Browsing by Author "Juselius, Teemu"

Nowadays a greater number of people live in cities than in earlier times. In Finland, the portion of urban dwellers has nearly doubled in last 50 years. The urbanization has had undisputable benefits for mankind but it has also had widespread negative effects on nature. As cities grow natural habitats are replaced by spreading infrastructure. Remaining mires, forests and other natural habitats are smaller and more isolated than their rural counterparts. These urban habitats are affected by increased pollution and nutrient loads, trampling and other detrimental effects caused by human activity. Alien invasive species may also spread into indigenous vegetation and more of these areas are affected by edge-effects. Ombrotrophic bogs are one of the most nutrient-poor habitats in the North and receive nutrients only by dry and wet deposition. They have been reported to suffer from increased nutrient deposition. Hydrology also has a vital part in function and form of ombrotrophic bogs. Spread of urban infrastructure may alter the way bogs receive water due to increased sealed surface in the catchment areas of these bogs. The effects of urbanization on ombrotrophic bogs in Finland has not been studied previously and the aim of this Master’s thesis is to examine the differences between vegetation in urban and rural bogs and the effects of the size of bog area, nearby population and total N content of surface peat on bog vegetation in different bog types: dwarf shrub pine bogs, low sedge bogs, Sphagnum fuscum pine bog and Sphagnum fuscum bog. Last two were studied together due to their similarities. According to this study the differences between urban and rural bogs in Southern Finland are small. The greatest differences were observed among dwarf shrubs typical for bogs but the effects varied between bog types. In dwarf shrub pine bogs, the amount of dwarf shrubs decreased while in low sedge bogs, the cover of Vaccinium oxyccocos, and in Sphagnum bogs, the occurrence of Empetrum nigrum increased. The bogs studied in urban sites were generally smaller and more isolated than rural bogs. Around urban bogs, there were also significantly higher number of residents than in rural areas, and one of the most distinct effects of urbanization on bog vegetation discovered was reduction of cover and appearance of species vulnerable to trampling. The increased nutrient loads usually reported in urban habitats was not visible in nitrogen content of surface peat. On the contrary, low sedge bogs seemed to have higher nitrogen content on rural bogs, which may be caused by intense agriculture in rural areas. The reason for not detecting increased urban nitrogen deposition based on peat samples may be caused by increased nitrogen uptake of Sphagnum mosses. Sphagnum mosses have been reported to benefit from increased nitrogen deposition until they reach nitrogen saturation point. After this the excess nitrogen enters peat soil. Low nitrogen deposits in Southern Finland can probably be used fully by Spaghnum mosses and thus no increase in nitrogen content was observed. The results of this study indicate that ombrotrophic peat bogs are at least partly resistant to the effects of urbanization. The level of urbanization in Finland is lower than in Central Europe, which may lead to lowered levels of detrimental effects caused by urbanization. Alien species are probably also unable to invade the acidic and nutrient poor urban bogs. The mire types studied here are also usually situated in the centre of ombrotrophic bogs and may have avoided most of the edge effects. However, if studied, the edges of the urban bogs might have shown large number of harmful effects caused by urbanization.