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

Sarah H. Watts, Anna Griffith & Lindsay Mackinlay

The tall herb community thriving below a section of crags within the fence at Creag an Lochain, Ben Lawers NNR, Scotland. Photo credit: Sarah Watts.

In 2000, an electric deer fence was erected around 180 ha at Creag an Lochain in the Ben Lawers Natural Nature Reserve, Scotland. Owned and managed by the National Trust for Scotland, this upland site in the Southern Highlands is part of a Special Area of Conservation which is arguably the most important location in Britain for arctic-alpine flora. The fence was intended to exclude large herbivores (sheep and red deer) from the hillside and facilitate the restoration of threatened plant species and habitats which had been suppressed by overgrazing.  This included the tall herb community; a mix of tall, grazing-sensitive luxurious broad-leaved flowering plants which is found throughout upland Europe but currently has an unfavourable conservation status. 

Creag an Lochain contains a large, complex crag system with ledges inaccessible to sheep and deer on which trees, shrubs and tall herbs grow. In 2000, these contrasted with the grazed ground below where grasses were dominant, and the only tall plants present were either spiny or toxic. It was hoped that removing large herbivores from the site would promote the expansion of the tall herb community from patches on ledges into the calcareous grassland adjacent to the cliffs.

In this study, we investigate how the vegetation has changed within the Creag an Lochain fence after 18 years and whether the desired conservation outcome (an increase in tall herbs) has been achieved. In 1999, one year before the fence was built, nine transects were established running downhill from the base of the crags to the Lochan na Lairige reservoir below. The presence and abundance (estimated percentage cover) of all vascular plant species were recorded in sixty-three 2×2m study plots positioned at 30-m intervals along these lines. This was then repeated in 2017 using the exact same plot locations as 1999.

Some of the flowering plants featuring in the restored tall herb community at Creag an Lochain, Ben Lawers NNR, Scotland (Filipendula ulmaria, Valeriana officinalis, Cirsium heterophyllum, Cirsium palustre and Silene dioica). Photo credit: Sarah Watts.

The data analysis has shown that although the overall diversity of species remained unchanged between 1999 and 2017, the average number of tall herb species present in the plots increased significantly. There was a large expansion in the average tall herb cover (+29.7%) and a corresponding decrease in grass cover (-26.2%), as well as a smaller increase in moss cover and a reduction in bare ground. The composition of plants moved from a typical upland calcareous grassland towards a tall herb community. Amongst the individual species showing the greatest increase in cover were seven tall herbs (Luzula sylvatica, Alchemilla glabra, Filipendula ulmaria, Angelica sylvestris, Geum rivale, Rumex acetosa and Heracleum sphondylium), and the taller and shade-loving grasses (Holcus mollis, Deschampsia cespitosa and Deschampsia flexuosa). However, there were large declines in grazing-tolerant grass species and low-growing herbs which require gaps in the vegetation to survive. Understory species (for example Anemone nemorosa and Oxalis acetosella) capable of competing in the lower light levels created by the proliferating tall herbs had thrived.

We have therefore shown that large herbivore removal can be used to aid the conservation and restoration of the grazing-sensitive tall herb habitat at upland sites where it was previously confined to cliff ledges.

This is a plain language summary for the paper of Watts et al. published in Applied Vegetation Science.