The establishment of non-native plant species in relation to climate and land use in Britain

Human transport of species around Earth has led to the intentional and accidental introduction of many species into new regions. Introduced species can have significant impacts outside their native ranges, with a range of positive and negative ecological effects on native biota, community productivity and nutrient cycling. Climate and land use are major determinants of non-native species distributions, with climate setting the broad limits to plant distribution and productivity, and with human activity associated with different land uses affecting the dispersal and success of introduced species. There is potential for future changes in land use and climate to have an impact on distributions of non-native species, due to possible changes to transport, establishment and spread. This thesis uses records of plant species in Britain to determine patterns of non-native species richness with climate and land use, predict possible changes with climate change, quantify establishment of non-native species and to examine levels of establishment for groups of non-native species with different traits (Plant Functional Types). Models were used to examine the relationship between species richness of non-natives and natives with climate variables and land cover types, and projected climate data was used to predict possible future changes. An establishment index was calculated to quantify establishment of non-native species; it was found that date of introduction and range size are not necessarily good predictors of level of establishment and that well established species are less likely to be associated with urban areas than poorly established species. Distributions and establishment of Plant Functional Types were examined, showing that some groups have distinct patterns with land cover related to where they are most likely to be introduced. The least established groups show greater associations with land cover than with climate. Climate and land use changes have the potential to allow new species to establish and to allow already established species to spread due to shifts or expansions in their potential climatic ranges. Future studies of non-native species should attempt to distinguish between time since arrival and the level of establishment because the two may not be associated.