Effects of late summer cattle grazing on the diversity of riparian pasture vegetation in an upland conifer forest

Abstract

1. Species-rich grassland is important for biodiversity in upland forests, particularly within riparian zones. Prior to afforestation, the botanical diversity of these grasslands was maintained by domestic stock grazing, but without active management many will revert to coarse, species-poor grassland and eventually to scrub. The reintroduction of stock grazing is a potential solution to this problem, but has not been tested in upland forests. Here we present results from 9 years of monitoring the effects of cattle grazing on the diversity and composition of riparian pasture vegetation in an upland conifer forest in northern Scotland. 2. There were two treatments, late summer grazing and ungrazed. The average stocking density in the grazed treatment was 2.25-2.5 cows ha-1. The cattle were free to range over the entirety of the 40-ha experimental site from early August to late September each year. 3. Assessments of plant species richness and abundance were made in 1988 (prior to the commencement of grazing), 1991 and 1997, in three of the main riparian vegetation types. These were 'Flush' vegetation associated with calcareous springs, acid Agrostis capillaris-Festuca ovina grassland ('Grass'), and Juncus effusus rush pasture ('Juncus'). Assessments were also made of grazing impacts, cattle usage and water table depths. 4. Grazing had a significant effect on plant species richness, which declined in ungrazed plots and remained static in grazed plots over the 1988-97 period. There were no recorded effects of grazing on species abundance, nor on the frequency of rare sedges and herbs of particular conservation importance. Litter cover (dead plant material) was significantly higher in ungrazed plots, which may be a causal factor in declining richness values. 5. Cattle utilized Grass and Flush vegetation to a significantly greater degree than Juncus vegetation, and this appeared to be related to forage availability rather than wetness as represented by water table depth. 6. Cattle grazing is of potential value as a management tool for species-rich grasslands in upland forests provided that: areas to be grazed are large enough to minimize localized impacts and allow free ranging of the cattle; the economics and practicalities of stock husbandry are considered; the type of grazing management used is linked clearly to management objectives.