Vliv dračince rumělkového (Dracaena cinnabari) jako "nurse plant" na diverzitu cévnatých rostlin

Dracaena cinnabari, the dominant endemic tree of Socotra Island (Yemen), is in serious decline. The effect this will have on the island's plant diversity remains unknown. This dissertation aimed to assess the possible role of Dracaena as a nurse plant by identifying plants associated with Dracaena understorey and by assessing the importance of Dracaena for maintaining plant diversity. In the first part of the dissertation, relevés sampled in Dracaena understorey and in open sites to record the number of individuals of vascular plants were analysed. Species richness and composition were compared between understorey and open sites, and species associated with each of these habitats were identified. Additionally, the effects of shading and leaf litter on species richness and abundance were analysed. The second part of dissertation focused on mature woody species composition of Dracaena stands and investigated spatial relations between Dracaenas and other mature woody plants. The last part of the dissertation aimed to assess the fine scale spatial relationships between stones and plants in Dracaena stands and evaluated the differences of these relationships between understorey and open sites. The results confirmed the Dracaena role as an important nurse plant. The tree enhances the environmental heterogeneity and its presence creates two distinct microhabitats (understorey and open sites). The understorey habitat, compared with open site, harbours higher number of species, including endemics. The species in Dracaena stands can be classified as either understorey specialists, open-site specialists or generalists. The decline of Dracaena will negatively affect plant diversity, will reduce abundance of rare endemic plants and will lead to homogenization of vegetation. As no other tree species exists which could replace the Dracaena, our findings underline the importance of conservation efforts to preserve Dracaena stands on Socotra and identify this species as a key umbrella species whose conservation would ensure also the protection of a number of other associated species