The role of trees in maintaining biodiversity resilience and habitat connectivity in agricultural landscapes

Background.

Woodlands are increasingly recognised as key semi-natural habitats providing landscape complementarity to the seasonal availability of resources needed for farmland insect populations to complete their life cycles. This includes insects that are essential for provisioning of ecosystem services of benefit to farmers, such as pollination and pest control.

Less is known about the wider ecosystem benefits of tree species located in open farmland habitat, or along hedgerows outside woodlands. Common tree species (oak, ash and others) may enhance resilience of farmland biodiversity via their presence in linear habitat features (hedgerows), and/or by providing farmland biodiversity with increased shelter from climatic events e.g. heat waves.

Tree canopies have been relatively neglected in ecological studies, potentially under-estimating the food web linkages, and micro-climatic associations, between farmland biodiversity and trees in and outside woodland. Overall aims and methodology:

This project will investigate the role of trees outside woodland in the maintenance and resilience of insect communities in agricultural landscapes. Sampling of insects will be carried out in a selected study landscape in Norfolk comprising woodland patches connected by hedgerows with and without mature trees, as well as trees within fields.

Metabarcoding of bulk insect samples will increase the number of replicate samples (hundreds) that can feasibly be identified, as well as the taxonomic breadth of insects considered, and hence the statistical power of the data. Standard morphological taxonomy of selected insect groups (including pollinator taxa) will be used as a reference dataset against which to verify and complement the taxonomic resolution and composition of samples revealed by metabarcoding. Metabarcoding will be used to identify a wide range of insect orders present in trap samples.

The research design will focus on sampling flying insects at understory level along hedgerows, and in canopies of selected tree species present along hedgerows, in arable fields, and at woodland edges. Targeted repeat sampling in spring and summer will capture seasonal variations in insect assemblages. Data on timing of flowering of key hedgerow and hedgerow tree species will also be collected.

The project aims to address the following research questions:

(1) What is the contribution of mature trees to insect assemblages of hedgerows compared with those lacking trees, and what are the ecosystem service implications for farmland?

(2) How do insect communities in canopies of hedgerow trees compare with those of conspecific trees isolated within arable fields or embedded within woodland patches?

(3) How do insect communities associated with hedgerows and hedgerow trees vary seasonally and with temperature? An element of sampling of insects will focus on spanning seasonal and short-term temperature variations, including temperature spikes (heat waves). Use of data from temperature loggers positioned along hedgerows and woodland edges will allow the influence of temperature events to be studied.

(4) What are the optimal woody corridor management recommendations for maintaining resilient insect communities, hence ecosystem services, in agricultural landscapes? Drawing upon the study findings, here we will focus in on the role of trees in the landscape, and how to optimise environmental buffering and connectivity of biodiversity between woodland patches and cultivated landscapes.