Greening cities: biodiversity and ecosystem services associated with street trees, from ecology to planning

This PhD project will investigate the role of an iconic but poorly studied system (street trees) for enhancing urban biodiversity and support ecosystem functions (e.g. pollination), and work with City Councils and other stakeholders to enhance policy and planning guidelines.

Background:
Across the world, cities are ever increasing in size, and there is growing interest in urban ecosystems, both in terms of fundamental research and applied practice. While there is substantial information on the ecology of urban green habitats (gardens, parks), little is known about ecosystems dominated by tarmac or concrete. It can be expected that in such environments, communities and ecosystem functions would be impoverished, but how much will depend on local conditions (e.g. area of exposed soil, type of cover, pollution), configuration of the cityscape, and the type of species. For instance, while ground insect diversity might reflect distance from sources (parks & gardens), flying pollinators might depend mostly on the availability of floral resources in the landscape, and their capacity to navigate that environment. To test these effects, street trees are an ideal system. They constitute highly replicated 'green islands' in a matrix of sealed surfaces (high consistency of planting patterns on individual street segments), but have been so far poorly studied. While they have been shown to have huge benefits for energy use and the wellbeing of urban users, their management is a controversial topic in the UK (see e.g. example link), and rarely includes wider ecological considerations. Across the world, cities are implementing tree planting strategies to increase carbon sequestration as well as address biodiversity objectives, making the study of urban trees urgent and impactful.

Study system: ground dwelling invertebrates and flying pollinators, in urban areas of Belfast, Aberdeen, and Malmo (Sweden). This may be expanded to other taxa and locations.

The project will address a number of ecological questions, selected within the first three months of the project in co-creation with the Belfast City Council. At this stage, they may include:
Can we detect Species-Area relationships at the base of street trees? What is the functional profile of species colonising street trees, and how is that determined by traits of the trees vs characteristics of surrounding cityscape? How does the diversity of species colonising street trees vary with the composition and configuration of the cityscape? How to increase the amount and diversity of floral resources available to urban pollinators? Can all pollinators fly through a city? Can we identify tree planting strategies that maximise biodiversity?