| Summary: | This thesis examines the causes and consequences of vegetation change in the British countryside using landscape-scale survey data. The main data source is the Countryside Survey (CS) of Great Britain, augmented by an urban riparian survey in one chapter. Plant traits are used as response and explanatory variables and other datasets that track potential drivers of change were included in analyses. Vegetation changes observed in CS included loss of species richness in many habitats, increases in non-native species, eutrophication in upland and lowland habitats and a successional signal along linear features. Non-native species were less abundant than expected. Impacts on species richness from non-native cover were shown. Using trait data to indicate community characteristics, non-natives were found in disturbed conditions, (more forbs, annuals, higher fertility, pH and SLA). However, non-natives were also found in later successional communities dominated by individual non-natives. Native invasives are found in greater abundance than non-natives in the British Countryside. The effects of pre-conditioning by disturbance (or lack of management), increased nutrient availability and the influence of propagule pressure were tested and found to be significant for invasive species distribution. Nitrogen deposition was related to the presence of atypical nutrient-demanding species in upland infertile habitats whilst agricultural disturbance was associated positively with the density of atypical species. Nitrogen deposition was also shown to be associated with a loss of species richness and invasion and dominance by some species. The mechanism for species loss (eutrophication or acidification) varied by habitat type. There were also climatic effects; warmer temperatures were related to the invasion and expansion of invasive species and to overall species richness. This thesis used a hypothesis-led approach to study changes in the distribution of plant species and determine potential causes of change. This has led to new insights into how and why British vegetation is changing.
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