Agricultural landscapes impede woodland ground-dwelling beetle colonisation and establishment in planted woodlands

Abstract

Global insect declines have been partly attributed to habitat loss and agricultural intensification. Large-scale habitat restoration is crucial to address this biodiversity crisis, with woodlands representing a key habitat that supports diverse insect communities, particularly beetle assemblages. However, little is known about beetle colonisation and establishment processes as woodland is created. Using data from a long-term natural experiment (the WrEN project), we investigate the relative importance of local and landscape characteristics on ground-dwelling beetle colonisation and establishment across 60 UK secondary broadleaved woodlands. Our sites, planted 12 – 160 years ago, range in size between 0.5 – 32 ha and are embedded in landscapes ranging from 20 – 90 % agriculture. Using structural equation models, we show that woodland generalist and specialist beetles were more abundant in larger woodlands and more species-rich in woodlands with a lower proportion of surrounding agriculture. Woodland specialists were more abundant in woodlands with lower tree densities, a positive indirect effect of woodland age. Beetle community composition varied according to woodland age and structure, with younger and more homogenous woodlands having more non-woodland species. These findings suggest that the agricultural matrix may hinder woodland beetle colonisation into newly established woodlands in farmed landscapes. To enhance beetle biodiversity, woodland restoration initiatives should prioritise planting larger sites, and active management such as selective thinning that reduces tree density and increases structural heterogeneity. We highlight a potential paradox between the benefits of restoration that avoids landscapes with high agriculture to promote beetle colonisation vs. targeting these landscapes in efforts to enhance biodiversity.