Impact of management on biodiversity-biomass relations in Estonian flooded meadows

A negative species richness-productivity relationship is often described in grasslands at smaller scales. We aimed to study the effect of management on this relationship. In particular, we addressed the relative importance of biomass cutting, hay removal and nutrient impoverishment on species richness and growth form structure. We conducted fieldwork in flooded meadows in Alam-Pedja Nature Reserve, central Estonia. We sampled vegetation in managed and abandoned stands of two types of alluvial meadows, sedge and tall forb meadow. Aboveground biomass and litter were harvested, weighed and analysed for major plant nutrients by near infrared reflectance spectroscopy. Three groups of general additive models were developed and compared, addressing the impact of (i) productivity, (ii) nutrients and (iii) management regime on species richness. Management-mowing and hay removal-reduced the amount of litter but not aboveground biomass. Management led to a decrease in nitrogen in the biomass and enhanced species richness, particularly in the tall forb meadow. The strongest determinant of species richness was the amount of litter, exhibiting a hump-shaped relationship with richness. The effect of nitrogen supply was significant, but explained less variation. Management increased the proportion of sedges in the sedge meadow and of small herbs in the tall forb meadow. We conclude that litter removal is the most important management means to support biodiversity. On highly productive sites, reducing nutrients via hay removal is of secondary importance within a timeframe of 10 years.