| Summary: | Icelandic plant communities are shaped by climate, volcanism and, since human settlement around 870 CE, by land use. Post-settlement vegetation changes in the lowlands have received more attention than in the highlands. Via palynological analyses of two peat profiles, this study examines highland vegetation change in north-west Iceland, and the role of abiotic and biotic factors, over the last two millennia. Core chronologies rely on tephrochronology and radiocarbon dating. A novel approach in this study is the use of general linear models (GLM) and general linear autoregressive moving average models (GLARMA) to examine the roles of environmental factors (landscape (in)stability, tephra deposition, temperature, grazing and plant interactions) in past plant community changes. Relative to lowland conditions, Betula pubescens was rare within the area from before settlement into the middle ages, while Salix and Betula nana were prominent. Deciduous woody plants became more abundant ca 1350-1700 CE but they generally declined with time while Ericaceae and Poaceae importance increased. Grazing, temperature change and tephra deposition were all important envirormental factors. Landscape instability explained spore abundance well, perhaps due to reworking of spores via soil erosion. Signs of plant interactions, especially competitive exclusion of other plants by deciduous woody plants and Poaceae, were prominent. Empetrum nigrum may have been involved in both positive and negative interactions, despite its possible allelopathic effects. Negative relationships between Cyperaceae and other plants may have arisen from wetland hydrology changes. No single biotic or abiotic factor was found to dominate vegetation change over the last two millennia. Frá landnámi hafa landnýting, loftslag og eldvirkni mótað íslensk gróðursamfélög. Gróðursaga láglendis er mun betur þekkt en saga gróðurs á hálendinu. Hér er rannsökuð gróðursaga síðustu tveggja árþúsunda á hálendi á norð-vesturlandi, með frjógreiningu sýna úr tveimur ...
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