The role of grassland sward islets in the distribution of arthropods in cattle pastures

1. It is well documented that cattle reduce their grazing activity in the vicinity of cattle dung, which gives rise to distinct patches, or islets as they have been termed, of longer sward. The influence of such islets on pasture utilisation and agronomic performance has been widely studied, but very little information is available concerning their influence on grassland biodiversity. 2. In this study the abundance and distribution of arthropods in relation to islets was assessed, using suction sampling, at 26 commercial farms and in a replicated pasture management experiment in the south and east of Ireland. 3. Islets were found to cover approximately 24% of pastures and to contain between 40% and 50% of arthropod individuals. 4. Islets consistently contained a higher density of arthropods, even when the difference in mean sward height between islets and more strongly grazed sward was accounted for. The relative concentration of arthropods in islets declined with increasing mean sward height, which may be related to the recovery of well-grazed non-islet sward. Islets appear to act as refugia from sward removal. 5. The potential importance of islets in maintaining arthropod biodiversity within intensively grazed pastures and the wider grass-based farming landscape is discussed, particularly with reference to standard agronomic practices such as sward topping and chain harrowing, which aim to remove the sward heterogeneity created by grazing livestock.