Hemiparasitic plants can influence the population dynamics and plant diversity of grasslands by (1) direct changes in vegetation structure [structural effects] and (2) indirectly by the redistribution of nutrients in the ecosystem [biogeochemical effects]. (1) Parasitic infection mostly causes total aboveground biomass to decrease. Furthermore, if dominant grasses are chosen as hosts, this may facilitate other species and increase species richness. (2) Parasitic plants act as a strong sink for water and nutrients from host plants, and therefore often produce fast-decomposing, high quality litter. This in turn may result in faster nutrient turnover and may possibly decrease species richness when higher nutrient availability favors competitive species. This research project aims to reveal whether structural or biogeochemical effects of hemiparasites dominate vegetation changes in grassland ecosystems with contrasting nutrient availability. The two main hypotheses are (1) the structural effects will dominate in more nutrient-rich grasslands, and (2) the biogeochemical effects will dominate in more nutrient-poor grasslands. The 2 species studied are Rhinanthus angustifolius, growing in rather mesophile grasslands and (2) Pedicularis sylvatica, growing in nutrient-poor heath grasslands. Experimental sites are all situated in nature reserves in Flanders.