Beneath the mistletoe: parasitized trees host a more diverse herbaceous vegetation and are more visited by rabbits

Abstract

Parasitism by mistletoe increases the cover and diversity of herbaceous vegetation under the host tree and attracts the activity of rabbits in comparison to control trees. Thus, the effects on forest community go beyond the parasitized tree. Mistletoes are a diverse group of aerial hemiparasitic plants and are considered keystone species in forest ecosystems around the world. They produce nutrient-enriched litter, which exerts a substantial effect on soil-nutrient concentration, and the enriched nutrient patch alters the vegetation at the site as well as the associated fauna. Our goal is to ascertain whether mistletoe (Viscum album) parasitism of pine forest of a Mediterranean mountain favors herbaceous vegetation and attracts mammalian herbivores. We recorded in Sierra de Baza (SE Spain) the composition of the herbaceous vegetation under pines with and without mistletoe parasitism, and estimated the rabbit activity at the same sites by collecting their excrements. An effect on herbaceous vegetation, especially in grasses belonging to the family Poaceae, was reflected in a notable increase in soil cover, species richness, and species diversity beneath parasitized pines with respect to unparasitized ones. As a consequence, parasitized pines attract the activity of rabbits, as shown by a fivefold quantity of excrement with respect to control ones. Parasitism by mistletoe, by creating patches of greater nutrient availability under the host canopy, extends its effects beyond the host tree to other members of the forest community, such as herbaceous plants and associated herbivorous animals, which in turn contribute to environmental heterogeneity with their activity.