Grazing exclusion and vegetation change in an upland grassland with patches of tall herbs

Questions The hydrophilous tall herb community is an important refuge for grazing-sensitive broad-leaved flowering plants. It is distributed throughout upland Europe but overgrazing has contributed to an unfavourable conservation status. To guide tall herb restoration, we asked: (a) Does using grazing exclusion where the tall herb habitat is confined to cliff ledge patches promote an expansion into the grassland below? (b) Does this management negatively affect vascular plant diversity? Location Ben Lawers NNR, Scotland. Methods Large herbivores have been excluded from a 180-ha area containing patches of outcrops rich in tall herb habitat. Using 1999 and 2017 surveys of permanent plot transects located in the grassland below (Before-After design), we quantify impacts on community composition and tall herb abundance. Results Species diversity remained constant although total species richness declined slightly and tall herb species richness increased significantly. There was a large expansion in tall herb cover (+29.67%) and a corresponding decrease in grass cover (-26.16%), as well as smaller increases in bryophytes and small herbs and a reduction in bare ground. Community composition shifted significantly from species typical of upland calcareous grassland towards those found in tall herb habitats. Seven tall herb species were amongst those showing the greatest increase in cover, along with taller grasses and understory herbs. Grazing tolerant grasses and low-growing, prostrate and annual herbs decreased. Competition for light, rather than resilience to herbivory, now has a major influence on the vegetation. Conclusions Using grazing exclusion where the tall herb habitat is largely confined to patches on cliff ledges facilitates an expansion into the upland grassland below. Although this management favours species tolerant of shadier conditions, there is no evidence of a negative impact on vascular plant community composition. It is therefore an effective strategy for promoting the restoration and favourable condition of this grazing-sensitive habitat.