Local and regional factors affecting the distribution of the endangered holoparasite Cuscuta epithymum in heathlands

During the past few decades, many heathland species in Western Europe have declined significantly, mainly because of habitat loss. In particular, species that need active management for their survival may be more prone to extinction than later successional species. In this paper, we tested if six local factors (type of last management, canopy height, % cover of bare soil, pH and mean Ellenberg N (productivity) and F (soil moisture)) and/or three regional variables (patch size, patch age, i.e. interval since last practice, and isolation) have impact on the distribution and abundance of the endangered holoparasite Cuscuta epithymum. The presence of this species, its population size and host range were studied in more than 160 heathland patches within four nature reserves in Flanders (Belgium). The structure of the canopy, determined by management, was the key factor controlling the abundance of this species. The parasite performed best (in terms of population size) in patches which has been managed (mowing, burning or turf-cutting) in the previous seven years, mainly composed of young Calluna vulgaris individuals and had a canopy height between 10 and 30 cm. However, contrary to expectations, distribution patterns were not related to any other local or regional variable, except for site location. We, therefore, suggest that the current distribution of C. epithymum in this dynamic heath landscape may be driven by the presence of a persistent seed bank.