Long‐term dynamics of the hemiparasiteRhinanthus angustifoliusand its relationship with vegetation structure

Questions:1. How are the long‐term dynamics of the root hemiparasiteRhinanthus angustifoliusrelated to vegetation structure, grassland management and climate? 2. DoesR. angustifoliushave a long‐term impact on standing crop and community composition? Location: A formerly fertilized grassland, part of a larger brook valley system in the nature reserve ‘Drentsche Aa’, near Groningen, The Netherlands. Methods: Vegetation development has been monitored since 1973 in 54 permanent plots in nine management regimes without fertilizer application. Results: 1. The hemiparasite established when standing crop was less than 600 g.m−2and performed best under annual haymaking using machinery. Since its appearance, the population fluctuated stochastically, with two peaks. Coinciding collapses in six adjacent grasslands and comparison with an integrated climatic index suggest that the population collapses are induced by spring drought. 2. We did not find a relationship between total standing crop andR. angustifoliuscover. Cover of grasses was negatively related to the abundance of the hemiparasite in the same and the previous year. Forb cover tended to increase with the parasite. Conclusions:R. angustifoliusshows stochastic population fluctuations, mainly determined by spring drought, to which this species is probably highly vulnerable because of its parasitic and annual life style without a persistent seed bank. The hemiparasite also shows long‐term relationships with grass cover (negative) and forb cover (positive), but it seems to have no lasting impact on standing crop.