Field margin botanical diversity, composition and quality on intensively managed farming systems

Abstract

Remaining semi-natural habitats are important refuges for farmland biodiversity, and field margins are one such habitat. Field margins consist of strips of herbaceous vegetation that are located between field boundary features such as hedgerows and the main grassland or arable field. However, little is known about their extent or ecological quality on intensively managed farmlands in Ireland. This lack of knowledge can only be addressed through the application of a standardised assessment methodology, which we developed and implemented in this study. A survey of field margins was conducted on 92 intensively managed farms, across three enterprise types (arable, beef and dairy farms) in Ireland. We describe the botanical composition and assess the ecological quality of field margins based on threshold levels of the percentage cover of positive, neutral and negative botanical indicator species that are predominantly informed by existing European Union (EU)-accepted methods for vegetation classification. Positive indicator species occurred in 77% of margins and had a mean cover of 10%. There was a high incidence of negative indicator species, occurring in 93% of margins with a mean cover of 55%. Using our quality appraisal system, 16% of field margins were of high or very high quality, and the majority (55%) were of low or very low quality. Compared to either arable or dairy farms, beef farms had a greater percentage of higher-quality margins, higher species richness and greater percentage of positive indicator species. Retaining areas of high-quality farmland habitat and enhancing those areas that have become ecologically degraded will be key to achieving the Common Agricultural Policy (CAP) objective of protecting landscapes and biodiversity. However, the implementation of appropriate management decisions requires effective evaluation of the current ecological condition of these habitats. Field margins are ubiquitous habitats in Irish farmlands and comprise a significant proportion of overall farmland habitat area. However, our results show that the majority in more intensively managed systems are in a botanically impoverished condition. Our standardised field margin quality assessment technique may offer an appropriate method of tracking change in habitat quality in response to conservation actions to improve habitat quality.