of the environmental variables was studied using 8 study areas located in different boreal climatic zones. Study sites included 50 to 100 temperature meters, covering different environmental conditions in the area. Temperature data were collected at a height of 15 cm above the ground over a two-year period. In this thesis explanatory variables where canopy cover, radiation, slope, wind, distance to forest edge, TWI, and water and wetland portions. GAM-models were generated for different temperature variables for different months and years. Explanation ability of the model was evaluated with bootstrap-method. Relative influence of the explanatory variables was examined by variable randomization. Models explanatory power was highest in the southern study areas and decreased slightly when moving to the northern sites. There was a positive correlation between model explanatory power and its stability. Based on this the results are more reliable in the southern sites and during the summer. Temperatures observed in microclimates followed the changes in the macroclimatic conditions. In the northern areas, the main environmental factors explaining temperature variations were mainly topographic variables such as slope, wind, and TWI. In the southern areas vegetation variables like canopy cover, distance to forest edge and wetland portion were more relevant in explaining the temperature variations. Results also suggest that topography driven wind conditions are an important variable in the northern areas. Wind was found to decrease temperatures in winter months and increase temperatures in summer. The influence of wind has not yet been taken into consideration in many previous studies, as it is affected by several different factors. Further research into the factors affecting microclimatic temperatures is important in order to determine more precisely the differences between the environmental factors influencing the temperatures and their relative significance in different years. However, the temperature variables occurring in the boreal zone can be explained by examining the topographic and vegetation variables.