The role of woodlands in the diversity and resilience of pollinator communities in agricultural landscapes

Scientific background
Intensive agriculture is a key driver of declines in pollinating insect populations and pollination services. Ecological intensification to mitigate these effects has focused largely on restoring field-scale semi-natural habitat including flower strips and other habitat patches for grassland and wildflowers. The boost to floral resources provided by these agri-environment schemes typically span only a portion of the seasonal activity period for pollinating insect assemblages. Provision of pollination services on farmland is also dependent on wider landscape context, with relatively little attention being paid to the influence of woodland patches upon pollinator communities.
Uncertainty remains over which plant species are the most valuable food resources for pollinator species, and how their relative value varies seasonally. While the benefits to bees of grassland-associated wildflowers is well-established, the complementary role of trees and woodland in buffering the provision of pollinator resources (nectar and pollen) is less well-studied in agricultural landscapes. Woodlands can provide among the highest levels of nectar production for a major UK habitat, and the use by pollinating insects of tree species may be disproportionate to the abundance of woodland in the landscape. Woodland tree species composition also influences other plants, with consequences for pollinators. Woodlands and woody corridors (hedgerows) in landscapes provide nesting and larval microsites for a range of pollinator species.
Aims and objectives
This project will investigate the role of woodland in the maintenance and resilience of pollinator insect communities in agricultural landscapes. Sampling of insects will be carried out in a selected study landscape in Norfolk spanning a range of densities of woodland patches and hedgerow networks.
The project sets out to address the following key research questions:
(1) How similar are pollinator assemblages that occur in woodland canopies compared with those that occur at ground level, in woodland interiors and in more open farmland habitats? We will investigate which pollinator species show the greatest proportional occurrence in woodland canopies relative to more open habitats, and test for correlation between canopy occurrences and availability of either pollen and/or nectar sources in woodland canopies.
(2) Are pollinators found in or close to woodland canopies foraging on tree pollen resources? We will use molecular techniques to determine the identity of pollinator insect taxa, and their associated pollen, sampled from woodland canopies and at varying distance from woodland habitat. This work will establish which species of tree pollen, if any, are being used. We will test for circa 20 common woodland tree species, including some wind-pollinated species.
(3) Do woodland areas promote seasonal stability in pollinator diversity and abundance in the surrounding landscape?
The research design will focus on sampling within significant woodland patches within the study area, and at varying proximities to these patches within agricultural landscapes, including varying distances along hedgerows with and without trees. Repeat sampling in spring and summer will capture seasonal variations in pollinator assemblages.
(4) What are the optimal woodland and woody corridor management recommendations for maintaining resilient pollinator communities, hence pollination services, in agricultural landscapes? Here we will focus on the role of woody corridors as linear features in the landscape, and how to optimise their role in connectivity of pollinator assemblages between woodland patches and cultivated landscapes and maintain pollination services.