The abundance and reproductive success of the orchid Calypso bulbosa L. in relation to forest structure

Abstract

This seven-year study investigated the effects of forest structure and fragmentation on the Calypso orchid (Calypso bulbosa) (Orchidaceae). The species was found to prefer growing sites in the interior of the forest and near small openings. Proximity to clear-cuts and to openings had no effect on reproductive success. High canopy cover and shrub cover reduced the number of plants, while high shrub cover reduced the number of flowering plants. This in turn may affect the behaviour of bumblebees (Bombus spp.), the main pollinators of the Calypso orchid, and their ability to find and pollinate a plant. The number of flowering and pollinated plants was higher in large populations than in small ones. The long-term reproductive success of large populations, as measured by flower and fruit production, was more stable than that of small populations. Despite its status as a strictly protected species, the Calypso orchid is threatened by forest management, particularly in privately owned forests. Nature-friendly harvesting methods, such as selection harvesting and small-gap harvesting without soil preparation, may prove to be appropriate forest management practices in the species’ sites.