| Summary: | The use of non-native tree species in forestry is both praised and questioned. Foresters have often promoted their use, mainly because of higher growth rates, resilience to pests and diseases and improved survival under harsh conditions. Nevertheless, non-native tree species can also have negative impact on biodiversity and ecosystem functioning, especially when introduced to former treeless vegetation. In this master thesis, I have used data from the Icelandic Forest Inventory to compare the differences in understory vegetation, berry production, game potential and esthetical value between the non-native tree species Pinus contorta and the native tree species Betula pubescens in Iceland. Species included in the analyse were: Empetrum nigrum, Carex vaginata, Geranium sylvaticum, Vaccinium uliginosum, Rubus saxatilis, Vaccinium myrtillus, Bistorta vivipara in addition to vegetation cover of bryophytes, fungi, lichen, pteridophytes and herbs. Data was divided into three age classes; young forest, middle age forest and old forest. The inventory plots covered the whole Iceland. My result showed that bryophyte cover was significantly higher in old stands of P. contorta compared to B. pubescens. Arguably this is linked to the more acidic soils and humid forest floor that P. contorta are associated with. The presence of Dryas octopetala, Vaccinium uliginosum and E. nigrum were higher in P. contorta stands than B. pubescens in middle age forest. The presence of D. octopetala was higher in older stands compared to young stands, regardless tree species, which probably is connected with sheep grazing in Iceland. D. octopetala is a highly palatable plant and the high presence of sheep in Iceland is probably reducing its range. Due to the common practise of fencing around plantations this probably favoured D. octopetala. In other words it is likely that the fencing of the plantations was the main reason for higher abundance in older forest, not the forest per se. In the middle age class there were a significantly higher ...
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