In this post Michał Żmihorski discusses his paper ‘Effects of water level and grassland management on alpha and beta diversity of birds in restored wetlands’
A lot of species associated with wetlands are rare and declining and therefore large economical resources are being put into the conservation of wetlands given that they are hotspots for wetland birds and wet grassland birds. However, few studies have evaluated the effects of the wide array of factors that are influencing the abundance of wet grassland birds, including: effects of different management (grazing and hay-cutting), vegetation height, flooding dynamics (in comparison to permanently wet sites) and landscape openness (occurrence of woodlands) on biodiversity. These factors are usually difficult to separate or alternatively they are ignored. In our new paper we made an attempt to separate the effects of these different factors on birds, in order to give management recommendations for the conservation of wet grassland birds.
We collected data on bird communities over four years at 137 sites (each 3 ha) within five restored large wet grassland areas in Sweden. We conclude that local species richness (and occurrence of single species) at a site is mainly affected by water availability and landscape composition.
Flooded sites were preferred by most species, although permanently wet sites were preferred over drier sites. Management was not as important as flooding for local bird species richness, but total species richness at a larger landscape scale (including several sites in an area) was affected by management type, and total species-richness was clearly higher at grazed sites compared to sites used for hay-cutting. Grazing seemed to create a complex vegetation (patches with tall and short vegetation) suitable both for nesting (often in tussocks or tall vegetation) and foraging (open areas with short vegetation). Furthermore, the openness of the landscape was important for most wet grassland species, and many species avoided meadows close to forests.
Based on our results we draw three main recommendations for management:
- Priority should be given to regulate water levels to acquire beneficial conditions (moderate wetness and spring flooding) for wet grassland birds.
- Grazing by cattle should be promoted over hay-cutting on wet and flooded grasslands and this could be done through e.g. higher payments to grazed parcels in agri-environment schemes (AES).
- Reducing the amount of trees, shrubs or human constructions (such as electric lines), which are used as lookouts by avian predators, adjacent to wetlands could further enhance their attractiveness for wet grassland birds.