Thesis supervisor: Associate Professor Seni Arne Sellin and Seniro Research Fellow Margus Pensa, University of Tartu
Opponent: Carolina Martínez-Ruiz, PhD, University of Valladolid (Hispaania), Associate Professor
Oil shale mining has affected ~1% of the Estonian terrestrial area. Due to mining, natural landscapes in NE Estonia have been replaced by artificial landforms—mine spoils and waste piles. The first aim of this thesis was to describe the development of vegetation and soils in the Narva opencast mine and on Kohtla-Järve semicoke hills in different plantations and areas left to natural succession. According to the results of the thesis, plantations established in Narva mine can show remarkably good growth. Among ~30-year-old stands, alder and silver birch plantations are most productive. Natural stands develop slower, although at comparable rate to Scots pine plantations, which dominate the afforested area. Broadleaved species, especially alders, also seem to enhance soil development and herb layer productivity on both mine spoil and semicoke dumps. Species composition of herb layer differs significantly between site types on mine spoil and is most diverse in natural stands. Thus, vegetation and landscape in reclaimed opencasts could be diversified by planting different tree species and letting natural succession occur within plantations.
The second aim was to assess changes in bog ecosystems caused by alkaline air pollution from power plants and the lowering of the water table by forestry-drainage, peat mining and underground oil shale mining. Study was conducted in marginal areas of Kalina and Selisoo bogs. In both, but especially in Kalina, species composition has changed due to air pollution. In addition, both air pollution and drainage have contributed to the increase of tree growth and decrease of moss productivity. Lowering of the water table also leads to increased CO2 emissions from peat, originating from decomposition and root respiration. Our results suggest that average water table and/or stand volume, but not species composition, could serve as indicators of peat carbon fluxes for poorly-drained forested bogs although underlying relationships require further investigation.