The Changing Abundance of Moths in a Tussock Grassland, 1962- 1989, and 50-Year to 70-Year Trends

Species-rich moth faunas at two sites in a montane tussock grassland at Cass show major declines in the abundance of many common species between 1961-63 and 1987-89, furthering a 50- to 70-year trend. The recent faunal record (202 species) is quantified by a 3-point light-trapping methodology based on independence of serial samples, minimised sample variability and a posteriori data standardisation. An historical record of vegetation change is also presented, pointing to a major decline in endemic herb species with the advances of an adventive grass, Agrostis capillaris. Site differences feature in the analysis of vegetation and faunal changes. At the site with the greater loss of herbs and the 93% grass cover (a doubling in 26 years), the respective abundances of common herb- and grass-feeding moth species have declined 88% and 74% since 1961-63. A greater residual floral diversity at the other site (13% herb cover, 71% grasses) has to date favoured a lesser decline in grass-feeders (56%). Data analyses suggest that few common endemic grassland moths can survive as oligophages, most depending on feeding diversity. In the face of reducing diversity, the thrust of faunal conservation in induced Agrostis associations should be to manage the vegetation using adventive animals as allies. The evidence of the study supports and extends the author's earlier conservation guidelines.