Habitat management varying in space and time: the effects of grazing and fire management on marshland birds

Abstract

Freshwater wetlands and marshes with extensive reed beds are important hotspots of biological diversity, but in the absence of proper management, they are subject to biotic homogenisation. We assessed the impact of spatiotemporally variable management by cattle grazing (for 4 years) and late-summer burning (1 or 3 years before the study) on both songbirds and non-passerines in a previously homogeneous reed bed. We surveyed birds using a combination of line transects and point counts in a quasi-experimental design comprising six treatment levels. Management increased both the diversity of marsh habitats and the diversity of bird species. The species richness and abundance of non-passerines (ducks and geese, wading birds, gulls and terns, rails, coots and grebes) was higher in recently burned than in unburned or old-burned patches. Species richness of farmland songbirds was higher in grazed than in non-grazed patches, and the richness and abundance of reed songbirds was higher in unburned, old-burned, and grazed patches than in recently burned patches. Total Shannon diversity and evenness of birds was lowest in areas with the most intensive treatment (patches grazed and twice-burned), whereas Simpson diversity was highest in these areas. Non-managed patches had fewer species and individuals of all groups except reed songbirds. The proportion of old reed was low in recently burned and grazed patches, and was similarly high in all other treatment areas. No other property of reed stands was influenced by management, and both the allocation and the effect of management were independent of water level. Spatiotemporally variable management by cattle grazing and late-summer burning may thus simultaneously benefit several groups of birds. The effect of burning alone disappeared in 3 years, even in the presence of grazing; thus it must be repeated every 2–3 years. We conclude that both management actions are necessary to establish and maintain highly diverse habitats for marshland bird communities.