Response of the alpine gentian Gentiana nivalis L. to protection from grazing by sheep

Protection from summer grazing by sheep was imposed experimentally from 198 7 to 1996 on colonies of alpine gentian Gentiana nivalis, a rare montane an nual growing in grassland at Ben Lawers National Nature Reserve. Alpine gen tians on ungrazed plots grew taller and survived better than did plants in adjacent grazed plots. The density of plants on ungrazed plots was unaffect ed for three years but thereafter declined. By 1996 it was only 20% of the density on grazed plots. Perennial vegetation responded to protection from sheep grazing by growing taller and denser. Ultimately it became 50-60 mm t aller in the ungrazed plots than it was in the grazed plots. The spread of perennials also progressively reduced the amount of bare soil in the ungraz ed plots-by 1996, it occupied a mere 0.2% there compared to 7% in the graze d plots. The loss of potential gaps for seedling establishment was probably the main cause of the decline in alpine gentian density on the ungrazed pl ots. The presence of sheep helps to maintain alpine gentian colonies in gra ssland. (C) 1998 Elsevier Science Ltd. All rights reserved.