Habitats and ecological niches of root-hemiparasitic plants: an assessment based on a large database of vegetation plots.

Root hemiparasites are a specialized group of green photosynthetic plants that obtain resources from the roots of other plants. Some root hemiparasites are considered to be important keystone species in temperate grasslands while others are listed as endangered. In this study, we used vegetation- plot data from the Czech National Phytosociological Database to construct habitat suitability models for root hemiparasites occurring in the Czech Republic. These models were based on a formalized vegetation classification, species co-occurrence patterns in vegetation units and actual presence of hemiparasitic species in the database. The resulting habitat models defined as sets of suitable plots for each species were further described by a climatic gradient, community Ellenberg indicator values and the leaf-height-seed (LHS) plant ecology strategy scheme values characterizing the associated vegetation. Using the properties of each vegetation unit, descriptors of the habitat suitability models and information from experimental studies, we interpreted the habitat suitability models as axes and shapes of ecological niches of individual root-hemiparasitic species. The individual hemiparasites differed in their favoured type of vegetation but almost all types of vegetation in the Czech Republic could host some of them. Semi-natural and natural grasslands with moderate availability of mineral macronutrients and water were identified as types of vegetation with a high incidence of hemiparasites and the highest number of species of hemiparasites. High incidence but low species richness of hemiparasites was recorded in forests and scrub. In contrast, most species of root hemiparasites did not occur in extreme habitats with a high level of stress or disturbance and at nutrient-rich and moist sites dominated by fast-growing species, i.e. at sites with intense above-ground competition. This reflects the ecophysiological fundamentals of the hemiparasitic strategy, which provides efficient yet low-cost access to below-ground abiotic resources. On the one hand, this advantage diminishes at sites where primary macronutrients and soil moisture are abundant but on the other hand, exploitation of this advantage, however, requires non-extreme environmental conditions. Apart from this common pattern, individual species of hemiparasites differ in their ecological requirements, which frequently underlie their possible use as ecosystem engineers in grassland restoration or their conservation status.