Plant population responses to environmental change and the role of biotic interactions along environmental gradients

Environmental conditions drive the occurrence and growth of plant populations as well as the structure and composition of plant communities. Plant responses to change in their environment are the net outcome of species-specific life histories, biotic interactions and habitat requirements. Recently global climate change has increased the need to understand the relative importance of these processes in predicting risks of extinction within existing communities and invasion by alien species. Changes in the extent and limits of a species range are a typical response to environmental change. Large-scale distribution shifts are the outcome of colonisation and extinction linked to the performance of plants in local populations. Competition and facilitation between plants act in combination with environmental factors to determine plant performance and population growth at this scale. Changes in climate or habitat variables are also likely to have direct effects of on many life-history traits in plants affecting physiology, phenology and fitness. Here historical distribution records from two time periods are used to provide a long-term perspective on distribution change. I consider the evidence for contrasting models of distribution change in the British flora and find that the spread and dispersal of most species is spatially restricted, likely as a result of habitat constraints. There is also evidence of climate effects on distribution change for many of the species studied. The roles of competition and facilitation along environmental gradients are assessed in winter annuals in sand dunes. Plant-bryophyte and plant-plant interactions are studied using removal experiments across multiple years. The results show that there may be spatio-temporal variation in the strength and direction of interactions in consecutive years. There also species and population-specific responses to experimental temperature increase in annuals, which take the form of plasticity and adaptation depending on the traits measured. Temporal variability may be equally, or more, crucial to the performance and growth of annuals than the role of spatial gradients in environmental quality.EThOS - Electronic Theses Online ServiceGBUnited Kingdo