Browsing by Subject "Mikroilmasto"
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(2022)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.
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(2023)Microclimate research is an important part of research about our warming earth. Microclimate refers to a local climate that is partially independent of the free atmosphere formed in an area of a few square meters to a few square kilometers. In this study, the level of consideration of the microclimate is the air layer in the immediate vicinity of the earth's surface. Microclimates are characterized by air temperature, air humidity, timing of the seasons, and the variety of organisms that thrive in the area, which differ from the wider climate. Local microclimates arise from the interaction of atmospheric processes and environmental factors in the area. The thesis examines how the extreme temperatures of microclimates vary in different vegetation zones in Finland. Two research areas are located in the tundra vegetation zone in the northern parts of Finland, and the remaining five research areas are in the boreal vegetation zone. The research questions are: 1) How do the extreme temperatures (minimum and maximum temperatures) of the warmest month of the growing season, July, vary in the study areas? 2) Which environmental factors affect the extreme temperatures of the research areas? Environmental factors to be considered are ground level above sea level, relative ground level, slope, distance to the nearest bodies of water, canopy cover, solar radiation and windiness. According to the results, the minimum temperatures were statistically significantly affected by the canopy coverage mainly negatively, the absolute ground level mainly negatively and the slope, with the trend varying between negative, positive and unimodal depending on the study area. The environmental factors that had the greatest influence on the maximum temperatures were the absolute ground level, negatively in the south and positively in the north, the canopy coverage mostly negatively, and the relative ground level mostly positively. The research results were largely in line with the hypotheses. In the south, abundant forest vegetation lowered the maximum temperatures of forest environments and raised the minimum temperatures. In central Finland, in the study area covered by wetlands, lakes and fragmented forests, especially the distance to water bodies affected the extreme temperatures. In northern Finland, the tundra vegetation led to the strongest temperature fluctuations. The maximum temperatures of the research areas varied less than the minimum temperatures. The maximum temperatures in July remained between 21.3 and 31.7˚C degrees, the range was 10.4˚C. The minimum temperatures remained between -3.3 and 5.2 ˚C degrees, the range was 8.5 ˚C degrees. In the future, microclimate-related research in the Nordic countries could focus even more precisely on the interannual variations of micro-level temperature observations over a longer period of time, as well as on the specification of the characteristics that affect the temperatures in different vegetation zones.
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