AN EXPERIMENTAL FIELD-STUDY OF THE EFFECTS OF MOLLUSK GRAZING ON SEEDLING RECRUITMENT AND SURVIVAL IN GRASSLAND

1 The effect of mollusc herbivory on regeneration from seed was investigated for six common grassland species by sowing into artificially created gaps in a grassland award. Molluscs were excluded from half the plots by application of molluscicide. 2 Samples taken monthly from October 1993 until March 1994 showed that species composition was markedly influenced throughout the study by the application of molluscicide. Plots from which molluscs were excluded contained significantly larger seedling numbers of Agrostis capillaris, Senecio jacobaea, Stellaria graminea, Taraxacum officinale and Trifolium repens while Ranunculus acris populations were unaffected by grazing. 3 Analysis of percentage cover during the final three months of the study, showed that the vegetation in ungrazed plots contained a significantly greater proportion of Agrostis, Stellaria, Taraxacum and Trifolium. In contrast, mean percentage cover of Senecio jacobaea and Ranunculus acris was significantly higher in grazed plots, in which Senecio accounted for up to 80% of the vegetation. 4 Significantly more Agrostis, Stellaria and Taraxacum inflorescences were recorded in ungrazed plots suggesting that mollusc herbivory influenced not only seedling survival, but also the fecundity of mature plants, Senecio and Ranunculus inflorescences were more frequent in grazed plots,