Impacts on plant communities by elevated CO2 concentration

Sammanfattning: Our climate is in change. Carbon dioxide (CO2) levels this high, as the present CO2 concentration (≈370 ppm), have not been seen for the past 420 000 years. The cause for this is a combination of industrial CO2 emissions, the burning of fossil fuels and emissions arising from land use changes, such as deforestation and cultivation of virgin lands etc. An approach to this problem could be storage of CO2. Deep saline aquifers have the greatest storage potentials in the Nordic countries. Yet, it will probably take one or two decades before the technique for storage of CO2 will be applicable in a greater extent in Europe. A condition for storage of CO2 is to find storage places that guarantee that eventual leakage will have no essential significance in a time period of a couple of hundred years. The aim of this thesis is to find plant indicators on elevated CO2 concentration that could be used in detecting leakages of stored CO2. A comparison was done between plant communities near a CO2 spring in Italy that were exposed to elevated CO2 concentration and plant communities in a control area with ambient CO2 concentration regarding the percentage cover of vascular plants. Ellenberg indices of soil pH (R), light (L), soil moisture (F) and nitrogen content (N) were used to estimate and compare the environmental conditions and vegetation preferences of the two study areas. Shannon-Wiener- and evenness indices were calculated for the two study areas. Ordination method, Correspondence Analysis (CA), was used to illustrate differences, similarities and gradients in the collected data material. There were no significant differences between the CO2 area and control area regarding cover or Shannon-Wiener- and evenness indices. However, there were significant differences in Ellenberg indices for soil pH and nitrogen content between the CO2 and control area. The ordination showed a strong correlation with the first axis in the CA-diagram and the F, N and R-indices, consequently creating a gradient between them. Although some significant differences were found between the areas, the general conclusion is that no clear differences can be found between an area with elevated CO2 concentration and another with ambient CO2 concentration when looking at the vegetation composition alone.