A quantitative analysis of the environmental impact of hill farming in relation to vegetation, soil attributes and soil erosion: a land use perspective.

peer-reviewedThe research was carried out in conjunction with the commercially run Teagasc Hill Sheep Farm, Leenaun, Co. Mayo and with Met Éireann. The aim was to enhance habitat status and to maximise biodiversity conservation in the upland landscape of western Ireland through more evidence-based agricultural policies that are designed to maintain and improve agricultural productivity. Field data on vegetation frequency and composition over periods of 5 to 17 years, satellite tracking (GPS) of sheep and longterm trends in wind-driven rain were analysed. Vegetation frequency increased from a baseline of 64% in 1995 to 82% in 2008 at a mean annual stocking rate of 0.76 ewes/ha. Soil differences were responsible for most of the significant changes. Grazing reduced vegetation height by half, from 40 to 20 cm, thus opening the canopy and allowing an increase in species diversity in a number of instances. Long-term habitat exclosures revealed that grazing resulted in increased species diversity in acid grassland and lowland blanket bog and a significant increase in the frequency of sedges in all habitats. Winter grazing only, at 0.6 ewes/ha, which represents an annual stocking rate of 0.76 ewes/ha, was the most beneficial for total vegetation frequency and that of individual communities. Implementation of this management system would require substantial additional financial outlay. Restricted, temporary holding areas for animals resulted in substantial changes in vegetation composition but not in frequency. Average daily trekking by GPS tracked hill ewes varied from 2 to 3 km, which, at the present stocking rate, represented a mean daily trampling pressure of c. 2 km/ha. This pressure may be 5 to 10 times greater in areas preferred by sheep, which is why increasing trends, from 1950 to 2009, in aspects of wind-driven rain that are associated with peat erosion, are of serious concern. Regular monitoring of vegetation height by physiography and altitude is a key factor in appropriate grazing management. The development and introduction of wireless fencing together with sensors that attract rather than repel animals are necessary to achieve more even grazing pressure in a free-range grazing environment. Due to the likely synergy between increasing trends in certain aspects of wind-driven rain and peat erosion in areas of concentrated sheep activity, an early warning system similar to that for potato blight must be established