Quantifying the importance of tree floral resources for pollinators in urban landscapes

Urbanisation is accelerating globally, with the urban population projected to increase by 2.5 billion by 2050 (1). It is therefore expected that land-use change will increase correspondingly. Urbanisation is often linked to declines in biodiversity due to fragmentation and destruction of natural habitats (2). However, some pollinator populations may depend on urban areas as important habitats (3, 4).

Many studies have investigated the impacts of land-use change on pollinators, however there is a knowledge gap surrounding the importance of tree floral resources for pollinators. Despite trees being common in urban areas their resources are frequently overlooked. In studies which do consider urban trees, only low-hanging foliage accessible from the ground is sampled (5). As a consequence of this knowledge gap, it is challenging to create effective urban conservation strategies for pollinators.

Urban trees face many threats such as effects of the urban heat island, restricted rooting space, and water impervious surfaces (6). High maintenance costs have also led to the felling of many street trees. It is therefore essential to fill this knowledge gap and determine to what extent urban pollinators use tree floral resources and how important trees are for pollinators in comparison to other urban plants.

Research Questions: 1. How much pollen and nectar resources are produced by trees in urban landscapes? 2. How do pollinators use urban tree resources in urban landscapes?

3. What is the importance of urban trees for pollinators, and what is the importance of these pollinators for urban trees? 4. How does the addition of urban trees affect city-scale plant-pollinator community robustness? Research Methods: This research will span two field seasons in the UK.