Individual study: Livestock trampling reduces the conservation value of beetle communities on high quality exposed riverine sediments along the Afon Tywi SSSI, Camarthenshire, Wales
Bates A.J., Sadler J.P. & Fowles A.P. (2007) Livestock trampling reduces the conservation value of beetle communities on high quality exposed riverine sediments. Biological Conservation, 16, 1491-1509
Exposed riverine sediments (ERS) are poorly vegetated, alluvial deposits of silts, sands and gravels which rely on flood disturbance for their maintenance in the face of successional pressures. In the UK, they provide habitat for a large number of rare and threatened specialist invertebrates, but are most notable for their rare beetle (Coleoptera) fauna. Some disturbance due to grazing by livestock is sometimes recommended as a management tool to maintain heterogeneity of some habitats, but livestock trampling is believed to be a widespread cause of damage to ERS habitats in the UK, and as such, its effects were the focus of the study summarised here.
Study area: The study was undertaken at sample sites from within the area delimited upstream by the confluence with the Gwydderig and downstream by the confluence with the Annell, all part of the Afon Tywi Special Site of Scientific Interest (SSSI) in South Wales.
Sampling: Sampling was undertaken from 13 July and 28 August 2003. Beetle density was measured within 25 distinct patches of habitat along the Afon Tywi special site which is known to support an extremely good quality ERS beetle fauna in a UK context. Environmental variables including categoristaion of trampling damage (from 1 - no damage; to 10 - very heavy cattle, structure completely destroyed + very heavily pitted), and faeces counts were used as additional (and quantitative) measure of the level of trampling, in the ERS habitat.
Analyses were undertaken to explore the relationship between beetle assemblage and a range of environmental variables.
During the study 2,456 individuals of 87 beetle taxa, 34 of which were ERS specialists, were recorded. Staphylinidae and Carabidae dominated the assemblages in terms of abundance of individuals and species richness.
The percentage of fine (<8 mm) sediments, median sediment size, distance downstream, cattle stocking levels, and counts of sheep faeces were found to best relate to beetle abundance and assemblage structure of the ERS. Beetle species richness increased with higher stocking levels, probably due to the presence of species associated with resultant elevated levels of silt and organic matter. Importantly however, the ERS quality score (a measure of conservation value based on the rarity of specialist ERS beetles), was negatively associated with measures of trampling damage.
The authors conclude that livestock trampling reduces the conservation value of beetle communities on high quality ERS along the Afon Tywi and management should be undertaken to restrict trampling in sites of high conservation importance.
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