How and where to restore habitat on farmland to increase the abundance and diversity of moths

Modern agriculture has severely impacted the variety of life on earth. Agricultural expansion has cleared >50% of natural habitats on agriculturally usable land, while agricultural intensification has reduced the abundance and diversity of wildlife in farmed areas. Agri-environment schemes (AESs) offer opportunities to restore habitats for wildlife in farmed landscapes across Europe and elsewhere. This could help to (1) reverse declines in species of conservation concern and (2) provide “ecosystem services”, such as pollination, which contribute to human wellbeing. AES interventions have led to increases in the abundance and diversity of wildlife. However, despite the scale of public investment in AESs, the size and significance of those increases are often unclear. Furthermore, the outcomes of AES interventions vary depending on features of the surrounding landscape, especially semi-natural habitat. Research to date has directed the allocation of AES interventions in a broad sense, for example towards landscapes with <20% coverage of semi-natural habitat. Still, there is a lack of specific advice about how and where to restore habitat on farmland to maximise benefits for priority insect species. I present two field studies of the abundance and species richness of night-flying Lepidoptera (moths) in the UK, aiming to develop advice for land managers implementing AESs. Focussing on moths in three distinct habitat specialism groups, I looked at how the benefits of two types of AES interventions were affected by the coverage of semi-natural calcareous grassland (CG) nearby. In the first field study I investigated the benefits of AES interventions that create wide grass margins on the edges of arable fields. I found that grass margins significantly increased the abundance of grassland generalist moths. Furthermore, grass margins benefitted CG-associated moths if there were large areas of CG habitat nearby. Therefore, spatial targeting of AES interventions towards semi-natural habitat has the potential to improve outcomes for biodiversity. In the second field study I investigated the benefits of AES interventions that restore arable fields to species-rich grassland. Restored grassland fields were similar to semi-natural CG in terms of moth abundance and species richness. Furthermore, CG moths were more abundant on restored grassland where CG indicator wildflowers were established. Grassland restoration is a particularly successful AES intervention, especially if the plant community is enhanced to support priority insect species. Finally, I present the first individual-based model to test how the benefits of AES interventions depend on distance from source populations on semi-natural habitat. By simulating larval and adult life-stages of hypothetical insect species, my model provided a set of mechanisms that help to explain my empirical field observations. Ultimately, this thesis presents two of the most robust field studies on the interaction between AES interventions and the landscape context. By interpreting these field studies in light of a supporting model, I produce clear advice for land managers interested in the conservation of moths and the other species with which they coexist.