The invertebrate biodiversity of differently aged arable farmland hedgerows under environmental stewardship

ii ABSTRACT Hedgerows have been a feature of the British countryside for many centuries and their value to wildlife particularly in farmed areas is long acknowledged. But farmland hedgerows experienced dramatic decline in the 20th century and efforts to halt this decline have been a focal point for agri-environmental activities, with hedge planting and management amongst the most popular options amongst farmers. Despite restoration of many thousands of kilometre of hedgerow under environmental stewardship, the rate of hedgerow loss exceeds the current rate of replacement. Information regarding the ‘performance’ of hedgerows as habitat for a range of wildlife is not lacking, although there is less current information regarding the biodiversity of the woody hedgerow itself as opposed to the grassy hedge bottom; I examine both elements of the hedgerow. There is less current information regarding invertebrates than for birds, plants or mammals. A lack of general monitoring has produced a deficit of knowledge of the role farmland hedgerows currently play in maintaining invertebrate biodiversity and what agri-environmental options have achieved. My objective was to compare and contrast the invertebrate faunas of hedgerows relatively newly-planted under agri-environmental schemes with existing hedgerow stock in order to investigate the biodiversity gains achieved by creation of new habitat. While it was true that overall the diversity of mature hedgerows was greater than that of new hedgerows, for some taxa newer hedges were ‘preferred’. There was evidence for the value of even relatively immature (~10 year-old) hedgerow habitats to overall invertebrate diversity. I did not use a single taxonomic group such as butterflies to ‘indicate’ diversity, but instead chose to take a view of the broad spectrum of invertebrates collected from both the hedge bottom and hedge top based on higher taxon approaches (notably order), which have been proposed as an adequate means of rapidly assessing the diversity of agricultural land. A suite of habitat variables including botanical diversity at hedge bottom and top, structural features including the height, width and density of vegetation, as well as weather data were recorded. While weather will always have the ultimate decisive influence on invertebrate activity, structural elements such as the sward height at hedge bottom and the density of the canopy are important to the invertebrate assemblage. As hedgerow conservation and management become increasingly important in the light of continuing declines, the ability to evidence the effects of interventions efficiently will be crucial. This research underscores the ongoing need for monitoring of hedgerow creation in order to verify whether biodiversity gains are achieved