New farming needs and innovations have, over time, led to changes in land use. Arable fields have been turned into pastures and semi-natural pastures into arable fields. Due to the ecological value of continually grazed semi-natural pastures in Sweden the aim of this study is to find out how former arable fields that are permanently grazed differ from semi-natural pastures. In this study I selected appropriate semi-natural pastures from a national monitoring program on seminatural- pastures and meadows. Plots continuously grazed were compared with grazed plots on former arable fields. Pair-wise differences in the Ellenberg indicator values Light (L), Soil moisture (F), soil pH (R) and soil nitrogen (N), vertical coverage of trees, bushes and vegetation, species richness and species composition were tested. Except for species composition there were only small differences between former arable fields that are permanently grazed and semi-natural pastures. That means former arable fields can with time and grazing gain many of the values continuously grazed semi-natural pastures have.

The research contained in these papers embodies both results from direct archaeological investigation and also the development of techniques (geophysical, chronological and geoarchaeological) in order to understand long-term settlements and their associated landscapes in Orkney and Shetland. Central to this research has been the study of soil management strategies of arable plots surrounding settlements from the Neolithic to the Iron Age. It is argued that this arable system provides higher yields in marginal locations. The ability to enhance yield in good years and to store surplus can mitigate against shortage. Control and storage of this surplus is seen as one catalyst for the economic power of elite groups over their underlying or ¿client¿ population. The emergence of a social elite in the Iron Age, building brochs and other substantial roundhouses of near broch proportions, is seen as being linked to the control of resources. Evidence at the site of Old Scatness indicated that there was a continuity of wealth and power from the Middle Iron Age through the Pictish period, before the appearance of the Vikings produced a break in the archaeological record. The Viking period saw a break in building traditions, the introduction of new artefacts and changes in farming and fishing strategies. Each of the papers represents a contribution that builds on these themes.

The research contained in these papers embodies both results from direct archaeological investigation and also the development of techniques (geophysical, chronological and geoarchaeological) in order to understand long-term settlements and their associated landscapes in Orkney and Shetland. Central to this research has been the study of soil management strategies of arable plots surrounding settlements from the Neolithic to the Iron Age. It is argued that this arable system provides higher yields in marginal locations. The ability to enhance yield in good years and to store surplus can mitigate against shortage. Control and storage of this surplus is seen as one catalyst for the economic power of elite groups over their underlying or 'client' population. The emergence of a social elite in the Iron Age, building brochs and other substantial roundhouses of near broch proportions, is seen as being linked to the control of resources. Evidence at the site of Old Scatness indicated that there was a continuity of wealth and power from the Middle Iron Age through the Pictish period, before the appearance of the Vikings produced a break in the archaeological record. The Viking period saw a break in building traditions, the introduction of new artefacts and changes in farming and fishing strategies. Each of the papers represents a contribution that builds on these themes.

1. Seed bank and seed rain represent dispersal in time and space. They can be important sources of diversity in the rural landscape, where fragmented habitats are linked by their histories. 2. Seed bank, seed rain and above-ground vegetation were sampled in four habitat types (abandoned semi-natural grassland (ABA), grazed former arable field (FAF), mid-field islet (MFI) and grazed semi-natural grassland (SNG)) in a rural landscape in southern Sweden, to examine whether community patterns can be distinguished at large spatial scales and whether seed bank and seed rain are best explained by current, past or intended future vegetation communities. 3. We counted 54 357 seedlings of 188 species from 1190 seed bank and 797 seed rain samples. Seed bank, seed rain and above-ground vegetation communities differed according to habitat. Several species characteristic of managed grassland vegetation were present in the seed bank, seed rain and vegetation of the other habitats. 4. The seed banks of SNGs and the seed rain of the FAFs were generally better predicted by the surrounding above-ground vegetation than were the other habitat types. The seed rain of the grazed communities was most similar to the vegetation in the FAFs, while the seed banks of the abandoned grasslands most resembled the vegetation in SNGs. 5. Gap availability and seed input could be limiting the colonisation of target species in FAFs, while remnant populations in the seed bank and the presence of grassland specialists in the above-ground vegetation indicate that abandoned grasslands and mid-field islets could be valuable sources of future diversity in the landscape after restoration. 6. Synthesis and applications. SNG communities are able to form seed banks which survive land-use change, but their seed rain does not reflect their above-ground communities. It is important that grassland plants set seed. By connecting existing grasslands with restoration targets, increased disturbance in the target habitats would allow for colonisation via the seed bank or seed rain, while decreased grazing intensity would benefit seed production in the source grasslands. Otherwise, landscape-wide propagule availability might increase with a more varied timing and intensity of management.

Species assembly into local communities from the surrounding region can be caused either by species failure to reach the site (i.e. seed limitation) or to establish (i.e. establishment limitation). The aim of this thesis was to investigate plant species assembly and to determine the relative importance of different factors in that process. In a cultivated landscape in southeast Sweden, plant community assembly was studied in grazed ex-arable fields. Community assembly from the surrounding region into the local community was explored using trait-based null models and seed sowing and transplanting experiments. The influence of local environmental factors and landscape history and structure on community assembly was also studied. In addition, differences in species assembly between ex-arable fields and semi-natural grasslands were explored. Seed limitation was the strongest filter on local community assembly. Only a fraction (36%) of species in a region dispersed to a local site and adding seeds/transplants increased species establishment. Species abundance at the regional scale, species dispersal method and seed mass strongly influenced which species arrived at the local sites. Establishment limitation also affected the assembly. Of species arriving at a site 78% did establish, seedling survival was low and which species established was influenced by species interactions, local environmental conditions and stochastic events. In addition, landscape structure that determined the species richness in the regional species pool influenced the local assembly. The comparison between assembly in ex-arable fields and semi-natural grasslands indicated that the main cause of difference in species assembly between them was difference in their age. The main conclusion of this thesis is that regional processes are more important than local factors in determining plant community assembly. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.</p>