Effect of Livestock Grazing on Water Beetle (Coleoptera) and Bug (Heteroptera) Assemblages in a Restored Salt Marsh: Different Responses to the Same Treatment (pp. 167-183)
Authors: (Ákos Molnár, János Oláh, József Szekeres, Pál Boda, Department of Systematic Zoology and Ecology, Lorand Eötvös University, Budapest, Hungary, and others)
Abstract: Pannonic salt marshes are among the most threatened European habitats with exceptionally rich wildlife and endemic species. Unfortunately, much of them were destroyed or damaged by long-term agricultural activities and land use in the past. A LIFE Nature and Biodiversity Programme was started to restore a former salt marsh in the Hortobágy National Park, Nagy-Vókonya Puszta area (East Hungary). This area was transformed to a goose-farm and rice field during the 1950-60s. Following the restoration of the hydrological regime in 2002, the area has been managing by livestock grazing.
We examined the response of water beetle and bug assemblages to this traditional land use method. Quantitative samples were taken both from grazed and intact (control) areas in the vegetation period of 2007 and 2008.
The examined aquatic taxa responded differently to the perturbation by livestock. Water beetles were affected in general negatively by grazing. Their abundance and diversity were lower in grazed areas, and 40% of the species showed strong preference to the control areas. The major effects of grazing that influenced water beetles were trampling of livestock, reduced vegetation and higher water temperature due to increased solar radiation in vegetation free waters.
Water bug assemblages showed the opposite patterns as they were more abundant and diverse in the grazed areas and 54% of the species preferred this treatment type. They responded positively to higher water temperature and to the increased sediment thickness due to trampling. There was a separation considering the functional feeding groups suggesting that grazing also influenced the food basis of the insects.
Although the primary objective of the salt marsh restoration and management by grazing was to provide suitable habitats for waterfowl and shorebirds, it also provided habitat for water bugs. However, grazing intensity at 0.9-1.3 animal unit/ha was not ideal for water beetles. Thus, we suggest the maintenance of both grazed and ungrazed areas in similar habitat restoration projects to maximize water beetle and bug diversity.