Studies in the Grazing of Heather Moorland In North-East Scotland. IV. Seed Dispersal and Plant Establishment in Dung

Abstract

Germination of seeds on dung deposited at moorland sites was recorded either in situ or in a glasshouse. Colonization by seedlings and peripheral vegetation was observed until plant cover became complete. Many more graminoid than dicotyledonous seedlings appeared on dung of cattle, red deer and sheep. On dung of grouse, hares and rabbits the ratio was roughly equal. Altogether 88 species were recorded as being transmitted by these herbivores, but only Agrostis tenuis, Calluna vulgaris, Cerastium holosteoides, Juncus spp., Poa pratensis, Rumex acetosella and Sagina procumbens gave numerous germinated seedlings. Many fewer seedlings were found on the dung left in situ than in the glasshouse. Dung deposited in spring also gave rise to fewer seedlings than autumn dung. Seedlings that arose by germination on dung gained much less cover than plants colonizing the deposits vegetatively. However, with cattle dung several transmitted species attained greater cover than in the previously existing vegetation e.g., C. holosteoides, Lolium perenne, Poa annua, P. pratensis, R. acetosella, Stellaria media and Veronica serpyllifolia. Surveys at the moorland sites showed that Anthoxanthum odoratum, Holcus lanatus, P. annua and P. pratensis were the grasses most frequently introduced; increase in the number of their establishments was associated with heavy dung deposition by cattle. Estimates were made of the contribution of dunging to the overall impact of the herbivores on the composition of the vegetation. Only with cattle were the effects appreciable, but the gains in cover of graminoids and herbs were less than the decline in C. vulgaris (heather) due to plant mortality below the deposits. About a quarter of the greater impact of cattle on heather compared to sheep could be ascribed to dunging.