Grazing impacts on moth diversity and abundance on a Scottish upland estate

Abstract

Abstract. Livestock grazing is the most important direct management impact on grasslands in upland areas of the UK. For phytophagous species, such as Lepidoptera, the impact is primarily through grazing altering the species composition and structure of the vegetation. However, specific impacts related to different grazing regimes are not well understood for this group of insects. Within a replicated controlled grazing experiment, nocturnal adult moths were sampled by light trapping in the fifth year after establishment. Sampling effort was standardised between the four grazing treatments by simultaneously using identical traps in each treatment. The highest‐intensity grazing treatment produced the lowest moth abundance and species richness. Ungrazed and low‐intensity sheep grazing treatments produced the highest moth abundance and species richness. Moths that feed exclusively on graminoids and moths that overwinter as larvae were disproportionately well represented in the ungrazed treatment. A sub‐set of species for which large declines have recently been documented in the UK were most abundant in the ungrazed treatment. However, they made up the largest proportion of the overall assemblage in the high‐intensity grazing treatment. Increased grazing inversely affects moth abundance and species richness. However, effects are not even across all moth species. An absence of grazing is likely to negatively affect the abundance of some moths, especially those that overwinter in the egg stage.