| Summary: | For most of the Holocene the main driver of vegetation and environmental change in Iceland was climate, although intermittent volcanic events had short term impacts. This changed with the Norse colonisation in the late 9th century AD, from when land use became a dominant force in terrestrial ecosystem development. This thesis presents a regional vegetation and environmental reconstruction from Northwest Iceland, based on data from three lake sediment cores and one peat core. The aim of the study was to examine the sensitivity of the Icelandic terrestrial ecosystem to external forcing mechanisms i.e. climate, tephra deposition and land use. The study sites form a transect from the coast on northern Skagi peninsula, through the lowland to the highland margin. The reconstructions reveal that vegetation changes were asynchronous between sites as a result of their different environmental settings. Vegetation changes in the lowland were primarily driven by climate. Based on pollen data the warmest periods of the Holocene were c. 10,100-8700 and 8000-6000 cal. yr BP and the optimum period for Betula pubescens woodland was c. 8000-6000 cal. yr BP. Cooling climate led to a woodland decline after c. 6000 cal. yr BP. Vegetation succession in the early Holocene was slower at the highland margin than in the lowland. Open woodland developed c. 7800 cal. yr BP and persisted until c. 4200 cal. yr BP. The woodland was probably at its ecological limit for most of that time. Human settlement began to influence the environment at the highland margin c. 1000 cal. yr BP, marked by changes in vegetation and increased environmental instability. Birch woodland is not observed in the record from the coast, probably due to oceanic influences. Dwarf shrub heath probably endured there throughout the Holocene. Examination of the influence of the Hekla 4 tephra (c. 4200 cal. yr BP) on vegetation revealed that the tephra had an impact on both relatively stable open woodland in the lowland and open woodland under pressure at the highland ...
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