The ecology of British upland peatlands: climate change, drainage, keystone insects and breeding birds

Northern peatlands provide important ecosystem services and support species adapted to cold, wet conditions. However, drainage and climate change could cause peatlands to become drier, threatening ecosystem functions and biodiversity. British blanket bogs occur towards the southern extent of northern peatlands and have been extensively drained, so present an excellent opportunity to examine climate change and drainage impacts.

Craneflies (Diptera: Tipulidae) are a major component of upland peatland invertebrate communities and provide a key food resource to breeding birds. However, larvae are highly susceptible to desiccation, so environmental changes that dry peat surfaces could harm cranefly populations and, in turn, bird populations. This thesis aims to examine effects of soil moisture, drainage and climate change on craneflies, and the relationship between craneflies and birds.

A large-scale field experiment showed that adult cranefly abundance increased with soil moisture. Areas with blocked drainage ditches showed significantly higher soil moisture and cranefly abundance than areas with active drainage.

A model of monthly peatland water tables driven by simple climate data was developed. The model accurately predicted water table position, and predicted up to two thirds of water table variation over time. Performance declined when modelling drained sites.

The water table model was combined with empirical relationships to model cranefly abundance under climate change. Falling summer water tables were projected to drive cranefly population declines. Drain blocking would increase abundance and slow declines, thus aiding population persistence.

Finally, modelled cranefly abundance was found to be a significant predictor of observed Golden Plover abundance, extinctions and colonisations on a large spatial scale. Across multiple species, variation explained by cranefly abundance was positively correlated with the proportion of craneflies in the diet.

Managing peatlands to maintain and increase cranefly abundance could be an important part of conserving upland bird populations.