Biodiversity change in the Irish uplands - the effects of grazing management

As a prominent form of land use across much of upland Europe, extensive livestock grazing may hold the key to the sustainable management of these landscapes. Recent agricultural policy reform, however, has resulted in a decline in upland sheep numbers, prompting concern for the biodiversity value of these areas. This study quantifies the effects of varying levels of grazing management on plant, ground beetle and breeding bird diversity and assemblage in the uplands and lowlands of hill sheep farms in County Kerry, Ireland. Farms represent a continuum of light to heavy grazing, measured using a series of field indicators across several habitats, such as the internationally important blanket bog, home to the ground beetle, Carabus clatratus. Linear mixed effects modelling and non-metric multidimensional scaling are employed to disentangle the most influential management and environmental factors. Grazing state may be determined by the presence of Molinia caerulea or Nardus stricta, and variables such as % traditional ewes, % vegetation litter and % scrub prove valuable indicators of diversity. Measures of ecosystem functioning, e.g. plant biomass (nutrient cycling) and % vegetation cover (erosion rates) are influenced by plant diversity, which is influenced by grazing management. Levels of the ecosystem service, soil organic carbon, vary with ground beetle abundance and diversity, potentially influencing carbon sequestration and thereby climate change. The majority of species from all three taxa are found in the lowlands, with the exception of birds such as meadow pipit and skylark. The scale of measurement should be determined by the size and mobility of the species in question. The challenge is to manage these high nature value landscapes using agri-environment schemes which enhance biodiversity by maintaining structural heterogeneity across a range of scales, altitudes and habitats whilst integrating the decisions of people living and working in these marginal areas.

The ecology of the Irish stoat

The Irish stoat, Mustela erminea hibernica (Thomas and Barrett-Hamilton), has been regarded as an intermediate between the British stoat and the weasel. In this study Irish stoats, mainly from road casualties, were collected and studied. A small number were also live-trapped and radio-tracked. Thus information was gathered on the stoat’s ecology, in particular its form (size and coat colours), reproduction, food habits, parasites, habitat utilisation mortality and predation. The Irish stoats studied were clearly not intermediate in size between British stoats and weasels. They showed considerable size overlap with British stoats, and marked size variation within Ireland. It is argued that size of stoats is determined by food supply early in life. The ventral coat pattern of Irish stoats is apparently unique in the Palaearctic, being similar to that of some stoats found on the west coast of North America. It is argued that this is an example of parallel evolution resulting from adaptation to similar climatic conditions. The stoats were reproductively active in spring and summer. Food consisted mainly of rabbits, but rats, birds, shrews mice and voles were also consumed. Mites were the most numerous ectoparasites, followed by lice, ticks and fleas. Damage by the parasitic nematode Skrjabingylus nasicola was found more frequently in female stoat skulls. Stoats were frequently found in a variety of habitats, both open and wooded. Some of the radio-tracked stoats climbed trees. Dens used were often rat holes. Only one home range, that of a breeding female, was considered to have been accurately measured. It was 22 ha. in size. Mortality is known to have been caused by road accidents and domestic carnivores. It is argued that predation by raptorial birds is important to stoat populations. Results of this study are compared with information available from elsewhere.