C. G. Maher

Atlantic floodplain meadows: influence of hydrological gradients and management on sciomyzid (Diptera) assemblages

AbstractMaintaining biodiversity is central to maintaining ecosystem functionality of wetlands. Hydrology has the strongest influence on wetland biodiversity, second to which agriculture is the most influential factor. This study investigates the influence of hydrology and farming practices on the abundance, species richness and composition of dipteran communities on temperate Atlantic floodplain hay meadows. Insects were sampled by sweep-net across twenty-four vegetation zones for which hydrological variables were calculated by combining river level data with fine-scale topographical data. Plant communities were surveyed using relevés and land owners were interviewed to gather data on current and past management regimes. A total of twenty-two sciomyzid species were recorded; over one-third of the Irish fauna. Flood depth and duration were found to have the strongest influence on sciomyzids, syrphids and plants. Sciomyzid species richness and total abundance were both positively correlated with hydroperiod and flood depth while both plants and syrphids responded negatively to increases. The difference in response highlights the need to assess more than one taxonomic group, when assessing the impact of changing environmental variables on biodiversity. Whereas vegetation structure drives changes in sciomyzid indicator species, plant species richness and composition, past management regimes and current nutrient inputs do not appear to influence these species. Thus, while the maintenance of the hydrological heterogeneity and the diversity of mowing regimes is important in maintaining biodiversity, variation in nutrient inputs and previous management (at least within the range here investigated) is likely to be of lesser importance for Syrphidae and Sciomyzidae.

Hydroperiod and Traditional Farming Practices Drive Plant Community Composition on Unregulated Atlantic Floodplain Meadows

The River Shannon, Ireland, among the last unregulated rivers in western Europe, has extensive floodplains and supports rare and endangered species and habitats, of ecological and cultural importance. Unregulated floodplains result in community composition responding directly to natural fluctuations in water level. This study assesses how hydrological factors and farming practices effect flood meadow plant communities. Three main plant communities were identified, forming an uninterrupted ecotone, along a gradient of dry to wet. Habitats of European conservation interest (Lowland Hay Meadows and Molinia Meadows) were well represented. Hydroperiod, calculated using microtopographical measurements, was the primary factor determining community composition and was negatively correlated with elevation and plant species richness. The botanical continuum comprised a range of insect-pollinated species, demonstrating the role of floodplains in providing pollinator services. Climate change projections indicate more prolonged winter flooding in the future, signifying potential range shifts for these plant species and communities; highlighting the need for appropriate conservation measures in the surrounding landscape. Low-intensity farming practices, with minimal fertiliser use and regular hay-mowing, played an essential, secondary role in maintaining plant species diversity. Retaining the floodplain topography, its associated hydrological regime and low-intensity farming practices, are necessary to maintain species diversity and ecosystem services.