Factors affecting the diversity and abundance of roadside invertebrates and plants in urban areas

Abstract

With increasing human populations and a rise in people migrating to urban areas there will be a corresponding rise in urbanisation across the globe. Urban green spaces are therefore becoming increasingly important for biodiversity as reserves and movement corridors. This thesis aimed to understand the impacts of traffic and environmental related factors on the ability of green space to be wildlife reserves using the town of Bracknell, Berkshire, UK, as a model urban area. Concentrations of NO2 declined with distance from the road but urban green spaces showed many exceedances of NO2 and NOx critical levels. There were decreases in soil moisture and total C and N at the road edge but increases in soil pH, C:N, titanium, chromium, nickel, copper, zinc, cadmium and lead. Some protection of urban green spaces from the road could be achieved with the use of tree shelterbelts. It was found that roads had a significant affect on plant communities; with more bare ground, moss, herbs and stress-tolerator species and less grass and competitive species near to the road edge. These changes are related to differences in the environmental conditions at the roadside. Carabid species richness, abundance and diversity and invertebrate abundance and plant diversity were all higher at the road edge than the site centres, indicating that these groups are able to take advantage of the road edge habitat. Overall, sites with decreased mowing had more invertebrates and the bioindicators carabids and woodlice. Reducing mowing frequency therefore provides a simple method to improve urban green spaces for biodiversity. Furthermore, older and larger sites had greater biodiversity. This thesis has demonstrated that environmental and traffic related factors have significant effects on urban biodiversity. There are methods which could be employed, however, to lessen these impacts to allow urban green space to act as effective wildlife reserves.